Silane surface modification is an important tool applied to improve and/or change the properties of various substrates which find applications in various industries including medicine, transportation, construction, energy, biotechnology etc. Maintaining the integrity of the treated surface is very important to ensure the longevity and performance of the coating; however this is affected strongly by the wetting interactions at the interface.
Dipodal silanes possess two silicon atoms that can covalently bond to a surface (whereas conventional silane coupling agents only offer one such silicon atom for surface attachment). Dipodal silanes offer a distinctive advantage over conventional silanes in terms of maintaining the integrity of surface coatings, adhesive primers and composites in aqueous environments through improved ‘wet&’ durability. Such improved durability is associated with an increased crosslink density of the interphase formed across the surface, and its resistance to hydrolysis. Calculations based on the equilibrium constant for dissociation of the Si-O-Si bonds to silanols suggest that dipodal silanes may have 100,000 times greater resistance to hydrolysis than conventional silanes. Hydrolytic stability data for dipodal silanes with both hydrophobic alkyl functionality and hydrophilic PEG functionality will be compared to that obtained for conventional silanes, titanates and phosphonates with similar functionality. New dipodal silanes with “pendant” rather than “bridged” functionality will be introduced together with their stability data in aqueous environments. Significantly, in neutral and mildly acidic environments, dipodal silanes clearly demonstrate improved resistance to hydrolysis compared to conventional silanes, titanates and phosphonates, with several hydrophobic “pendant” dipodal silanes providing the best performance.

Electrochemical oxidation lithography is a scanning force lithography mode which demonstrated to be a useful tool to fabricate nanostructures with nanometer resolution. Applications of this technique include the fabrication of split-ring resonator arrays for plasmonic applications, as well as the fabrication of nanoelectronic device features, i.e., nanometric gap structures,[1] carbon nanotube assemblies,[2] single particle placement among others. The functionalization steps involved in the fabrication of such structures strongly depend on the wetting properties of the templates as well as on the utilization of tailor-made chemical interactions. In particular for optical applications there is a strong desire to utilize substrates others than silicon wafers for the fabrication of nanostructures. Up to now these possibilities were not at hand. Here we report on the extension of the range of suitable substrates for the electrochemical oxidation and functionalization process. Electrochemical oxidation lithography is based on the local electrochemical oxidation of a self-assembled monolayer consisting of n-octadecyltrichlorosilane (OTS) by means of a negatively biased conductive SFM tip. The self-assembly of OTS is however not limited only to the functionalization of silicon but can be applied also to a number of other technologically relevant materials, i.e., indium tin oxide, titanium dioxide and metal oxides like aluminum oxide. We investigated the peculiarities of the self-assembly of OTS on these substrates and studied in detail the characteristics of the electro-oxidation process. Essential parameters for the self-assembly as well as for the oxidation process are presented in a comparative study. In depth Scanning Kelvin Probe investigations were performed with the aim to elucidate the chemical nature of the formed species in the oxidation process. As a main result the strong shielding performance of the OTS monolayer could be demonstrated which effectively screens the surface potential of the underlying substrates; a result which has significant impact in the design and manipulation of electronic properties of nanostructured surfaces.[3]
These results open on the one hand the spectrum of applicable substrates for the fabrication of functional nanostructures and pave on the other hand also the way towards new applications since for the first time also transparent substrates could be used to combine the advantages of electro-oxidative SFM lithography with applications which essentially require transparent substrate materials.
[1] T.S. Druzhinina, S. Hoeppener, U.S. Schubert, Small 2012, 8, 852-857.
[2] T.S. Druzinina, C. Höppener, S. Hoeppener, U.S. Schubert, Langmuir 2013, doi.org/10.1021/la4000878.
[3] D. Meroni, S. Ardizzone, U.S. Schubert, S. Hoeppener, Adv. Funct. Mater. 2012, 20, 4376-4382.

The iCVD method is a powerful technology for engineering surfaces which utilizes the richness organic chemistry. In many cases, covalent bonding (grafting), can be achieved at the interface between the substrate and the film. The resultant conformal polymeric coatings, deposited without solvents, and at low substrate temperature (~room temperature), represent an enabling technology in many different fields of application.
For iCVD, one or more monomers species are feed simultaneously with an initiator into a vacuum chamber (~0.1 to 1 torr). The initiator, typically tert-butyl peroxide, thermally cracks over resistively heated filament wires (~250 to 300°C). The radicals produced initiated chain growth polymerization of the monomers on cooled surface (~25°C).
Surface Energy Control:
For poly(perfluorodecyl acrylate), p(PFDA), the degree of crystallinity and the orientation of the crystallites, parallel or perpendicular to the substrate, and the surface morphology, can be tuned using the iCVD process parameters (initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Grafting is achieved by covalently bond of trichlorovinylsilane vapor to a silicon wafer. Polymerization through the surface vinyl groups creates anchoring point for synthesizing grafted polymer chains, resulting in durable superhydrophobic and oleophobic surfaces.
Surface Texturing Control:
Trichlorovinylsilane has been used as an adhesion promoter between polydimethyldisiloxane (PDMS) and heavily crosslinked, hard, poly(ethylene glycol diacrylate) p(EGDA) films deposited by iCVD. This system is buckled to construct highly ordered herringbone patterns through a new sequential wrinkling strategy.
Prevention of Biofouling on Reverse Osmosis Membranes:
The amine groups present in RO membranes with maleic anhydride (MA) at the interface between a zwitterionic polymer and substrate to form covalent bonds. Without MA grafting, zwitterionic films delaminated from the membrane when placed in water. The ultrathin (~20 nm) iCVD films showed anti-fouling properties against proteins and microbes without significantly impairing water flux or salt rejection performance.
Responsive iCVD films for biotechnology:
Longitudinal tissue constructs were formed inside the microgrooves of PDMS conformally coated with iCVD poly(N-isopropylacrylamide), p(NIPAAm). Its temperature response produces both swelling and a hydrophilicity change, allowing retrieval of the tissue construct from the microgroove, useful for 3D cell culture applications in tissue engineering and drug discovery

In nature, an electrical potential generated by an ionic gradient across the cell membrane plays a vital role in regulating the behaviors of membrane proteins for functioning. Examples of such proteins include certain G-protein-coupled receptors that undergo a conformational change upon electrical perturbation in the cell membrane and alter their binding affinities towards agonist ligands. Inspired by this notion, we designed a smart surface featuring a voltage-sensing molecular monolayer of an ionic headgroup-appended oligoether. By a conformational change in response to an applied electric field, this monolayer can capture and release a dendritic ionic guest molecule. When the conformational transition is restricted by a congested molecular design, the monolayer is not operable electrically in guest release. This finding not only paves the way for new electroactive materials affording high responsiveness and broad control scopes, but also provides implications for understanding the essential role of membrane potential in the function of membrane proteins.

Superhydrophobic surfaces, such as lotus leaves [1], exhibit extraordinary water repellent and self-cleaning properties. Recently, superhydrophobic surfaces were combined with photocatalytic materials to produce multifunctional surfaces. Reports on the preparation of superhydrophobic photocatalytic surfaces are limited and the techniques are problematic. Either they were created under extreme experimental conditions or the catalyst particles were embedded in the polymer matrix with reduced surface contact area, leading to lower photocatalytic activity. Scaling these techniques to produce large areas would be difficult. In addition, some films were not robust and lost their superhydrophobicity upon light irradiation.

Here we present a novel method for preparing superhydrophobic surfaces composed of photocatalytic particles. No chemical modification of the particle surfaces was required to achieve superhydrophobicity. Superhydrophobic surfaces were fabricated by printing polydimethylsiloxane (PDMS) into arrays of cylindrical cones that measure 400 µm base diameter, 25 µm tip diameter and 1000 µm tall on 500 µm pitch[2]. Catalyst particles of silicon phthalocyanine dispersed in a glass matrix, which we have shown to generate singlet oxygen (1O2) under 669nm light irradiation[3], were adhered onto the printed PDMS posts. Superhydrophobicity can be maintained, even with hydrophilic catalytic particles, due to this significant hierarchical structure. The surface has a water contact angle of 160° and maintains superhydrophobicity in contact with water under visible irradiation from a diode laser.
Another important feature of the high aspect ratio primary roughness is that it enables easy access to the plastron, i.e. the stable layer of air under the solid-liquid interface. Printing the PDMS posts on a porous membrane, and supporting the membrane over a plenum, provides a means to control the gas composition of the plastron and thus study catalysis at the solid-liquid-gas interface. The generation of 1O2 in the plastron region and the trapping of this short-lived reactive species after it travels across gas-liquid interface and is solvated in the supported solution were demonstrated. Because 1O2 generates no waste or byproducts, the fabricated superhydrophobic and photocatalytic composite surface can be used in water purification and disinfection, such as oxidizing toxic organic molecules and deactivating bacteria[4], as well as the synthesis important intermediates. Quantification of 1O2 as a function of plastron gas composition and flow rate was achieved using 9, 10-anthracene dipropionic acid as the trapping agent.
References
1. W. Barthlott, C. Neinhuis. Planta 1997, 202, 1-8.
2. M. Barahman, A. M. Lyons, Langmuir, 2011, 27, pp 9902-9909.
3. D. Bartusik, D. Aebisher, B. Ghafari, A. M. Lyons, A. Greer, Langmuir 2012, 28, 3053.
4. D. Bartusik, D. Aebisher, A. M. Lyons, A. Greer, Environ. Sci. Technol. 2012, 46, 12098.

Hydrophilicity is desirable for membranes in the water sector. Hydrophilic surfaces are less susceptible to fouling. They also improve water flux by facilitating more complete wetting of membrane structures to increase their effective porosity. However, most membranes are made from relatively hydrophobic polymers selected for their superior stability, mechanical integrity, and compatibility with traditional phase inversion fabrication techniques. Methods to hydrophilize hydrophobic membrane surfaces (e.g., plasma treatment, polymer chain grafting, or nanoparticle attachment) often suffer from lack of effectiveness, stability, or scalability. Additionally, they may compromise membrane performance by obstructing membrane pores or damaging structures that provide membrane selectivity.
In light of these challenges, a facile method for fabricating hydrophilic electrospun mats was developed. Stable nanofibers were electrospun from a solution of polysulfone (PSf) and polysulfone-block-poly(ethylene glycol) (PSf-b-PEG) in N,N-dimethylformamide. The ratio of PSf-b-PEG to PSf homopolymer in the electrospinning solution was varied, along with the total polymer concentration, to obtain nanofiber mats of differing composition and comparable structure. The nanofiber mats were then annealed in warm deionized water to drive the hydrophilic poly(ethylene glycol) (PEG) blocks toward the nanofiber surfaces. The water-insoluble PSf block and PSf homopolymer anchor the hydrophilic PEG block to the rest of the fiber, preventing its dissolution into aqueous environments.
As-spun and annealed fibers and fiber mats were characterized for morphological and material properties. Scanning electron microscopy shows that the fibers are cylindrical and mostly smooth with mean fiber diameters of 200 to 300 nm. Water contact angle decreased as annealing time increased, with drops from over 140° to less than 10° occurring with high PSf-b-PEG content and long annealing times. X-ray photoelectron spectroscopy revealed an increase of C-O bonds relative to C-C bonds as contact angle decreased, indicating that the reduction in contact angle was due to enrichment of PEG blocks at the fiber surface. Transmission electron micrographs and elemental mapping of the low contact angle fibers show that the fiber surface retains some PSf; the PEG enrichment that occurs does not form an exclusive PEG layer. Organic carbon concentration in the water used to anneal the fibers was low but increased with annealing time. When tested as a microfiltration membrane under gravity-driven flow, nanofiber mats rejected latex particles while allowing high water flux.
The use of PSf and PSf-b-PEG in this work demonstrates the potential this fabrication method has as a platform for producing high performance membranes. The bulk and surface properties of nanofibers can be tailored through custom pairing of other homopolymers and block copolymers to achieve application-specific membrane design requirements.

Osmosis describes the flow of water across semipermeable membranes powered by the chemical free energy contained in salinity gradients. It is a fundamental transport process for water in all living systems, and its applications are countless. While osmosis can fundamentally be expressed in simple terms via the van&’t Hoff ideal gas formula for the osmotic pressure, it is a complex phenomenon taking its roots in the subtle interactions occurring at the scale of the membrane nanopores.
I will first discuss some molecular views of osmosis, allowing to rationalize the osmotic pressure across nanochannels. I will then show that specific designs of nanofluidic devices allow to build an osmotic diode, leading to water flow rectification. This osmotic diode functionality opens new opportunities for water purification and complex flow control in nanochannels.
I will then report experiments on fluid transport at the nanoscales, in particular across nanopores, nanochannels and nanotubes. I will first demonstrate osmotically driven flow in nanochannels, as well as flow rectification in asymmetric nanochannels in line with the theoretical predictions for the osmotic diode.
Finally I will focus on the study of osmotic transport inside a single Boron-Nitribe nanotube. This trans-membrane nanofluidic device was developped using nanomanipulation tools using nanoscale building blocks. Experiments show unprecedented energy conversion from salt concentration gradients. Applications in the field of osmotic energy harvesting will be discussed.
References: see http://www-lpmcn.univ-lyon1.fr/~lbocquet
laquo; Giant osmotic energy conversion measured in a single transmembrane boron-nitride nanotube raquo;, A. Siria, P. Poncharal, A.-L. Biance, R. Fulcrand, X. Blase, S. Purcell, and L. Bocquet, Nature 494 455-458 (2013)
laquo; Nanofluidic osmotic diodes raquo;, C. Picallo, S. Gravelle, L. Joly, E. Charlaix and L. Bocquet, submitted (2013)
laquo; Soft nanofluidic transport in a soap film raquo;, O. Bonhomme, O. Liot, A.-L. Biance, and L. Bocquet, Phys. Rev. Lett. 110 054102 (2013)
laquo; Nanofluidics, from bulk to interfacesraquo;, L. Bocquet , E. Charlaix, Chemical Society Reviews 39, 1073 - 1095 (2010)

Materials with superhydrophobic properties are usually generated by covering the surfaces with hydrophobic nanoscale rough features. A major problem, however, for any practical application of such strongly water-repellent surfaces is the mechanical fragility of the nanostructures. Even moderate forces caused by touching or rubbing the surfaces are frequently enough to destroy the nanostructures and lead to the loss of the superhydrophobic properties. In this paper we study the mechanical stability of superhydrophobic surfaces with three different topographies i.e. with nano- and microscale features and surfaces carrying a combination of both. The surfaces are generated by silicon etching and subsequent coating with a monolayer of fluoropolymer (PFA). We perform controlled wear tests on the different surfaces and discuss the impact of wear on the wetting properties of the different surfaces.
A second system exhibits two roughness levels: silicon microcones surrounded by superhydrophobic silicon nanograss. The fabrication process of the surface structure is a mask-free process where both microcones and nanograss are simultaneously fabricated by the Deep Reactive Ion Etching (DRIE) technique in the overpassivation regime. Varying the process parameters, microcones of different size and density were fabricated, while the nanograss size and distribution was kept constant.
When strong shear stress is applied to such substrates, the microcones take the load and prevent contact of the shearing surface with mechanically instable silicon nanostructures. As result, the surfaces can withstand strong shear forces without noticeable loss in superhydrophobicity. Even when the shear stress is so very large that large scale mechanical damage happens the surface remains superhydrophobic (albeit with slight pinning caused by released hydrophilic areas from broken microstructures. Higher densities of microstructures make the surfaces much stronger against high shear forces, while causing slightly stronger pinning. Thus designing the surface structure allows to precisely tailor the mechanical and wetting properties of such nanostructures surfaces.

The wettability of surfaces is an important aspect of modern materials engineering. The ability to control the wetting behavior is a key feature in fields like surface coating, adhesives and microfluidic applications. We present a new method using femtosecond-laser micromachining to produce controlled wettability in a one-step process on metallic surfaces. Previously separated processing steps have been merged into a single-step, which results in better precision and a drastic reduction of process time. Thereby, we benefit from the femtosecond laser&’s property to alter both the surface topology and the chemical reactivity of a solid surface. Our method bases on the phenomenon that surfaces, which are chemically activated by femtosecond-laser micromachining, react with oxygen containing gases or gas mixtures to satisfy the oxygen deficit that originates from the exposure to femtosecond-laser irradiation. Modifying the surface chemistry consequently increases or decreases the original contact angle of the metal.
We have conducted the micromachining process on titanium (99.9%) under controlled conditions in different background media like oxygen, carbon dioxide and water, which serve not only as chemical reactant for the activated metallic surface but also contribute to the formation of the microstructure. Thereby, the background media influence the effective laser energy exposure of the target surface. Environmental parameters like temperature and pressure have been varied to study their influence on the outcome of the experiments. We have been able to render surfaces either hydrophilic or hydrophobic to different extents. Furthermore, we have controlled the formation of the nano- and microstructure via the parameters of the laser micromachining process, which has allowed us to reach superhydrophobic and superhydrophilic wetting behavior.
With this method we open a new field of possibilities to customise the wetting behavior of metals for various engineering applications to reduce consumption of energy and raw materials.

Electrospinning is a simple and useful method for producing various fiber assemblies by controlling the polymer solution and electrospinning parameters. The fibers can be spun into nonwoven structures having high porosity, small pore size and high surface-to-volume ratio. These electrospun membranes more hydrophobic than the corresponding cast films due to the air trapped in the voids of the membranes. High porosity combined with high hydrophobicity is desirable for membrane distillation desalination, in which water is transported through the membrane preferentially as vapor, due to a modest temperature differential across the membrane. In this work, various polymer fiber membranes are fabricated by the electrospinning technique. The membrane structure, porosity, hydrophobicity, and the effect of post-spin treatment, such as thermal annealing and modification of surface chemistry by initiated chemical vapor deposition, are studied. The electrospun fiber membranes are tested for desalination using the air gap membrane distillation configuration. The effect of membrane properties and the operating conditions on the membrane distillation performance are discussed.

The contact angle for a surface-liquid combination is governed by energy minimized states, also known as wetting states. One indicator of a wetting state is the penetration depth of the liquid inside the valleys of a rough surface. A clear quantification of the wetting thermodynamics, and explicit formulations for the contact angle have been limited to wetting states with complete penetration (Wenzel) and no penetration (Cassie). Over the past decade, several theories have been established which hint at an intermediate wetting state characterized by a partial penetration of the liquid inside the roughness valleys. This work aims at understanding the occurrence and thermodynamics of an intermediate wetting state. Assuming forced wetting arising at the apex of the roughness valley, the occurrence of a wetting state is realized by balancing the pressures acting on and away from the given surface with a square pillar topology. It is found that impact below a threshold velocity leads to the formation of an intermediate state. The feasibility of one wetting state over the other is governed by the surface characteristics. The principle of energy minimization is used to introduce the general equation of wettability, which computes the contact angle for any wetting state. A wetting parameter is incorporated, which forms the fingerprint of a wetting state. The wetting parameters corresponding to zero and complete penetration respectively return the Cassie and Wenzel equations. The intermediate wetting state is expressed by an implicit solution that is in good agreement with energy minimization. The physics of an intermediate wetting state is revisited, and a mathematical tool is provided which promises significant convenience in contact angle calculations.

With 15% CuInGaSe2(CIGS) and 11% efficiency Cu2ZnSn(S,Se)4(CZTS) solar cells reported, hydrazine-based spin coating technique has proven to be an effective method for fabricating Cu chalcogenide thin films and devices. During the solution-based process, drops of hydrazine solution interact with the substrate and, ideally, wet, spread, and form a coherent film as the solvent evaporates. One of the crucial factors that affect the film quality and device performance is the wettability of the hydrazine-CZTS solution on the substrate. Here we report a study on the wetting and spreading of hydrazine-CZTS slurries on various solid surfaces. Using surface tension calculations as our guide, we were able to alter the wetting behavior by controlling the solution composition and varying the hydrophobicity of the substrate surface through thin film addition. As predicted by our model, we were able to achieve improved wettability and, subsequently, smoother films.
To characterize the wettability and adhesion of hydrazine-CZTS slurries on various substrates, the surface tension was measured using a static contact angle method. 8 µL hydrazine-CZTS slurry was placed on various surfaces including soda-lime glass, Si, transparent conducting oxides (ITO, SnO2, ZnO), wide band gap chalcogenides (CdS, In2S3, ZnS), metals (Mo, Cu, Au, Al), carbon single-walled nanotubes (SWNTs), and CZTS thin films.The contact angle was measured macroscopically by using image analysis of a droplet on the substrate surface. The work of adhesion between the solid-liquid interface and the spreading coefficient for the droplets were determined using Young&’s equation. The work of adhesion and spreading coefficient for Mo and the CZTS slurry interface were measured to be 133.2 mJ/m2 and -0.37 mJ/m2, respectively. In comparison, those values for soda-lime glass and the CZTS slurry interface were 124.5 mJ/m2 and -9.24 mJ/m2. These results indicate that Mo surface is more easily wet by the CZTS slurry than the glass surface. A simple 2-D numerical model was developed to simulate the static wetting. The model indicates that the wettability of the surface can be increased by reducing the surface tension through surface modification, meaning a partially-wetting material such as glass can be become completely wetting. This was experimentally verified by adding a SWNT or metal film to the glass substrate. Additionally, the wettability between the CZTS slurry and the substrate can be controlled by changing the equilibrium of wetting through modifification of the CZTS slurry composition.
In order to investigate the effect of wettability on the quality of deposited thin films, surface roughness and morphology of CZTS films deposited on various substrates were characterized using AFM and SEM. Consistent with expectation, smoother films were found for surfaces with higher wettability. These results will provide valuable guidance for the solution-processed deposition of hydrazine-based CZTS thin films.

The spreading of a liquid on a solid surface, also known as wetting, usually takes place isotropically. However, if a surface can cause wetting to occur in certain specific directions only, benefits such as reduction in drag forces can arise. This has important implications for applications in the field of microfluidics, biosensing etc. and is the reason behind the heightened interest in surfaces that can produce directional wetting in recent years. Previous attempts at engineering surfaces that can induce directional wetting had mainly focused on the use of structurally anisotropic micro-/nano-structures such as bent or slanted nanowires. In this study, it is shown that directional wetting can also be achieved with nanoscale surface energy anisotropy. This surface energy anisotropy was generated by depositing a metal at an oblique angle onto an array of polymeric nanostructures fabricated with laser interference lithography and plasma etching. Because the polymer is more hydrophobic than the deposited metal, each nanostructure in the array had a face that was more hydrophilic than the other. When a water droplet was placed on such a surface, it was always found to wet preferentially in the direction of the hydrophilic face. Depending on the shape of the nanostructure, which can be controlled by the fabrication process, wetting can be made uni-, bi- or tri-directional. A model is proposed to suggest the basis for directional wetting observed in this study and is validated against measurements of contact angles and spreading anisotropy displayed by the droplet. The insights obtained in this study contribute to the understanding of wetting on heterogeneous surfaces and expand the capability of researchers to engineer functional surfaces for the control of wetting directions.

Microscale Polymethyl Methacrylate (PMMA) pillars with different height, spacing and molecular weight (MW) were fabricated on a quartz crystal microbalance (QCM) surface using nanoimprinting lithography (NIL) technology with Polydimethylsiloxane (PDMS) as the molding material. The patterned surfaces were treated with oxygen plasma and POTS (Perfluorinated Octyl Trichlorosilane) vapor to modulate surface wettability. The wettability of micropillars was initially characterized by contact angle measurement. Thereafter, a technique using laser scanning confocal microscope (LSCM) with immersion lens was developed to accurately measure the interface between pillars and liquid. The QCM impedance spectra for different water-micropillar interactions were obtained and correlated with their respective hydrophobicity and pillar parameters. Water was found always in the Wenzel state (fully penetrating) for micropillars of low height, and gradually shifts to the Cassie state (non-penetrating) with increasing pillar height and reduced pillar spacing. The results also show that hydrophobic surfaces in Wenzel state have similar responses to the hydrophilic surfaces while a significantly weaker response from QCM was found for the hydrophobic surfaces. Furthermore, the responses for hydrophobic surfaces are highly dependent on the height and spacing of micropillars, as well as the penetration depth of water. More importantly, the vibrating QCM surface results in micropillar vibration on the surface and, in turn, leads to changes in interactions between pillars and water. The effects of pillar height and molecular weight on surface hydrophobicity were studied in detail to clarify this interesting phenomenon.

Here we report a mussel-inspired, material-independent surface chemistry with controlled adhesive properties in a molecular-level for developing a platform to deliver the smallest therapeutic molecule, nitric oxide (NO). Poly(dopamine) (pDA) and poly(norepinephrine) (pNE) coating is both an emerging mussel-inspired surface functionalization techniques that can be applicable to a variety of materials regardless of their chemical environment of surfaces with its unique material-independent adhesion properties.[1,2] The surface modification mechanism of pDA and pNE are known as following the similar 5,6-dihydroxyindole (DHI) derivative chemical pathway,[3,4] and the secondary amine involved in DHI can be useful for an excellent NO-loading molecular platform. We prepared surface conjugated diazeniumdiolates groups (NO precursor) onto the secondary amines involved in the respective pDA or pNE layers, and the spontaneous dissociation of one diazeniumdiolates releases two molecules of NO gas molecules when water molecule is accessed to the surfaces.[5] We found that significant large amount of NO was attached and released from the pNE modified surface compared to pDA modified one. The difference in molecular adhesion of NO precursor is arising from the existence of a unique by-product called 3,4-dihydroxybenzaldehyde (DHBA), unavoidably generated during the pNE surface functionalization. DHBA can interact with NE by Schiff-base formation followed by auto-reduction of imine bond, resulting DHBA-NE dimer. This key leads to the nanoscale-smooth coating morphology of pNE, which can be a big advantage over pDA, especially in applications involving nano-scale substrates. Not only for controlling the morphology, the integration of DHBA-NE on pNE coating layer is essential that additional secondary amine involved in DHBA-NE can generate an excess amount of NO-loading molecular platform for NO storage and delivery, which can be potentially useful for biomedical applications.
[1] H. Lee, S. Dellatore, W. Miller, P. B. Messersmith, Science 2007, 426-430.
[2] S. M. Kang, J. Rho, I. S. Choi, P. B. Messersmith, H. Lee, J. Am. Chem. Soc. 2009, 131, 13224-13225.
[3] S. Hong, Y. S. Na, S. Choi, I.-T. Song, W. Kim, H. Lee, Adv. Funct. Mater. 2012, 22, 4711-4717.
[4] M. d'Ischia, A. Napolitano, A. Pezzella, P. Meredith, T. Sarna, Angew. Chem., Int. Ed. 2009, 48, 3914-3921.
[5] S. Hong+, J. Kim+, Y. S. Na, J. Park, S. Kim, K. Singha, G.-I. Im, W. J. Kim, H. Lee, Angew. Chemie. Int. Ed. 2013, accepted, DOI: 10.1002/anie.201301646.

Nature is a great source of inspiration for creating unique structures with special functions. The representative examples of water-repelling surfaces in nature, such as lotus leaves, rose petals, and insect wings, consist of an array of bumps (or long hairs) and nanoscale surface features with different dimension scales. On the other hand, low optical transparency due to the Mie scattering from micro-roughness with different dimension scales has recently been considered as a crucial issue for recent interest in as eye glasses, solar cell panels and car windows which need both transparency and superhydrophobic property. Herein, we introduced a method of realizing highly transparent multi-dimensional hierarchical structures inspired by termite wings along with water-repellancy of the surfaces with different drop impact scenarios. The multi-dimensional hierarchical structures were fabricated by soft imprinting method with TiO₂ nanoparticle pastes. In order to achieve the enhanced hydrophobicity, fluorinated moieties were adsorbed to the patterned surfaces to lower the surface energy. As a result, super-hydrophobic surfaces (above 176° in water contact angle with a hysteresis less than 2°) with high transparency (above 90 % in transmittance) in visible region were realized. Moreover, it has been shown that UV light was effectively blocked by TiO₂ and different dyes were also easily incorporated inside the mesoporous structure, resulting in photocromic functional films.

Stainless steel is widely known corrosion resistant metal. Its resistance to corrosion and staining makes it an ideal material for many applications such as architecture, industrial establishments and medical instruments. The corrosion resistance of stainless steel comes from sufficient chromium to form a passive film of chromium oxide. With its intrinsic corrosion resistance, the wettability of metal surface is also important property which depends on the chemical compositions and geometrical microstructures. Even though the fabrication of superhydrophobic surface has been researched for a long time, it is difficult to fabricate an engineering superhydrophobic surface on stainless steel due to the chemical degradation of surface and its difficulty to fabricate microstructure on the surface. Recently, superhydrophobic surfaces on stainless steel have been studied by sol-gel coating, dip-coating, electroless plating, Teflon-like coating with plasma and laser machining. The structure made by etching method is sturdy while coated films can be fallen off from the stainless steel substrate. With laser machining, very small structure can be fabricated but it is not cost effective due to its high cost and low throughput.
In this study, a method was developed to fabricate a superhydrophobic surface on stainless steel. Chemical wet etching and electrochemical etching were used to make nano scale roughness and micro structure on the surface. FeCl3 which is generally used as an etchant for stainless steel was used for chemical wet etching. Electrochemical etching process uses electrochemical reaction at the interface between metal and electrolyte. With this process, it is possible to fabricate micro structure without burr on the surface and to control the dimension of structure. SAM (self assembled monolayer) method was also used to deposit hydrophobic layer on the micro/nano hierarchical structure. A low surface energy of SAM layer on the structure makes the surface superhydrophobic. The fabricated stainless steel was analyzed by FE-SEM, 3D-profiler and FT-IR spectrometer. The characteristics of superhydrophobic surface were analyzed by measurements of the static/dynamic contact angle and sliding angle.
The superhydrophobic surface of stainless steel has been successfully developed with hierarchical structure and liquid SAM coating. The effect of dimension to hydrophobicity of metal surface was calculated with different microstructure which has various pattern size and pitch.

The development of multilayer thin films with nanopores containing biomolecules has attracted much attention in material and surface science as one of the optical applications and surface wettability control via LBL (Layer-by-Layer) self-assembly method. Also, chitin nanofibers (CHINFs) have attracted much attention because of their high mechanical strength. The shells of crustaceans are expected to be particularly useful for materials applications, because they are made from mineral salts, protein, and chitin; it is known that mineral salts can be removed using HCl, and proteins can be removed using NaOH. The CHINFs surface is transformed from chitin to chitosan by deacetylation, which results in a positive charge on the CHINFs, due to the presence of amine groups. In this study, we fabricated antireflective film with nanopores for robust functional surface composed bio-based polymer and added hydrophobic performance by gas-phase process. To fabricate a low refractive index film, therefore, porosity was introduced into a thin film. The porous thin film was obtained by increasing the number of airspaces inside the membrane. Then, by depositing the deacetylated CHINFs, Poly (acrylic acid) (PAA) and SiO2 nanoparticles using the LBL method, the lower refractive index layer was fabricated. (CHINFs/PAA) films indicated that the highest transmittance was 96% and the lowest refractive index was 1.29. The transmittance decreased by only 1.3% after abrasion of 200 g/cm2 with cotton. (CHINFs/SiO2) films showed that the highest transmittance was 97% and the lowest refractive index was 1.20. After adding hydrophobic performance by gas-phase process, the film indicated that the highest transmittance was 97%, the lowest refractive index was 1.23 and the water contact angle is 153°. In addition, we fabricated transparent SLIPS (Slippy Liquid Infused Surface) film by putting a drop of lubricant oil (Krytox 103) on the films and the highest transmittance of this SLIPS film was 98%.

Polymers bearing azobenzene functionality have been gaining increasing attention because of their ability to alter physical properties or create mechanical action of bulk polymers in response to changes in environmental conditions. Generally, azobenzenes are attached to the side chains of polymeric precursors followed by casting to generate thin films for further studies. Our approach presented here differs from the previous works in that it utilizes self-polymerization of hydroxyl and/or acrylate functionalized azobenzene moieties and assembly of stimuli-responsive materials using electrospinning technique. We hypothesize that increased surface area and porosity of electrospun nanofibers of azobenzene functionality will greatly improve the photomechanical response factor of the resulting materials. The polymerization reaction was carried out without using a crosslinker in inert atmosphere at 70 °C for 24 hours. Reaction progress and the product was monitored using 1H NMR. The resulting polymer was then dissolved in DMF at approximately 75% wt% which was determined to be have the ideal viscosity for electrospinning. The dissolved polymer was loaded into a syringe and electrospun with an applied voltage of 15kV at 2 mu;L/m for 30 minutes. The resulting deep orange mat exhibits reversible changes in hydrophobicity and color when exposed to 365 nm light. The resulting materials were examined using TGA, DSC, 1H NMR, wettability , viscosity, and gel chromatography.

Interfaces between metal and metal oxides are encountered in several applications, including surface protection, catalysis and electronics. In each one of these applications, the interfacial mechanical strength plays a decisive role in the stability and reliability of the systems. However, there are several factors that affect this property including interfacial composition, atomic level structure and processing conditions (temperature and pressure). Several theoretical and experimental methods have been developed to determine the interfacial mechanical strength. Among the theoretical methods, density functional theory (DFT) is a popular technique in the calculation of the work of separation (W_sep) of metal-metal oxide interfaces. However, DFT only provides information at 0 K situations, which implies that the direct quantitative comparison of the computed results with the experimental W_sep is not always possible.
In this work, we used DFT methods to calculate the W_sep of the Pt-HfO₂ interface at different interfacial O coverages (0, 0.25, 0.5, 0.75 and 1 OML) and several cleavage planes of the heterostructure. Using first principles thermodynamics, we combined the information of the lowest W_sep of the Pt-HfO₂ system for different O configurations and propose a parameter-free method to determine the average work of separation as a function of temperature and O pressures. The average work of separation obtained for the Pt-HfO₂ heterostructure is in excellent agreement with the experimental value reported in the literature, measured at high temperatures and low O pressures. The methodology used in this work can be extended to different metal-metal oxide interfaces to determine the adhesive properties as a function of temperature and pressure.

In recent years, nanocomposite materials fabricated by metal nanoparticles (NPs) and thin metal nano-grained films deposited on or embedded in soft polymeric substrates have emerged in the developing nanotechnonolgy applications (i. e. organic transistors, light-emitting diodes, solar cells etc.). To generate metal NPs or nano-grained metallic films on or near a polymer surface, ion implantation, evaporation, and sputtering methods have been utilized. To precisely control the surface properties of polymer nanocomposite films, it is essential to understand how NPs interact with the surface. In the present work, we report on an atomic force microscopy study of the wetting, adhesion and embedding kinetics properties (as a consequence of the long-range mobility of the polymeric chains above the glass transition temperature), under thermal processes, of Au and Ag NPs sputter-deposited on two amorphous soft polymeric layers: poly(methyl methacrylate) (PMMA) and polystyrene (PS). We studied in details the embedding process as a function of the annealing temperature and time so to evaluate the embedding rate both for Au and Ag in PMMA and PS. Also the NPs embedding statistics was studied analyzing the number of the embedded NPs as a function of the annealing time. The quantification of all these parameters, allow us to propose the embedding mechanism of deposited metal NPs on soft polymeric films, as an effective way to generate, in a controlled way, metal/polymer nanocomposites.

Since the creation of the Lifshitz theory of van der Waals-London dispersion (vdW-Ld) forces, accurate knowledge of dielectric response functions has been the key requirement for reliable computation. The connections between material properties, their processing into a form appropriate for computation, and -most important- the propagation of spectral details into specifics of vdW-Ld forces have no general solutions. They must, necessarily, be carefully recognized case-by-case for different materials, media, and geometries. Among the many electronic properties requiring careful attention are excitonic many-body effects for which it is not clear how the changes in optical spectra will affect the overall magnitude of the vdW-Ld interaction between materials.
Excitonic effects in low-dimensional systems, such as graphene and carbon nanotubes, tend to introduce additional absorption peaks in the energy range below 5 eV and to shift slightly the positions of some other peaks. An important question in this respect is how the changes in optical spectra due to excitons affect the overall Hamaker coefficients and the trends in the vdW-Ld interaction between different materials. Because the vdW-Ld interaction is non-local in frequency, being a functional (or more precisely a discrete sum over the Matsubara frequencies) of the frequency-dependent dielectric response, it is reasonable to expect that the interaction will depend more on the global properties of the dielectric response set by sum rules rather than on specific details of spectra.
A related problem is connected with refractive index-matching, sometimes used to modify the inter-particle interactions through their vdW-Ld component. In the index-matching method, one assumes that the vdW-Ld interaction stems only from the optical frequency regime; if this part of the spectra of interacting bodies and the intervening medium is made to coincide, its contribution to the vdW-Ld interaction will vanish identically. Again, because of the non-local nature of the vdW-Ld interaction, one should expect that even for refractive-index-matched situations the vdW-Ld interactions will depend primarily on the global properties of the dielectric response and much less on the presence or absence of a specific peak.
We have embarked on a detailed investigation of how changes in the spectral properties of the dielectric response function over a finite interval of frequencies alter the strength of vdW-Ld interactions expressed as the corresponding Hamaker coefficient. We consider dielectric spectra that differ only by the presence or absence of a single (exciton) peak and observe the consequence of this difference on the Hamaker coefficient for the interaction of two planar semi-infinite regions. We analyze specifically the changes of all the Matsubara components to the interaction free energy in order to monitor the effect of the dielectric response variation on the vdW-Ld interaction energy functional.

Abstract:
Membrane Distillation (MD) is a thermally-driven separation process, in which only vapor molecules transfer through a microporous hydrophobic membrane [1]. In sea water desalination using MD, it is highly desired that the membrane structure has a low affinity for water, which requires the membrane to exhibit high hydrophobicity to minimize water adhesion [1]. The extensive use of PTFE (polytetrafluoroethylene) and PVDF (polyvinylidenefluride) in MD has raised the attention to their environmental impact due to membrane disposal. Due to its biodegradability and hydrophobicity, polylactic acid (PLA) is a potential candidate for MD desalination [2, 3]. In this study, PLA membrane is fabricated by electrospinning. The morphology of the membrane can be controlled by adjusting the electrospinning process parameters and by applying post-heating treatments. Furthermore, the thickness of the membranes and the presence of beaded fibers, fused fibers and porous fibers can be adjusted. The morphology of the obtained membrane is investigated by means of scanning electron microscope. The static and dynamic contact angle (CA) is measured by sessile drop technique with water as the probe liquid. To enhance the hydrophobicity of the PLA membrane and obtain improved water repelling properties, a fluorinated silane (trichloro(1H,1H,2H,2H-perfluorooctyl)silane) is coated on the membrane under modest vacuum (asymp;10 kPa) by vapor deposition. The treated membranes are found to have unaffected morphology and structural characteristics and higher CA compared with those of the untreated membrane. Thus treating membranes of different thickness and morphology with fluorinated silane yields even higher hydrophobicity[4] which can be favorable for applications like anti-wetting and self-cleaning, etc. Meanwhile, keeping in mind that CA measurement only yields the macroscopic hydrophobicity characteristics of the membrane, the microscopic water repelling property inside the pores in the membrane is investigated by means of force spectroscopy in atomic force microscopy (AFM) [5].
References:
1. Alkhudhiri, A., N. Darwish, and N. Hilal, Membrane distillation: A comprehensive review. Desalination, 2012. 287: p. 2-18.
2. Gross, R.A. and B. Kalra, Biodegradable polymers for the environment. Science, 2002. 297(5582): p. 803-807.
3. Li, L., R. Hashaikeh, and H.A. Arafat, Development of eco-efficient micro-porous membranes via the electrospinning and annealing of poly (lactic acid). Journal of Membrane Science, 2013.
4. Buruaga, L., et al., Production of hydrophobic surfaces in biodegradable and biocompatible polymers using polymer solution electrospinning. Journal of Applied Polymer Science, 2011. 120(3): p. 1520-1524.
5. Santos, S., et al., Measuring the true height of water films on surfaces. Nanotechnology, 2011. 22(46): p. 465705.

In this work, we investigate the effect of various surface treatments on the bonding performance of initiated chemical vapor deposition (iCVD) polyglycidylmethacrylate (PGMA) thin film adhesives.
iCVD is a conformal, solvent-less, vapor phase polymerization and deposition technique that eliminates surface tension effects related to solvent phase processing. Moreover, iCVD has several advantages compared to traditional vapor-phase polymerization techniques like plasma-enhanced chemical vapor deposition (PECVD) and hot-wire chemical vapor deposition (HWCVD). It is a low-energy technique that results in higher retention of polymer functional groups compared to high-energy PECVD and HWCVD processes. Furthermore, iCVD has minimal influence on the substrate chemistry, unlike PECVD which involves constant bombardment of surface with high-energy ions.
The gas-phase processing, substrate compatibility, and retention of reactive group functionality, enable use of iCVD-PGMA films as thin film adhesives. In semiconductor processes potential applications include thermo compression bonding for wafer thinning, 3D integration, and packaging of MEMS/ NEMS devices. In preliminary work we studied iCVD-PGMA for use in 300 mm silicon wafer bonding and characterized the adhesion properties using a four point bending technique. We noted that the bond failure was primarily adhesive in nature, indicating the polymer-silicon interface was the weakest link. Altering the surface chemistry should allow manipulation of the adhesion properties to enable both permanent and temporary wafer bonding. This lead to the work presented here, which investigates the influence of surface treatment on iCVD-PGMA/substrate adhesion strength.
Wafer bonding was accomplished by thermocompression above the glass-transition temperature (60 °C) for iCVD PGMA. Subsequently an anneal step between 90-175 °C was performed. The surface property of Si was manipulated by molecular vapor deposition (MVD) of amine, epoxide, alkane and fluoro-terminated silanes with untreated and plasma treated substrates as control. The epoxide groups on PGMA function as anchoring points to graft polymer chains to amine and epoxide silanes under moderate conditions where result indicated improved bond strength at increasing temperature. Furthermore, iCVD PGMA films bonded with hydrophobic fluoro-silane modified surfaces lead to reduced adhesion strength. The bond interface was investigated using scanning acoustic microscopy which showed excellent bond qualities with up to > 98% bond area. iCVD PGMA films were successfully demonstrated as thin film adhesives for 300mm Si wafer bonding where the adhesion strength can be manipulated to enable permanent and temporary wafer bonding applications.

We present an approach to create fully transparent, omniphobic surfaces with remarkable liquid repellency properties by a bioinspired design mimicking the slippery surface of Nepenthes pitcher plants referred to as slippery liquid-infused surfaces (SLIPS).[1] In contrast to the lotus effect that inspired the design superhydrophobic surfaces by introducing roughness features to create a solid/air composite surface that enables liquid droplets to roll off with ease, our design is based on the creation of a fluid/fluid interface between a lubricant firmly locked into a porous surface structure and a non-miscible liquid to be repelled. If properly held in place, the lubricant itself then acts as the repellent surface. The exchange from a solid/liquid to a liquid/liquid interface effectively eliminates pinning points and leads to super-repellent surfaces with extremely low contact angle hysteresis and sliding angles (i.e. the minimum tilting angle required for a drop to slide off the substrate) - even for liquids with low surface tensions. Additionally, the fluid nature of the interface inherently possesses self-healing characteristics as the lubricant can wick back into damaged parts of the surface.
We introduce a transparency and damage tolerant coating based on lubricant infusion coating by applying colloidal monolayers to structure the surface and create the roughness necessary to support stable SLIPS conditions.[2] The small size of the colloidal nanostructures does not interfere with the optical properties of the substrate material and enables the design of fully transparent surfaces with remarkable wetting characteristics. We show that such surfaces repel various liquids, possess superior transparency, are self-healing and tolerate mechanical damage, are stable over extend periods of time, prevent adhesion of liquid-borne contaminants, including blood serum proteins and drastically reduce the adhesion of ice. The highly ordered structure of the coating enables us to understand and predict the stability or failure of repellency as a function of lubricant layer thickness and defect distribution based on a simple geometric model. The method can be applied to curved substrates and to photolithographic processes to pattern the repellent parts of the substrate, thus opening opportunities to spatially confine low surface tension liquids or complex fluids as blood.

[1] T.S. Wong, S.H. Kang, S.K.Y. Tang, E.J. Smythe, B.D. Hatton, A. Grinthal, and J. Aizenberg, Nature 2011, 477, 443
[2] N. Vogel, R. Belisle, B. Hatton, T.S. Wong and J. Aizenberg, Nature Comm., accepted for publication

Developing adaptive systems that can reversibly change one or more properties in response to external stimuli not only generates fundamental insights into the relationship between microscopic structures and macroscopic functions, but also has immense technological relevance in diverse areas from creating dynamic interfaces with biological tissues to designing energy-efficient buildings. Recent efforts to mimic biological adaptive systems have led to the design of hierarchical multicomponent hybrid composites that are made responsive by introducing an active material into a multiscale architecture. While existing materials can change individual properties such as wetting, adhesion or friction separately, no existing material platform can combine all three switchable properties in a single material. Here we show a topographically responsive composite made by infiltrating a porous matrix with colloidal dispersions of magnetic nanoparticles or ferrofluid, and demonstrate how a unique multiscale coupling of magnetic and capillary forces reconfigures local surface topography and yields dynamic wetting and switchable adhesive and frictional properties, as well as the abilities to remotely control fluidic pumping, transport and mixing. We provide physical insights into the mechanism of these magnetically actuated properties and functions. We envision our new dynamic surfaces would not only offer opportunities to study fundamental phenomena such as fluid transport on topographically responsive surfaces, but also find applications in areas such as microfluidics, responsive coatings, and dynamic material interfaces with cells and tissues.

We report highly-sensitive measurements of pressure-induced water infiltration into hydrophobic nanostructured surfaces using transmission small angle x-ray scattering. We have developed new methods of patterning arbitrarily-large area nanostructured surfaces with ~10nm feature size and ~10^10/cm^2 feature density by combining block-copolymer self assembly and plasma-based etching. Control over processing conditions allows us to generate uniform surfaces of posts, lamellae, or tapered cones in order to relate the water infiltration characteristics to the nanotexture geometry. We study details of water penetration into the nanostructures under controlled hydrostatic pressure, determining the infiltration filling fraction from the intensity of the diffracted signal. In all structures, significant infiltration occurs irreversibly above a critical pressure depending on the texture size and geometry. We present the details of the infiltration isotherms, which are well modeled by accounting for the specific shape of the nanotexture's geometry.

The ability to control liquid behaviour at surfaces is highly relevant for a number of application areas, including for example the performance and reliability of inkjet nozzles. Generally, the wettability of solid substrates can be modified both by morphological micro- and nanostructuring as well as by chemical functionalization. We investigate the potential of chemically defined patterns consisting of hydrophobic self-assembled monolayers (fluoroalkylsilane) on hydrophilic (pristine SiO2) substrates to control dynamic liquid behaviour on morphologically flat surfaces.
We review our results on anisotropic spreading and evaporation of droplets on such chemically striped surfaces. The equilibrium shapes of asymmetric droplets, arising from patterns of alternating hydrophilic and hydrophobic stripes with dimensions in the low-micrometer range, are investigated in relation to the stripe widths. Owing to the well-defined small droplet volume, the equilibrium shape exhibit unique scaling behaviour. Additionally, high-speed camera measurements reveal the importance of kinetics involved in the formation of the asymmetric droplets. Similarly, evaporation of droplets on such surfaces also exhibits a directional anisotropy.
We also present experiments investigating the motion of the liquid from surface areas with low macroscopic wettability towards areas with a higher wettability. The density of self-assembled fluoroalkylsilane monolayers as defined by the chemical pattern proves to be of paramount importance. Both linear and radial patterns are presented, which induce liquid movement across chemically defined gradients in surface energy.
To provide a benchmark for the analysis of our results, we use two different numerical tools. In the first method the minimum energy state of a droplet on a chemically striped patterned surface is determined using Surface Evolver. Simulated results agree well with experiments of high viscosity liquids, while it does not match the result for low viscosity liquids, such as water. The effect of kinetic energy during deposition of a droplet on such a pattern will be discussed. In the limit of low kinetic energy, either by using a controlled way of depositing or by using highly viscous liquids, the droplet is close to the minimum energy state and the calculations for the minimal energy state match the experiments.
To enable modelling of dynamic behaviour of low viscosity liquids, we use the multicomponent multiphase lattice Boltzmann method (LBM). With this method it is possible to include actual dynamics of the droplet leading to different final shapes on the surfaces. The directional spreading behaviour is reproduced including the contribution of kinetic effects, and also the anisotropic evaporation characteristics emerge from the simulations. Finally, the LBM simulations also allows investigation of the gradient-induced motion, enabling straightforward modification of pattern designs prior to their actual fabrication.

We discuss recent numerical results, based on a lattice Boltzmann solution of a hydrodynamic phase field model, investigating how drops roll and bounce on superhydrophobic surfaces.

Recent years have witnessed intense interest in multifunctional surfaces that can be designed to switch between different functional states with various external stimuli including electric field, light, pH value, and mechanical strain. The present paper is aimed to explore whether and how a surface can be designed to switch between superhydrophobicity and superhydrophilicity by an applied strain. Based on well-established theories of structure buckling and solid-liquid contact, we show that this objective may be achieved through a hierarchically wrinkled surface. We derive general recursive relations for the apparent contact angle at different levels of the hierarchical surface and investigate the thermodynamic stability of different contact states. Our study may provide useful guidelines for the development of multifunctional surfaces for many technological applications.

Working equations that describe wetting phenomena can be derived in a variety of ways, by starting from capillary forces, Laplace pressure, or solid surface energies. We examined the relative importance of the contact line and interfacial areas in the capillary rise inside small diameter glass tubes. A series of simple experiments demonstrate that this wetting phenomenon is controlled by interactions in the vicinity of the contact line.

Liquid dielectrophoresis (L-DEP) allows a bulk force to be applied to a dielectric liquid using a non-uniform electric field. In our work we have developed a method using surface fabricated interdigitated electrodes whereby the effects of L-DEP can be localized to the liquid-vapor or solid-liquid interfaces. In the first case, which applies to thin films of liquid, this allows the liquid surface to be shaped and a voltage programmable diffraction grating to be created.¹ In the second case, which applies to droplets with a thickness greater than the decay length of the electric field, this allows the equilibrium contact angle to be controlled in a similar manner to electrowetting.² The ability to adjust the final equilibrium contact angle by choosing a voltage also creates the possibility of performing dynamic contact angle measurements over a full range from partial wetting to complete wetting on the same substrate.³ In this work we describe a modified Hoffman-de Gennes law for the edge speed-contact angle dependence and derive a theory for the dynamic spreading of droplets that predicts three regimes depending on whether the applied voltage is below, at or above a threshold voltage for complete wetting. These three regimes are: i) an exponential approach to a finite equilibrium contact angle, ii) a (Tanner&’s) power law approach to complete wetting, and iii) a superspreading regime The characteristic times for partial wetting and the exponents for spreading and superspreading are derived for both axisymmetric droplet spreading and the spreading of stripes. Experimental results for the spreading of stripes of 1,2 propylene glycol are found to be in good agreement with the theory in all three regimes. This approach provides an alternative to the use of surfactants for the study of superspreading.
We acknowledge funding from the UK EPSRC (EP/E063489/1). NS acknowledges funding from Nottingham Trent University.
¹Brown, C. V., Wells, G. G., Newton, M. I., McHale, G. (2009). Voltage-programmable liquid optical interface. Nature Photonics3, 403-405.
²McHale, G., Brown, C.V., Newton, M.I., Wells, G.G., Sampara, N. (2011). Dielectrowetting driven spreading of droplets. Phys. Rev. Lett.107, art. 186101.
³McHale, G., Brown, C. V. and Sampara, N. (2013). Voltage induced spreading and super-spreading of liquids, Nature Communications4, art. 1605.

Non-wetting surfaces containing micro/nanotextures impregnated with lubricating liquids can exhibit remarkable non-wetting properties and robustness compared to superhydrophobic surfaces that rely on stable air-liquid interfaces. In this talk, we examine the fundamental physicochemical hydrodynamics that arise when droplets, immiscible with the lubricant, are allowed to move along these surfaces. We find that these four-phase systems show novel contact line morphology comprising a finite annular ridge of the lubricant pulled above the surface texture and consequently as many as three distinct 3-phase contact lines. Depending on the spreading coefficients, the lubricant film can completely cloak the droplet, which can have important consequences for lubricant longevity and phase transitions. We show that these distinct morphologies not only govern the contact line pinning that controls droplets' initial resistance to movement but also the level of viscous dissipation and hence their sliding velocity once the droplets begin to move. Additionally, these unique four-phase systems can have up to three different 3-phase contact lines, giving up to 12 different thermodynamic configurations, which we describe in a thermodynamic regime map. Next we examine phase transitions such as condensation and freezing on these surfaces. By examining the microscopic characteristics in an Environmental SEM (ESEM) we obtain insights on the nucleation and growth processes, which are significantly influenced by the spreading characteristics of the lubricant. On surfaces optimized for condensation we find that condensate droplets smaller than 100 mu;m become highly mobile and move continuously at speeds that are several orders of magnitude higher than those on identically textured superhydrophobic surfaces. This remarkable mobility produces a continuous sweeping effect that clears the surface for fresh nucleation and results in enhanced condensation. In the case of frost formation, we find that lubricant spreading onto the growing ice can lead to depletion of lubricants from the surface, which can potentially compromise the icephobic properties of the surface. Given these findings, we conclude that lubricant-impregnated surfaces need to be carefully designed in order to deliver optimal non-wetting properties.

Learning from nature and starting from the superhydrophobic lotus leaves, we revealed that a super-hydrophobic surface needs the cooperation of micro- and nanostructures. Further studies have proved that the arrangement of micro/nano structure can directly affect the wettability and water movements. Recently, we found that hydrophilic compositions together with micro/nano structures endow the fish scale with superoleophobicity underwater. Inspired by this, artificial fish scales with robust mechanical strength have been fabricated.
Based on the micro/nano structured interfaces with special wettability, kinds of basic chemical reactions could be done within a small water drop. Crystal arrays could also been prepared, and also small molecule, polymer, silver NPs and microspheres can be arrayed in one direction.
Under certain circumstances, a surface wettability can switch between superhydrophilicity and superhydrophobicity. Besides the 2D interface, we recently extended the cooperation concept into 1D system. Artificial ion channels with smart gating properties have been fabricated by integrating smart molecules into the single nanochannels. These intelligent nanochannels could be used in energy-conversion system. The other one dimensional system is the artificial spider&’s silk. The periodic spindle knots on the spider&’s silk can drive liquid drops in a specific direction that can collect water from moist air. Further, we prepared artificial spider&’s silk and droplets of water on the artificial spider&’s silk behaved similarly to those on its biological counterparts. Most recently, inspired by the cactus surviving in the most drought desert, we probed into the relationship of the structure-function of cactus and found that the cactus had evolved a multi-structural and multi-functional integrated continuous fog collection system.
Learning from nature, the constructed smart multiscale interfacial materials system not only presents new knowledge, but also has great applications in various fields, such as self-cleaning glasses, water/oil separation, anti-biofouling interfaces, and water collection system.

The terms “ultrahydrophilic” and “superhydrophilic” were defined in 1996 for UV-irradiated TiO2 coated glass surfaces displaying contact angles theta; < 10° [1]. Ultra-/superhydrophilic metallic biomaterials were reported by us in 2001 [2]. However the phenomenon of superhydrophilicity is still poorly understood and lacks a consensual definition [3,4]. This appears due to the fact that measurements of hydrophilicity are impaired by the zero degree limit of the Young equation. Even if higher wettabilites are obtainable, dynamic contact angles for cos theta; > 1.0 are classed as “undefined”. It was found, that the dogma stating cos theta; > 1.0 as undefined" is false. The solution is to extend hydrophilic dynamic contact angles into imaginary number space (Θ), with this wettability termed as “hyperhydrophilic” [3,4]. Thus the “Lotus Effect” found on rough surfaces on the hydrophobic side of the wettabilty scale is now complemented by the “Inverse Lotus Effect” (i.e. “roughness induced hyperhydrophilicity”) on the hydrophilic side of the scale [3,4]. Examples for extending the analysis of wettability beyond the superhydrophilic into the hyperhydrophilic range will be shown for medicinal titanium surfaces [5,6] with roughness values (Ra) between 3-30 µm yielding advancing and receding imaginary contact angles in the range of Θ ~ 2i°-20i°. On the application side it has been shown that endosseous titanium implants with hyperhydrophilic surfaces result in an enhanced osseointegration in the sheep rib [7].
[1] Hayakawa, M., Kojima, E., Norimoto, K., Machida, M., Kitamura, A., Watanabe, T., Chikuni, M., Fujishima, A., Hashimoto, K., & Itoh, H. (1996) PCT Publ.No. WO96/29375, pp. 1-112
[2] Jennissen, H.P. (2001) Ultra-hydrophile metallische Biomaterialien, [Ultra-hydrophilic Metallic Biomaterials]. Bionanomaterials (formerly: Biomaterialien), 2, 45-53.
[3] Jennissen, H.P. (2011) Redefining the Wilhelmy and Young Equations to Imaginary Number Space and Implications for Wettability Measurements. Materialwiss. Werkstofftech. (Mater. Sci. Eng. Technol), 42, 1111-1117.
[4] Jennissen, H.P. (2012) Hyperhydrophilic Rough Surfaces and Imaginary Contact Angles. Materialwiss. Werkstofftech. (Mater. Sci. Eng. Technol), 43, 743-750.
[5] Lueers, S., Seitz, C., Laub, M., & Jennissen, H.P. (2013) On the Utility of Imaginary Contact Angles in the Characterization of Wettability of Rough Medicinal Hydrophilic Titanium. In Advances in Contact Angle, Wettability and Adhesion., Vol. 1, (Mittal,K.L., ed), pp. 155-172. Wiley-Scrivener, Salem, MA.
[6] Lueers, S., Laub, M., Kirsch, A., & Jennissen, H.P. (2013) Large Scale Preparation and Analysis of Hyperhydrophilic Dental Implants with µSLA Titanium Surface. Biomed. Tech. (Berl), 57, in print.
[7] Lueers, S., Lehmann, L., Laub, M., Schwarz, M., Obertacke, U., & Jennissen, H.P. (2011) The Inverse Lotus Effect as a Means of Increasing Osseointegration of Titanium Implants in a Gap Model. Bionanomaterials (formerly: Biomaterialien), 12, 34.

The dynamic contact angles of Newtonian and non-Newtonian fluids were measured on both hydrophobic and superhydrophobic surfaces using a modified Wilhelmy plate experiment. For the Newtonian case, water and aqueous solutions of low molecular weight polyethylene oxide solutions were studied in order to vary the liquid&’s viscosity. For the viscoelastic case, a series of solutions of high molecular weight polyacrylamide solutions were studied with varying relaxation time and viscosities. The Wilhelmy plates consisted of hydrophilic acrylic, hydrophobic Teflon, and an acrylic surface sprayed with a commercially available paint to make it superhydrophobic. In all cases, the advancing and receding contact angle were measured as a function of plate velocity, fluid viscosity and fluid elasticity. For the Newtonian fluids, the advancing and receding contact angle on the hydrophobic Teflon surfaces were found to obey the expected scaling trends with capillary number. Specifically, costheta;_s - costheta;_d ~ Ca^2/3. The response of the dynamic contact angle on the superhydrophobic painted surfaces was quite different. The advancing contact angle was not found to change with velocity, but remain constant at theta;_a =160°. More interesting, the receding contact angle on the superhydrophobic surface was found decay with increasing capillary number while obeying a new scaling relation, costheta;_s,r - costheta;_d,r ~ Ca¹. The origins of this new scaling will be discussed. In addition, a series of viscoelastic solutions were formulated to investigate the role of elasticity on the dynamic contact angle. Measurements were performed on both hydrophilic and hydrophobic plates. Our measurements show that the dynamic contact angle depends not only on capillary number, but Weissenberg number as well.

The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing water vapor, and the contaminants are autonomously removed by the self-propelled jumping motion of the resulting liquid condensate, which partially covers or fully encloses the contaminating particles. The jumping motion off the superhydrophobic surface is powered by the surface energy released upon coalescence of the condensed water phase around the contaminants. The jumping-condensate mechanism is shown to spontaneously clean superhydrophobic cicada wings, where the contaminating particles cannot be removed by gravity, wing vibration, or wind flow. Our findings offer insights for the development of self-cleaning materials. [K.M. Wisdom et al, PNAS, vol. 110, pp. 7992-7997 (2013).]

The goal of this work is to study the key parameters affecting water droplet movement on a metallic substrate due to an underlying surface tension gradient and the effects that micro-structural roughness and anisotropic surface wettability have on water drainage. In air-conditioning applications, current research has already shown the tremendous potential of using surfaces that exhibit improved condensate management. This benefit arises because water retention on the air-side surface of metallic heat exchangers can reduce the air-side heat transfer coefficient, increase core pressure drop, and provide a site for biological activity. In refrigeration systems, the accumulation of frost on metallic fins requires periodic defrosting and reduces energy efficiency. When water is retained on these surfaces following the defrost cycle, ice is more readily formed in the subsequent cooling period, and such ice can lead to shorter operational times before the next defrost is required. Thus the management and control of water droplets on heat-transfer and air-handling surfaces is vital to energy efficiency, functionality, and maintenance of air-cooling systems.
Despite the proliferation of surface wettability research over the past few decades, the author is not aware of any published work that has successfully created a surface tension gradient using topography alone (i.e. no chemical coating) to move water droplets in a preferred direction along a metallic surface, with the goal of using those gradients to improve condensate distribution and drainage. With respect to this aim, we recently demonstrated the promise of this idea by creating a gradient in copper that resulted in water droplet movement of 1-2 mm along a horizontal plane— something that (to the best of our knowledge) had never been demonstrated before on a metallic surface without the use of chemistry. To date, however, only a single gradient pattern has been studied and no optimization has been performed. In this work, additional surface tension gradient patterns will be studied including radial and triangular designs. These patterns will be created using either laser etching or metal deposition techniques. The use of a hydrophobic self-assembled monolayer—namely, heptadecafluoro-1-decanethiol (HDFT)—will also be explored. The innovation of this research is the development and testing of novel, anisotropic surfaces that not only reduce water retention, but also facilitate the distribution of condensate droplets in preferred locations on the surface for the purpose of enhancing air-side heat transfer. Because heat exchangers are key components in many systems, both from a cost and performance point of view, it is expected that the fundamental science outcomes from this study could have a profound impact on many industries.

Dew (also called “Breath Figures” in the laboratory) is the dropwise condensation of water vapor on a substrate. In many regions of the world, dew water could serve as an additional water source, supplementing rain and fog water collection. An important concern is to improve water collection from the condensing surfaces. Wipers can be used, however it appears that natural wipers are present in the dew process. When one carefully observes the runoff of water drop condensing on windows in a room supersaturated with water vapor, one realizes that the drops mostly start to flow from the top edge of the window.
The detachment of droplets by gravity is a competition between gravity and contact line pinning forces. A drop will detach from an inclined surface when its diameter exceeds a critical size that depends on the inclination angle. In this event, the effect of boundaries seems thus to exhibit a special role in allowing the drop growing at an edge faster than in the middle of the surface.
The growth of droplets obeys general growth laws. A pattern of droplets of dimensionality D on a substrate of dimensionality d grows according to two mechanisms. (i) Nucleation and diffusive growth of individual drops with radius R_isim;(t/t₀)^α with α a growth exponent and t₀sim;F^-1/2p^-1 a typical growth time that depends on the water vapor flux F near the drops and the supersaturation p. (ii) Coalescence events, which rescale the growth, giving a mean radius <R_i>sim; (t/t₀)^β, with β = αD/(D-d). The exponent α depends on the shape of the concentration gradient around the drops. For a unique drop with a 3-dimensional vapor gradient, α = 1/2; for a surface gradient, α asymp; 1/3. The relative contribution of a surface or volume gradient depends on the thermal conditions inside the drop. However, when drops are in a pattern, they have to share the vapor gradients. It results a mean linear vapor profile, directed perpendicular to the surface, with the growth exponent α = 1/3.
Dedicated experimental investigation of droplet growth in a dew condensation chamber equipped with optical microscope and video camera shows that droplets obey the same growth law [<R_i>= At^β, with β asymp; 1] on edges, grooves, scratches and in the middle of the condensing surface. The prefactor A, however, is larger at the substrate edge than at the groove edge, itself larger than in the middle of the substrate. In contrast, A is lower inside the groove, close to the edge. The scratch gives very little effect. Drops near an edge thus grow faster because they collect more water vapor, experiencing less competing effects from the neighboring droplets than in the middle of the surface.

Controlled transport of aqueous volumes on surfaces with wettability patterns or gradients has strong relevance to engineering devices whose operation relies on dropwise condensation (e.g. heat exchangers and fog capture devices) or fluidic movement (lab-on-a-chip). An ideal surface for high-rate dropwise condensation should possess a large contact angle (to reduce solid-liquid contact area) and small contact angle hysteresis, so that the condensed droplets are highly mobile on the cooled surface, thus exposing fresh areas for further droplet nucleation and growth after droplets are swept away by gravity. However, this mechanism has two major limitations. First, droplet removal cannot take place on a horizontal surface. Second, the minimum droplet size for such removal, as designated by the capillary length, is ~2.7 mm for water. This large size leads to considerable delays for liquid removal by gravity, and a lowering of overall condensation heat transfer coefficient (the persisting liquid raises thermal resistance). Biphilic and super-biphilic [1] surfaces feature sharp wettability gradients —by creating spatial regions of high- and low-surface energy— on a heat transfer substrate. Ideally, dropwise condensation is favored on a superhydrophobic surface where the droplets form and grow due to further condensation and coalescence. However, sustained gravity-independent removal of the droplets from the superhydrophobic domains requires specially designed superhydrophilic channels, which drain the liquid through capillary forces. The smallest droplet size for drainage dictates the overall condensate removal rate; the smaller the size, the more efficient is the surface in removing the liquid. The dropwise condensation heat transfer rate depends on the wettability difference between the phobic and philic domains and their geometrical distribution on the substrate. The underlying physics can be unraveled by studying the transport dynamics of condensate droplets across sharp wettability steps. We fabricate and study large-area biphilic surfaces with alternate phobic and philic regions of prescribed size, shape and wettability jump for sustained capillary drainage of droplets from the phobic sections on the substrate. The dynamic motion of mm-sized droplets across phobic/philic boundaries of the substrate is visualized by high-speed imaging. The performance of the biphilic surfaces is quantified in terms of liquid removal rate and evaluated with respect to droplet size, surface energy differences and other salient geometrical parameters of the surface patterns. The results are used to optimize the surface engineering parameters for maximizing dropwise condensation and condensate removal rates.
1. A. R. Betz, J. Xu, H. Qiu, and D. Attinger, “Do surfaces with mixed hydrophilic and hydrophobic areas enhance pool boiling?,” Applied Physics Letters, vol. 97, p. 141909, 2010.

Wetting surfaces such as metals must be treated by a non-wetting modifier to yield dropwise condensation, but these hydrophobic promoters are often not durable in a steam environment. We report sustained dropwise condensation on an ultra-thin copolymer film grafted to a metal surface by initiated chemical vapor deposition (iCVD). These films exhibit low hysteresis under ambient conditions, and the diameter of departing drops during condensation is significantly smaller than seen on other hydrophobic surfaces such as gold ad a fluorinated silane layer. Using the low-power solvent-free iCVD method, we demonstrate how these copolymer films can be applied to complex geometries to lead to robust dropwise condensing surfaces with applications in power generation and desalination.

Icing on solid surfaces is commonplace in nature, technology and everyday life, bringing with it at times catastrophic consequences. Development of a passive, energy saving approach that exploits surface treatment or texturing to produce unfavorable icing conditions is of fundamental importance. Superhydrophobic surfaces, with micro- , nano-, or hierarchical roughnesses, have excellent water repellency marked by very high droplet contact angles (>150°). In addition, they also show low adhesion to water (characterized by low contact angle hysteresis) down to temperatures near and even below the freezing point. However, a rational framework for designing surfaces with predictable and extraordinary resistance to ice formation and adhesion remains a challenge. Here we introduce a thermodynamically-guided approach leading to surfaces with extremely long ice nucleation delay times combined with very low and robust nucleation temperatures. The classical nucleation theory of thermodynamics offers initial guidance on the design of an icephobic surface. For example, it predicts that nucleation is depressed on convex bumps of a nanoroughness and is promoted in concave nanoscale pits. As a consequence, the size and density of nanoscale pits on a surface should critically affect the nucleation temperature of a sessile supercooled droplet. The effect of the nanoscale pits explains the generally assumed trend of nucleation temperature increase for increasing nanoscale roughness. In this work, in a strong departure from the above plausible results of classic heterogeneous nucleation theory, we show that the presence of an interfacial quasiliquid layer on the ice in contact with a surface, counteracts the ice nucleation-promoting effect of nanoscale pits. We refer to this as interface confinement effect in the nanoscale pits. The confinement effect of the quasiliquid layer strongly suppresses the stable formation of ice nuclei. This critically important theoretical framework, guides our design and fabrication of nanostructured icephobic surfaces with extraordinaty nucleation suppression capability. These surfaces exhibited extremely low nucleation temperatures of ~-24 °C combined with extreme time delays in nucleation. The robustness in the value of ice nucleation temperature was demonstrated with the insensitivity of this temperature to roughnes RMS for over three orders of magnitude in RMS roughness (~0.1 to ~100 nm). Such nanotextures were also applied on top of micropillar structures to harvest the additional benefit from, high liquid repellency and low ice adhesion. The hierarchical morphology surfaces were tested around their nucleation temperatures to determine the time it took to freeze supercooled sessile droplets. When such surfaces, rated at -24 °C for immediate nucleation, were tested at a minimally higher temperature (-21 °C), they delayed the freezing of a sessile supercooled water droplet at the same temperature by a remarkable 25 hours.

The problems due to ice accretion and frost formation have been prevalent for decades in a number of systems including aircrafts, wind turbines and power lines. The state-of-the-art techniques are either inefficient or expensive making them challenging to apply in practical applications. The recent development in the field of lubricant-impregnated textured surfaces has offered an alternative to address this problem. This presentation will focus on the design of the texture and the lubricant used in these surfaces. Ice adhesion strength measurements and cryo-FIB/SEM imaging show the dependence of ice adhesion on the texture density. We report that the optimized lubricant impregnated surfaces perform better than the state-of-the art low-energy solid coatings in lowering the ice adhesion strength.

This presentation will explore the design and properties of a new type of layer-by-layer assembled polymer coating with zwitter-wettable behavior. A zwitter-wettable coating is capable of rapidily absorbing a large amount of non-freezing water from the vapor phase but appears to be hydrophobic when probed with water droplets. Since the water absorbed is in a non-freezing state, the coating exhibits anti-fog and anti-frost capabilities even when conditioned at sub-freezing temperatures and subsequently exposed to warm humid air. Under these conditions, typcial glass surfaces will experience extreme frosting. The coatings are fabricated from aqueous solutions of poly(vinyl alcohol) and poly(acrylic acid) at very specifc pH values. Subsequent thermal crosslinking renders the layer-by-layer assembled coating insoluble in water and more mechanically robust.

Ice formation and accumulation dramatically impact the efficiency and durability of industrial components and machines, can have very detrimental effects on wind turbines and airplanes and strongly affect power transmission lines during winter. In recent years many reports were published on using superhydrophobic surfaces as anti-icing coatings and by this decreasing ice adhesion as well as delaying frost formation. However, very little attention has been paid on the question how condensed water freezes on superhydrophobic surfaces. We report on the generation of superhydrophobic surfaces, which significantly delay the freezing of condensed drops under subzero conditions. The surfaces in our studies comprise an array of silicon nano-needles “nanograss”, coated with fluoropolymer monolayers. The fabrication process of nanograss is mask-free and only consists of a single dry etching step.
When the surface is cooled down below the dew-point temperature, water starts to condense on the surface and eventually forms drops in the Cassie state. The condensed drops spontaneously move on the surface due to release of surface free energy upon coalescence of two drops (so-called mobile condensation). Drop at the edge of the substrate jump off. This results in continuous water removal from sample and therefore considerably lower surface coverage with water if compared with condensation on surfaces possessing immobile condensation.
At subzero temperatures the freezing of condensed drops is mainly governed by heterogeneous nucleation mechanism. Here the ice embryo is preferably formed on water-solid contact area, which dimension determines the nucleation rate of the drop at certain conditions. The solid fraction of nanograss (i.e. the fraction of drop footprint in contact with the solid) was calculated to be 0,01%. Thus, low solid fraction combined with poor surface coverage with water, dramatically decrease the freezing probability at conditions leading to water freezing on hydrophobic surfaces or on surfaces with condensation of drops which are immobile.
As a result, the freezing experiments show that no freezing happened on the nanograss surface held at -10 °C in room environment (40% RH, 22 °C) even for up to 8 hours provided that freezing of sample edges could be neglected. However, when sample was cooled to -20 °C we observed several independent freezing events. This shows that despite the low solid fraction and poor surface coverage with water, the freezing temperatures are considerably higher than ones corresponding to homogeneous freezing. Ways to further improve the anti-freezing properties of surface might be further lowering the solid fraction of nanostructures and enhancing water removal from surface by tilting, shaking or exposing to continuous air flow.

Frost formation and accumulation on cold surfaces adversely affect the operational performance in aircrafts, refrigerators, wind turbines and power lines.[1,2] Engineering icephobic surfaces that can retard the frost formation and accumulation is of scientific and practical importance. Despite the promising potential in engineering icephobic surfaces, current materials are limited by the breakdown of their icephobicity in the condensation frosting environment. In particular, the frost formation over the entire surface is inevitable as a result of undesired inter-droplet freezing wave propagation initiated by the sample edges, which are associated with low heterogeneous frost nucleation energy barrier owing to their geometric singularity.[3,4] Moreover, without a rational design, the frost formation directly results in an increased frost adhesion, posing severe challenges for the subsequent defrosting process.[5, 6] Thus, an ideal icephobic surface should not only suppress the onset of individual droplet freezing and inter-droplet freezing wave propagation during the condensation frosting process, but also promote the efficient ice removal at the defrosting stage. Here, we report a hierarchical surface that is capable of removing condensate droplets before any heterogeneous ice nucleation could occur, retarding frost formation through the suppression of inter-droplet freezing propagation over the entire surface, as well as promoting frost removal efficiently by self-lubrication. We find that the enhanced performances are mainly owing to the activation of the microscale edge effect in the hierarchical surface, which increases the energy barrier for ice bridging as well as engendering the frost integrity and liquid lubrication during the defrosting process. We envision that the concept of harnessing surface morphology to achieve superior performances in two distinctively opposite phase transition processes (frosting/defrosting) might open up a new avenue for the development of efficient materials for various applications ranging from anti-icing, dropwise condensation and water harvesting.
1. Meuler, A. J., McKinley, G. H. & Cohen, R. E. Exploiting topographical texture to impart icephobicity. ACS Nano 4, 7048-7052 (2010).
2. Stone, H. A. Ice-phobic surfaces that are wet. ACS Nano 6, 6536-6540 (2012).
3. Boreyko, J. B. & Collier, C. P. Delayed frost growth on jumping-drop superhydrophobic surfaces. ACS Nano 7, 1618-1627 (2013).
4. Guadarrama-Cetina, J., Mongruel, A., González-Viñas, W. & Beysens, D. Percolation-induced frost formation. Europhys. Lett. 101, 16009 (2013).
5. Chen, J. et al. Superhydrophobic surfaces cannot reduce ice adhesion. Appl. Phys. Lett. 101, 111603 (2012).
6. Nosonovsky, M. & Hejazi, V. Why superhydrophobic surfaces are not always icephobic. ACS Nano 6, 8488-8491 (2012).

Zwitterionic chemistries have shown great potential as ultra-low fouling surface functionalities, which resist the adhesion of a large variety of molecules and organisms and maintain exceptional cleanliness in practical environments such as sea water, bacterial culture(1) or human serum(2). This resistance to surface adhesion originates from the extreme hydrophilicity of the zwitterionic moieties. Almost perfect wetting occurs when a zwitterionic surface is in contact with water(3). The replacement of surface-bound water molecules by foulants is enthapically unfavorable and thus the surface is anti-fouling.
The extreme hydrophilicity renders zwitterionic polymers soluble in water and therefore the incorporation of cross-linker is necessary to make zwitterionic coatings viable and applicable to various substrates. However, reduced hydrophilicity and impaired fouling resistance have been observed as results of cross-linking. Although the water uptake of a copolymer film is reduced only by 30-50% with 50% cross-linker content(4), the fouling resistance can be reduced to a much greater extent because of the surface chain reorganizations upon film casting(1). The hydrophobic segments introduced by cross-linker tend to migrate to the uppermost surface to minimize the interface energy during the casting in open air.
Here, we report a two-step synthesis scheme that produces surface-concentrated zwitterionic moieties with cross-linked and mechanically robust bulk films(1, 5, 6). A precursor film containing tertiary amine groups is deposited via initiated chemical vapor deposition (iCVD) using commercially available monomers. Then a reaction with 1,3-propanesultone is carried out under diffusion-limited conditions to convert tertiary amine to zwitterion. The diffusion-controlled conditions are the key to high surface concentration of zwitterionic moieties. This method allows for the tuning of bulk film properties independently of the surface fouling resistance. Virtually any surface can be rendered anti-fouling with this substrate-independent and benign method(7). Ultra-thin (30nm) zwitterionic coatings have been applied directly to the surfaces of reverse osmosis desalination membranes with minimal impact on performance in terms of the salt rejection or water permeation rate. An in situ grafting method has been developed to adapt the coated membranes for long-term operations.
1. Yang, R.; Gleason, K. K. Langmuir 2012, 28, 12266-12274.
2. Jiang, S.; Cao, Z. Adv. Mat. 2010, 22, 920-932.
3. Azzaroni, O.; Brown, A. A.; Huck, W. T. S. Angew. Chem. Int. Ed. 2006, 45, 1770-1774.
4. Zhang, L.; Cao, Z.; Bai, T.; Carr, L.; Ella-Menye, J.-R.; Irvin, C.; Ratner, B. D.; Jiang, S. Nat. Biotechnol. 2013, 31, 553-556.
5. Yang, R.; Xu, J.; Ozaydin-Ince, G.; Wong, S. Y.; Gleason, K. K. Chem. Mater. 2011, 23, 1263-1272.
6. Petruczok, C. D.; Yang, R.; Gleason, K. K. Macromolecules 2013, 46, 1832-1840.
7. Yang, R.; Asatekin, A.; Gleason, K. K. Soft Matter 2012, 8, 31-43.

Ice/frost formation and its accumulation is a common natural phenomenon having many adverse economic effects and safety issues related to aircraft, wind turbine, power grids, marine vessels, telecommunication devices, roads and transportation systems, commercial and household refrigeration systems, etc. Due to the practical importance of ice formation, significant research effort has been devoted by several groups around the globe to develop surfaces that facilitate the removal of ice or retard its formation. Superhydrophobic self-cleaning surfaces [1] due to their small contact area with water or ice, low heat transfer rate and self-cleaning properties, have been investigated extensively to address the problem of icing by passive means. Recently, superhydrophobic surfaces were also investigated for addressing the problem of frosting, which is even more challenging. Although superhydrophobic surfaces have been shown to delay the onset of frosting and icing, they cannot avoid it entirely. Hence effective deicing/defrosting via active means, such as heating, is required for many practical applications to keep surfaces free of ice or frost. In order to reduce response time and energy consumption, a new heating technique has been used to remove the ice and frost from the various surfaces with different wettabilities. Surfaces were synthesized by spray casting. Energy consumption of these surfaces in melting and shedding of sessile droplets was determined and compared for different tilt angles. The anti-icing performance of these surfaces under subfreezing surface temperatures and gently impacting supercooled (-10°C) sessile water droplets was evaluated. To better understand the defrosting process on polymeric textured nanocomposite surfaces, defrosting experiments were carried out on surfaces of different surface wettability, porosity and roughness. Strong influence of re-entrant morphology and surface porosity and micro roughness on condensation, condensation frosting and defrosting process was observed. Sustained ice- and frost-free operation was demonstrated at surface temperatures as low as -15°C in moderately humid ambient atmosphere (40%-45% RH and -10°C temperature).
References:
[1]. “Are Superhydrophobic Surfaces Best for Icephobicity?” Stefan Jung, Marko Dorrestijn, Dominik Raps, Arindam Das, Constantine M. Megaridis, Dimos Poulikakos. Langmuir 2011, 27, 3059-3066.

Despite years of advancement in making energy systems more efficient, the predominant mode of condensation seen in large-scale industrial processes is still filmwise condensation. Replacing the filmwise condensation mode with dropwise condensation promises large improvements in heat transfer that will lead to large cost savings in material, water consumption and decreased size of the systems. In this regards, use of superhydrophobic surfaces fabricated by texturing surfaces with nano/microstructures has been shown to lead decrease in contact line pinning of millimetric drops resulting in fast shedding. However, these useful properties are lost during condensation where droplets that nucleate within texture grow by virtue of condensation to large sized droplets while still adhering to the surface. Recently we have shown that liquid impregnated surfaces can overcome many limitations of conventional superhydrophobic surfaces during condensation. Here we discuss aspects related to condensation on liquid surfaces, and show how relations among surface tension of encapsulating liquid and condensing liquid determine the condensation and subsequent shedding behavior for condensing droplets. We compare the characteristics of condensed droplet behavior on these surfaces with their behavior on conventional un-impregnated superhydrophobic surfaces and show how use of lubricant impregnated surfaces may lead to large enhancement in heat transfer and energy efficiencies.

In this work, superamphiphobic (SAP) metallic aluminum alloy 2024 surfaces were produced with water and oil contact angles of more than 150° and sliding angle of less than 10°. The two simple and environmental friendly techniques of mechanical sanding and boiled water treatment were used to introduce micro- and nano-scale roughnesses, respectively, which resulted in a hierarchical morphology. Surface energy of the rough surfaces was reduced by coating them with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane agent. SAP property was absent for samples with micro- or nano-roughness only, and it emerged only after both kind of roughnesses were introduced. The highest contact angles approaching 158° for water, 156° for ethylene glycol and 154° for peanut oil were obtained after forming hierarchical structures involving shapes of micro-grooves obtained by one-directional sanding and nano-grass by immersing in boiled water for one minute. The effects of two approaches of random and one-directional sanding using various sandpaper grit sizes, and different time periods of treatment with boiled water on the wettability of surfaces were also investigated. In addition, fundamental wetting models were used in order to explain the experimental results obtained.

In this study we present a straightforward two step fabrication process of superhydrophobic PDMS silver nanorods arrays by using Glancing Angle Deposition (GLAD). First, the PDMS was mounted on custom designed stage to mechanically strain from 10% to 30% and then Ag nanorods were deposited at room temperature (RT). After deposition, the strain was released which induces the change in micro-scale roughness determined by ripples. The static contact angle of water droplet was measured. Along with increase in mechanical strain, the contact angle was observed to increase. The maximum contact angle of 151.8° ± 5.9° was observed for 30% stretched PDMS. Superhydrophobic surface was formed by subsequent release of the strain, which results into the buckling of silver nanorods grown PDMS surface. The dual-scale roughness and energetic barrier may be the responsible factors for wetting tuning.

In nature, many living things have functional surface according to their habitats. A number of researchers have studied these surfaces for many technical applications. One of these, Namib Desert beetle has unique back structure for collecting water in arid region. Their back is constructed hydrophilic bumps located in the hydrophobic domain. Vapor in the humid air is condensed in their hydrophilic bumps, and when sufficient water is condensed, drops are roll on the hydrophobic domain toward the beetle&’s mouthparts.
In this study, we have fabricated super-hydrophilic patterns on super-hydrophobic surface to mimic Namib Desert beetle. Above all, TiO2 nano-rods are grown on TiO2 coated Si substrate, and then the surface is treated using fluorine based self-assembled monolayer (SAM) to modify super-hydrophilic surface to super-hydrophobic surface. The SAM coated TiO2 nano-rods surface acts as background which droplets can fall down. After SAM coating, ZnO seeds is selectively deposited on TiO2 nano-rods using shadow mask and RF sputter for ZnO nano-rods growth. Using hydrothermal synthesis, ZnO nano-rods are grown on ZnO deposited spots. Finally, super-hydrophilic ZnO nano-rods on super-hydrophobic TiO2 nano-rods surfaces are completed to harvest the water. The surfaces have exposed the environments, which have proper humidity and temperature, for actual effect of the surface in the closed system.
As a result, we have fabricated the super-hydrophilic patterns on the super-hydrophobic surface using hydrothermal synthesis. We have analyzed the structure by Scanning Electron Microscopy(SEM), and condensation mechanism by Environmental Scanning Electron Microscopy(ESEM). Potential applications with this structure comprise microassembly, microfluidics, and lap-on-a-chip devices.

Characteristics of a material such as wettability, water-repellency, and adhesiveness greatly depend on the composition or structure of atoms and molecules of its surface. Therefore, a new function that differs from a base material can be given to its surface while making use of its original characteristics if the material surface is changed. In photochemical surface modification, VUV (vacuum ultraviolet) light is used as a means to modify the surface and develop new functions only on the part exposed corresponding to a mask pattern. This paper describes the method in which required functional groups (radicals) and atoms are incorporated on the surface of plastics selectively by using the photochemical characteristics of the VUV lights such as excimer laser and excimer lamp.
The principle of the photochemical surface modification of plastics is to detach dangling bonds from the chemical structure of the surface and incorporate desired functional groups in it. In order to perform the modification efficiently, following conditions must be satisfied: 1) the surface of a sample has a constituent (reaction compound) that has atoms to pull dangling bonds and desired functional groups (radicals) in its chemical structure, 2) the constituent has an absorption band in the wavelength of an excimer laser or lamp, and 3) the intermolecular bonding energy of the sample surface and the constituent is smaller than the photon energy of the laser or lamp.
Wettability is in general expressed with plasma irradiation, but it vanishes as the time passes after the treatment. Wettability also disappears when the treated surface is wiped. Its longevity is short. To make it longer, high power plasma was irradiated on the sample, but it caused micro cracks. Both the longevity of wettability and resolution incorporation have been improved when the surface was pretreated with weak plasma in a low VUV light irradiation in the presence of a reaction solution. After the plasma pretreatment, a reaction solution (thin layer of liquid containing radicals) was applied on the pretreated surface, on which a fused silica window was put, and VUV light irradiation was conducted when bringing the sample surface and the window in tight contact. By this technique, it became possible to incorporate functional groups only into the part exposed and to perform a lasting surface modification.
In this study, the contact angle with water of fluoroplastic (PTFE) untreated by plasma was 110 degrees, and it required 3000 shots with ArF laser fluence of 100 mJ/cm2 to form a copper film on the PTFE surface. With the pretreatment of plasma irradiation for 5 minutes, the water contact angle of PTFE decreased to 68 degree; whose wettability became high. As a result, a thin copper film circuit pattern was successfully formed with ArF laser fluence of 18 mJ/cm2, less than 1/5 of 100 mJ/cm2, and only 4 shots decreased drastically from 3000 in pulse.

Cerium oxide, belonging to the rare earth oxides (REO): has been studied widely because of its high hardness, excellent chemical and thermal stability and wear resistance, wide band gap and good adhesion to various substrates, etc. Because of these characteristics cerium oxide films have been used in solid oxide fuel cells, gas sensors and smart windows. A recent report suggests that the entire lanthanide series is intrinsically hydrophobic increasing the potential applications for these materials (Gisele Azimi).This new phenomenon has been attributed to the unfilled 4f inner orbital electron shell, which is shielded from interaction with the surrounding environment by the full octet of electrons in the 5s2p6 outer shell. In this talk, we will discuss the effect of oxygen pressure and substrate temperature during cerium oxide film deposition on the wetting properties of the oxide films. Cerium has two oxides, CeO2 and Ce2O3, which are grown by ablating a cerium target at various oxygen pressures. The thin films are deposited on silicon substrates using pulsed laser deposition. Transmission electron microscopy, x-ray photoelectron microscopy, atomic force microscopy and goniometer contact angle measurement are used for characterization. Our talk will discuss the effect of morphology and cerium valency on the wetting behavior and possible uses for these films in a variety of applications.
reference:
Hydrophobicity of Rare Earth Oxide Ceramics, Gisele Azimi, Rajeev Dhiman, Hyuk-Min Kwon, Adam T. Paxson and Kripa K. Varanasi, NATURE MATERIALS,vol12 ,Issue: 4, Pages: 315-320

Nanostructures (NSs) have been in focus of interest in the past few decades due to their unique electronic, magnetic, optical, and catalytic properties, which lead to novel applications. The ability to arrange NS into ordered 2D or 3D micro/nano structures is of utmost importance in developing new devices and applications of these nano-structures. Controlled spatial placement of nanostructures (NS) at micro/nano scale has attracted much attention due to their applications in NS based device fabrication. Different processes like, chemical interaction based to solvent driven patterned assembly of NS have been reported. Here we report patterned assembly of different NSs at micro/nano scale by controlling the surface wetting properties. Wet-able and non-wet-able patterned regions were created with patterns of self-assembled monolayer (SAM). SAMs with terminal end of -CH3 were used to create non-wet-able regions on gold/silicon surfaces. Micro-contact printing, e-beam lithography, and simple scratching techniques were used to create SAM patterns of different shapes. After dipping the SAM patterned surface in the NS solution or by putting a drop of NS solution on the patterned surface we observed NS assembly according to SAM molecular patterns in wet-able regions. We observed that wettability behavior of the surface plays a dominant role in NSs assembly in comparison to van der Walls and other interactions between surface and NS. Using similar process NS assembly on flexible substrate will be discussed.

Organic dye molecules in industrial wastewater pose special challenges as the molecules are relatively stable and resistant to many conventional abatement techniques. Weathering of organic dyes can produce toxic metabolites, conventional biological treatment processes are not effective, and adsorption and coagulation practices are expensive and causes secondary pollution.[1-3] The use of advanced photooxidation processes offer a more promising technological approach to the destruction of organic pollutants. In this process, sunlight and a semiconducting metal oxide catalyst combine to photooxidize dyes and other organic molecules to CO2.
Usually, the photocatalyst is used in the form of nanopowders or nanofilms.[3] Photocatalytic films, where catalyst particles are immobilized on a surface, offer advantages over dispersed particulates as they can be used directly, and in continuous systems, for purifying water under illumination. However, the main problem with the photocatalytic films is their reduced surface area and thus efficiency. In addition, a static boundary layer forms when fluids flow over the surface. Thus dye molecules would need to diffuse across this static boundary layer before they could come into contact with the catalytic surface. In this study we designed a superhydrophobic surface with catalytic particles partially embedded into the surface to reduce the static boundary layer while achieving good contact between the catalytic particles and the solution.
We used an inexpensive template lamination method to fabricate a TiO2-polyethylene nanocomposite surface that exhibits stable superhydrophobic properties without chemical surface modification of the TiO2 nanoparticles. Hierarchical roughness, spanning the micro to nano scale range, was formed onto the surface by using a template to emboss the polyethylene surface creating an array of polymeric posts while partially embedding TiO2 nanoparticles selectively into the top surface of these raised features. The TiO2 nanoparticles on the film surface absorb organic compounds from a droplet as it slips across the surface. The absorbed molecules are photoxidized under UV light and are replenished when the next droplet contacts the surface and the process repeats. The embossed region of the surface contains no TiO2 particles and so remains hydrophobic, contributing to the stability of the superhydrophobic properties. The ability of droplets to slip along the surface minimize the static solid-liquid boundary layer and we have demonstrated that this hierarchical surface significantly increases the degradation rates of dye molecules compared to static process.
1. Carp, O.; Huismanl, C. L.; Reller, A. Prog. Solid State Chem. 2004,32, 33-177
2. McCullagh, C.; Skillen, N.; Adams, M.; Robertson, P. K.J. J. Chem. Technol. Biotechnol. 2011, 86,1002-1017
3. Han, F.; Kambala, V. S. R.; Srinivasan, M.; Rajarathnam, D.; Naidu, R. Appl. Catal. A-Gen. 2009, 359, 25-40.

In this work the (anti-)icing properties of anodized aluminium with different surface chemistries are investigated. In order to obtain anti icing coatings use is made of the surface chemistry as well as the structure of the surface, which are often also related to the hydrophobicity of surface[1]. Recently it was shown that anodized alumina surface, which have a honeycomb like surface structure, can exhibit superhydrophobic properties[2]. In addition to the structural part of the coating also different surfaces chemistries are investigated; bare alumina, silanized and perfluorinated anodized alumina surfaces as well as liquid impregnated surfaces. Characterization is done in macroscopically as well as microscopically. Macroscopically the ice adhesive energy, the contact angle and contact angle hysteresis is experimentally measured. The ice adhesive energy is obtained by subjecting the iced samples to a guided impact test. On the Microscopic scale the properties of the surface are investigated using different methods of Atomic Force Microscopy. In order make fully use of the Atomic Force Microscopy imaging also the different surface chemistries on flat samples are examined. First the surface topography of the sample probed to obtain the surface roughness. Using Scanning Kelvin Probe Microscopy the surface potential of the different samples are mapped[3]. Combining these scales of measurement can enhance the understanding of these kinds of surfaces.
1. Farhadi, S., M. Farzaneh, and S. Kulinich, Anti-icing performance of superhydrophobic surfaces. Applied Surface Science, 2011. 257(14): p. 6264-6269.
2. Leese, H., et al., Wetting Behaviour of Hydrophilic and Hydrophobic Nanostructured Porous Anodic Alumina. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012.
3. Suzuki, S., et al., Hydrophobicity and freezing of a water droplet on fluoroalkylsilane coatings with different roughnesses. Langmuir, 2007. 23(17): p. 8674-8677.

Intercalation compounds containing clay minerals find a wide range of applications in composites, paints, drilling liquids, cosmetics, and medicine. This talk summarizes important chemical and physical properties of natural and organically modified clay minerals that help to understand the nanometer-scale structure, surface properties, and application in functional materials from a perspective of molecular simulation. We will discuss the cation density and surface polarity,[1] effects on the self-assembly of surfactants, surface forces, and responses of such intercalation compounds to temperature changes and photoexcitation.[2,3] The packing density, defined as the cross-sectional area of a surfactant chain in relation to the available surface area per cationic site, is a key quantity that affects tilt angles and interfacial dynamics.[4] Interlayer packing and mobility also depends on the chain length and the type of head group of attached surfactants and ionic adsorbates, which will be explained for several examples.[5,6] Thermodynamic models for the exfoliation of such layered compounds in composite materials, e.g., polymer matrices, will also be described, including specific contributions from cleavage energies of the intercalation compounds, the local creation of void spaces in the polymer matrix, and recombinant interfacial interactions.[6,7]
References
[1] H. Heinz Clay Miner. 47, 205-230 (2012).
[2] H. Heinz, H. J. Castelijns, U. W. Suter J. Am. Chem. Soc. 125, 9500-9510 (2003).
[3] H. Heinz, et al., Chem. Mater. 20, 6444-6456 (2008).
[4] H. Heinz, R. A. Vaia, B. L. Farmer Langmuir 24, 3727-3733 (2008).
[5] H. Heinz, et al., Chem. Mater. 19, 59-68 (2007).
[6] Y. T. Fu, et al., J. Phys. Chem. C 115, 22292-22300 (2011).
[7] Y. T. Fu, H. Heinz Chem. Mater. 22, 1595-1605 (2010).

Understanding boundary conditions at the liquid/solid (L/S) interface has been a subject of many scientific investigations and many debates. It also has important implications for design of materials for such applications as micro-/nanofluidics, where due to the large interface-to-volume ratio, functionalization of solid surfaces and the resulting L/S frictional slip are critical for the flow of the liquid. In addition, friction at the L/S interfaces influences flow of nanoparticles in liquids, which flow is utilized in a number of nanotechnology applications. Design of functionalized surfaces and interfaces with optimized friction and slip properties is hindered by existing challenges in measuring these properties either in experiments or in simulations. Here, we have developed a Green-Kubo (GK) relation that enables accurate calculations of friction at L/S interfaces directly from equilibrium molecular dynamics (EMD) simulations and that provides a pathway to bypass the time scale limitations of typical non-equilibrium molecular dynamics (NEMD) simulations. The GK relation is derived based on Generalized Langevin Equation (GLE) and the linear response theory. Details of the friction correlation function permit a full analysis of the time-dependent and frequency-dependent friction in a dynamic system. The theory has been validated for a number of different of interfaces and it is demonstrated that the L/S slip is an intrinsic property of an interface. Because of the high numerical efficiency of our method, it opens up new opportunities for computational design of functionalized surfaces for L/S applications.

We develop a theory to model the van der Waals interactions between liquid and graphene, including quantifying the wetting behavior of a graphene-coated surface. Molecular dynamics simulations and contact angle measurements were also carried out to test the theory. We show that graphene is only partially transparent to wetting, and that the predicted highest attainable contact angle of water on a graphene-coated surface is 96 degrees. One-atom-thick graphene is a “translucent” material for liquid wetting on a graphene-coated surface, with about 30% of the original van der Waals interactions between the liquid and the supporting substrate transmitted. Our findings reveal a more complex picture of wetting on graphene than what has been reported recently as either complete "wetting transparency" or complete "wetting opacity."

We report a unique tribological behavior of graphene when water droplet slides on it. We show that for graphene, there is no variation in the retention force for drop sliding as a function of the time the drop rests on the surface suggesting an instantaneous re-orientation process for graphene surfaces. We observe that the homogeneous and stable nature of graphene excludes the possibility of time changes in the intermolecular interactions between the liquid and the solid surface. Therefore, the only position for the three-phase contact line to pin on the surface is at the boundaries where graphene domains that nucleated at two adjacent nucleation sites meet. These boundaries form a complex micrometric tessellation whose shape is irrespective of the globally circular contact line, and hence should reduce its smooth nature. To simply put, contact line does follow the boundaries, but it is only its global circular form that has a shape irrespective of the boundaries. Indeed, we see that for graphene, the three-phase contact line forms a serrated micrometric structure, which differs from the smooth line on other surfaces. Using centrifugal adhesion balance (CAB) experimentally we show that the retention force of water drops on graphene surfaces does not depend on the drop resting time, in contrast to any other known systems. We further observe that the forces required to slide sessile and pendant drops on graphene sheets are similar.

Wetting phenomena are often associated with free surfaces. However, they are also relevant for impurity precipitation on buried, solid-solid interfaces in composite materials. We describe simulations of the precipitation of helium (He) on such solid-solid interfaces. The non-uniform precipitation of He at certain interfaces is a result of a heterogeneous energy distribution in the interface plane: He wets high interface energy (“heliophilic”) regions but does not wet low interface energy (“heliophobic”) ones. Using a phase-field model, we simulate the growth, coalescence, and stability of He networks on planar interfaces with patterned energy distributions. Our work leads to interface design criteria that predict whether stable linear pathways of He precipitates may form at a given interface. These criteria may be used in the design of structural materials with increased resistance to He damage, which is a major concern in nuclear energy applications.

Numerous experimental and theoretical investigations have been made to understand the behavior of water molecules under various conditions. Interfacial water behavior at semiconductor surfaces is one of the most important areas of investigation for diverse industrial applications such as crystal growth, lubrication, catalysis, electrochemistry and sensors. Although the terms, hydrophobic and/or hydrophilic, are often used to describe the macroscopic behavior of interfacial water based on contract (wetting) angle with surface, the effect of hydrophobicity on microscopic behavior of water is still not well understood and dynamics of interfacial water are still controversial. Computational study could provide a better understanding on the gap between macroscopic descriptor and atomistic behavior of water molecules at the interface. In this study, first principles molecular dynamics is employed to investigate the water behavior at silicon surfaces that are functionalized with several different molecules. Our study finds that similar adsorbates of non-polar characteristic can lead to significant change in dynamics of interfacial water molecules and their effects can be extended to nano-scale range. Physical origin of varying water dynamics associated with the adsorbates was elucidated from spatial distribution pattern of water molecules at the interface. Our study demonstrates how corrugation profile of the surface electrostatic potential plays an important role in determining interfacial water dynamics. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Robust hydrophobic materials can have broad applications in various industries including energy, water, and transportation [1-3]. Existing durable materials such as metals and ceramics are generally hydrophilic and require polymeric modifiers to render them hydrophobic [4], but these modifiers deteriorate in harsh environments. Therefore, robust hydrophobic surfaces have been difficult to realize and their widespread applicability has been limited. Here we demonstrate that all rare-earth oxide ceramics, ranging from ceria to lutetia, are intrinsically hydrophobic [5]. We attribute this behavior to their unique electronic structure that minimizes polar interactions with interfacial water molecules. To demonstrate their technological potential, we show dropwise condensation, water repellency, and sustained hydrophobicity after exposure to high temperature, steam, and abrasive wear. Since these ceramics are intrinsically hydrophobic, they can preserve their hydrophobicity even after damage at the surface. Hence, we envision that this class of robust hydrophobic materials will have far-reaching technological potential in various industrial applications.
References:
1. Quéré, D. Non-sticking drops. Rep. Prog. Phys. 68, 2495-2532 (2005).
2. Bocquet, L. & Lauga, E. Nature Mater. 10, 334-337 (2011).
3. Quéré, D. Wetting and roughness. Annu. Rev. Mater. Res. 38, 71-99 (2008).
4. Liu, K. & Jiang, L. Metallic surfaces with special wettability. Nanoscale 3, 825-838 (2011).
5. Azimi, G., Dhiman, R., Kwon, H., Paxson, A.T. & Varanasi, K.K. Nature Mater. 12, 315-320 (2013).

The evaporation of water from nanoscopic cavities is believed to play an important role in protein folding, the opening and closing of ion channels, and ligand binding to hydrophobic pockets. Path sampling and free energy calculation methods allow the determination of capillary drying rates, free energy barriers to drying, and the mechanism of association of hydrophobic solutes. Some implications for biological self-assembly processes emerge from these studies.
Hydration level modulates critical properties of proteins, such as their chemical and mechanical stability, biological activity and aggregation propensity. Understanding the recovery of native properties upon rehydration is essential to developing strategies for the repair and maintenance of biological substrates such as hair and skin, and for engineering long-term preservation methods for proteins. A molecular-based computational approach allows the calculation of thermodynamic, structural and mechanical properties of proteins during hydration and dehydration. The calculations provide insight into the various kinds of protein motion that occur as a function of water content.

Recently, we have demonstrated an artificial bio-electronic synapse based on specific recognition of the redox state of an electrochemically active self-assembled hydroquinone-alkanethiol monolayer (HQ) by an antibody selected from a phage display library to bind the quinone monolayer exclusively in its oxidized Benzoquinone (BQ) form. In a subsequent publication, the CDRs of the isolated antibody were embedded in a chimeric T-cell receptor expressed by an engineered T-cell line [Artzy-Schnirman et al., Nano Lett. 11, 4997 (2011)]. Presentation of the monolayer in its "off" HQ state left the cells inactivated but an application of a small oxidative bias to the monolayer switched it to the "on" BQ state, leading to specific T-cell receptor binding to the monolayer and consequently T-cell activation. This exquisite recognition of the state of an electrically active monolayer and the resulting electrically controlled activation of T-cells suggest a new class of bio-actuators based on real-time control over bio-recognition processes.
Sequencing of the antibody and its mutagenesis traced the binding to aromatic interactions between two phenylalanine residues in CDR3 of the heavy chain and the hydrophobic BQ rings of the monolayer in its oxidized form. Surface Plasmon Resonance (SPR) measurements suggested that the lack of antibody binding to the monolayer in its HQ state may originate from the blocking of the above interaction by water molecules that bind the HQ rings by a strong hydrogen bond to the proton added in the electro-reduction process. The switching of the electronic antigen between its "on" and "off" states was hence traced to an electrically controlled competition between antigen hydration and direct antigen-receptor binding. The generic nature of the suggested mechanism motivated a thorough study of the antigen monolayer physics.
Combining electrochemical, Quartz Crystal Microbalance, and electrochemical SPR measurements in mixtures of deuterated and normal water we found that each quinone ring binds and releases about one water molecule in a reduction/oxidation cycle. The kinetics and thermodynamics of the HQ/BQ layer has been studied as a function of monolayer density and hydrogen bonds strength, leading to a comprehensive understanding of the shielding of the artificial antigen-receptor interaction by water and the effect of hydrogen bonding with water and within the monolayer on the relative stability of the reduced and oxidized forms. Moreover, we found that although each molecule in the monolayer in either oxidized or reduced the monolayer as a whole displace more levels of hydrophobicity. Finally, our studies disclose unexpected relations between the electrochemical response of the monolayer and its hydration state. In addition to fundamental scientific questions, the discovered mechanism could open the way to a new class of bio-actuators.

Ferromagnetic shape memory alloys are an upcoming class of smart
materials with strong magneto-mechanical coupling, that have been attracting
increasing interest during the past years. Exhibiting magnetization changes
upon straining and, vice versa, reversible strains of several percent in response
to an external magnetic field, they are perfectly suited for biomedical
sensing or actuation. This particularly holds true as they can be operated
at constant (body) temperature at frequencies ranging from quasi-static to
some kHz. In contrast to the "prototype" Ni-Mn-Ga alloy, where the FSM effect
was initially discovered, Fe-Pd FSM alloys reveal excellent "basic" biocompatibility,
which makes them hot candidates for in-vitro and in-vivo use.
For use in cell and tissue actuators or strain sensors, sufficient adhesion to
mediate strains clearly constitutes a prerequisite. As the RGD sequence is the most
important binding motif for mammalian cells, which they express to facilitate adhesion,
the potential of RGD coatings to achieve this goal is explored. Employing large-scale
density functional theory calculations the physics of bonding between RGD and Fe-Pd
surfaces, which is characterized by coordinate bonds of O and N atoms to Fe, accompanied
by electrostatic contributions, is clarified. Theoretical predictions on adhesion, that
are confirmed experimentally, suggest RGD as suitable strain mediator to Fe-Pd surfaces.
On the cell side, favorable adhesion properties of RGD-coated Fe-Pd are manifested in cell
morphology and spreading behavior. Demonstrating that the adhesion forces between RGD and
Fe-Pd exceed those exerted by cells to the RGD coating, as well as traction forces acting
onto integrin bonds, the findings pave the way for novel type of applications as cell and
tissue actuator or sensor within the areas of tissue engineering and regenerative medicine.
[1] Y. Ma, M. Zink and S.G. Mayr, Appl. Phys. Lett. 96, 213703 (2010)
[2] M. Zink, F. Szillat, U. Allenstein and S.G. Mayr, Adv. Funct. Mat. 23 (2013), 1383

There is an acute need for the development of new energy-efficient solutions to separate oil-water mixtures. Mixtures of oil and water are classified based on the size of oil droplets (doil) - free oil if doil > 150 mu;m, dispersed oil if 20 mu;m < doil < 150 mu;m and emulsified oil if doil < 20 mu;m. In this work, we discuss a novel solution for the separation of free oil, dispersed oil, and oil-water emulsions based on hygro-responsive (from the Greek word ‘hygra&’ meaning liquid) surfaces. These surfaces, counter-intuitively, are wet by water, but are still able to repel low surface tension oils like hexadecane. This makes these porous surfaces ideal for gravity-based separation of oil and water as they allow the higher density liquid (water) to flow through while retaining the lower density liquid (oil). We will also discuss strategies that allow us to use these membranes for the continuous separation of surfactant stabilized oil-in-water and water-in-oil emulsions.

Oil/water mixture separation is a well-known challenge in environmental and industrial applications. One approach to this problem involves designing materials and surfaces that are both superhydrophobic and superoleophilic, and therefore can selectively absorb oil from the oil/water mixture. Inspired by the properties of the leaves of the floating water fern Salvinia [1], we introduce a surface with high aspect ratio fur-like nanohairs fabricated by hot pulling for use in oil/water mixture separations. Hot pulling is a highly scalable low-cost technique in which a softened polymer is locally elongated during demolding from a heated sandblasted steel plate, resulting in a dense nanofur. As a result of hot pulling, the wettability of polycarbonate changes from hydrophilic to superhydrophobic with contact angles up to 174 degrees. The measured oil uptake of the superhydrophobic and superoleophilic nanofur surface is up to 150 mL/m^2. Moreover, by combining hot punching and hot pulling techniques, porous structures with nanofur covered surfaces are created. The openings increase the oil absorption capacity of the nanofur, as well as allow the oil to permeate through for continuous filtration.
[1] Ribeiro, Rubio, Smith. Spill Science & Technology Bulletin 8, 483 (2003).

TThe presentation deals with the characterization of soot-templated superamphiphobic layers and new applications. For industrial use superamphiphobic layers need to be made in a simple, self-assembled process. This often leads to the use of aggregates of spheres. The optimal design of superamphiphobic layers fabricated from highly porous aggregates of nano- or micronot;spheres is discussed. This leads to criteria of how to optimize such layers for a particular applicanot;tion. The considerations are based on stability criteria valid in the static case. For highly dynamic liquids additional effects are important. Therefore we carried out drop impact experiments on superamphiphobic layers investigation the influence of interfacial tension and viscosity on the impact dynamics. As a novel application of superamphiphobic layers the solvent-free synthesis of polymeric microspheres is presented.

In recent years, growing environmental concerns have fueled the need for efficient oil and water separation systems. The danger of polluting natural waters, highlighted by the Deepwater Horizon spill, has spurred newfound interest in separation technologies. Aside from such disasters, fats, oils and greases are classified as hazardous waste and must be removed before discharging water to sewer systems or surface waters. In later stages of these oil recovery operations, up to 98% of the fluid extracted from reservoirs is contaminated water containing oils and other compounds that must be subsequently removed.
The scientific community has begun to respond to this problem by developing a variety of materials ranging from carbon nanotubes to aerogels to fluorosurfactant polymers that exhibit certain hydrophobic or oleophilic characteristics. Membranes offer cost-effective separation and in theory can completely separate two phase mixtures. To date, the hydrophobicity of membranes has been studied in great depth to improve the permeate flux. These membranes have been employed for the filtration of non-deformable components such as protein aggregates and macromolecules and function primarily on the principle of size exclusion. However, in the case of emulsified liquids, dispersed droplets can deform and squeeze through pores that are smaller than the emulsified droplet size, and pose a challenge to achieving high selectivity.
We report a membrane design that can separate emulsified droplets well below 1 µm in size. We consider the effects of both the geometry and the chemical properties of the membrane. The design displays potential for commercial viability due to its manufacturability and scalability for achieving high flow rates. We envision that this design methodology will extend beyond the separation of oil and water mixtures to realize separation of pharmaceutical emulsions, design of deployable separation devices, and control over phases in microfluidic devices. Additionally, we fabricate a novel asymmetric polymeric structure to improve the flow rates of a separation system while not comprising selectivity.

A wide range of emerging and conventional technologies rely upon the adhesive behavior of microparticles, including drug delivery, water/chemical purification, anti-fouling coatings, sensing, catalysis, composite processing, printing, and xerography. While microparticles possessing complex three-dimensional (3-D) shapes and rough surfaces are preferred for a number of these technologies, the ability to synthesize such particles: i) in a range of selectable 3-D morphologies, ii) in large quantities, iii) with well-controlled surface topographies, and iv) with tailorable chemistries for tunable adhesion remains a non-trivial challenge.
Nature provides a rich and sustainable source of complex-shaped, 3-D microparticles in the form of pollen. Various plants produce enormous quantities of pollen (e.g., over 1 million tons of ragweed pollen, Ambrosia artemisiifolia, are generated each year in the U.S. alone) with well-controlled (species-specific) 3-D shapes and surface topographies (e.g., smooth, reticulate, echinate, etc.). Recent work has shown that the van der Waals (VDW) based adhesion of pollen grains to various organic and inorganic surfaces scales directly with the contact radii of asperities present on pollen grain surfaces. Hence, appropriate selection of pollen species with known surface topographies may be used to affect such VDW-based adhesion.
We demonstrate here how 3-D ceramic microparticles with tailorable multimodal adhesion may be produced via the shape-preserving chemical transformation of pollen grains. While chemical modification of pollen particles has previously been studied for catalysis, water purification, drug delivery, or hydrogen storage, this is (to our knowledge) the first report demonstrating the syntheses of pollen-shaped ceramic microparticles with tailorable bio-enabled and synthetic modes of adhesion. A highly-conformal, computer-automated, layer-by-layer (LbL) surface sol-gel (SSG) deposition process and post-deposition firing have been used to convert pollen grains into magnetic, all-oxide replicas. By repeated cycling between exposure to an iron alkoxide-bearing solution, and to water, a Fe-O-bearing coating of controlled thickness was applied to dispersed pollen particles. Subsequent pyrolysis of the underlying pollen template and crystallization of the coating, under appropriate oxygen partial pressure and thermal conditions, yielded pollen-shaped, nanocrystalline ferromagnetic (hematite, α-Fe₂O₃) or ferrimagnetic (magnetite, Fe₃O₄) microparticles. High fidelity replication of the surface structural features (such as sharp, high-aspect-ratio spines) and 3-D shapes of particular (selected) pollen species, coupled with control over the type and amount of magnetic oxide within such replicas, allowed for the scalable generation of ceramic microparticles with tunable adhesion via short-range (~10 nm) VDW and longer range (~1 mm) magnetic forces.

Surfaces that exhibit contact angles close to 180#9675; for both polar and non-polar solvents are rare. In the present work, we will discuss the fabrication of such "omniphobic" surfaces by photolithography [1]. We investigate their stability against a so called wetting transition during evaporation of millimetric water droplets by systematically varying the shape and surface roughness of the micropillars on the surface [1]. We will show that a smooth curvature of the top of the micropillars strongly delays the transition, while it completely disappears when the surface roughness is increased [2].

We compare these experimental findings with existing models that describe the Cassie-Baxter to Wenzel transition and conclude that new models are needed which include the hurdle of an energy barrier for the wetting transition. Our results reveal that by increasing the roughness of the micropillars we do not affect the apparent equilibrium contact angle of the droplets. The dynamic robustness of the surface is, however, dramatically enhanced by an increase of the surface roughness [2]. Furthermore, an application of these surfaces for colloidal deposition will be discussed [3].
[1] A. Susarrey-Arce, A. G. Marín, S. Schlautmann, L. Lefferts, J. G. E. Gardeniers and A. van Houselt, J. Micromech. Microeng. 23 025004 (2013)
[2] A. Susarrey-Arce, Á. G. Marín, H. Nairs, L. Lefferts, J.G.E. Gardeniers, D. Lohse and A. van Houselt, Soft Matter 8, 9765 (2012)
[3] Á. G. Marín, H. Gelderblom, A. Susarrey-Arce, A. van Houselt, L. Lefferts, J. G. E. Gardeniers, D. Lohse and J. H. Snoeijer, Proc. Natl. Acad. Sci. 109, 16455 (2012)

Many different structured surfaces with a wide range of surface chemistries and topographies have been investigated for controlling the wetting (or non wetting) properties of a fluid/solid interface. Experimental advances in nanofabrication have led to the ability to achieve unprecedented control over the micro- and nano-texture of a substrate and this can result in almost perfect ultrahydrophobicity. Very few structured surfaces to date, however, have been able to achieve super-oleophobicity; i.e. resistance to wetting by low interfacial tension liquids such as hydrocarbons. Fluorinated silsequioxanes are nanometer-scale caged molecules that can be heavily fluorinated and molecularly dispersed in a range of polymers to systematically control both the hydrophobicity and oleophobicity (oil-repellency) of polymer substrates. Microtextured re-entrant structures coated with FluoroPOSS are the most oleophobic surfaces produced to date, with alkane contact angles greater than 150 deg. and low wetting hysteresis. We have also developed single-step dip-coating and spray-coating processes for applying such coatings to a wide-range of substrates. Applications of these nanostructured coatings include fabrics with enhanced solvent/oil resistance, surfaces for reducing environmental fouling and frictional dissipation, efficient separation of oil/water dispersions, reduction of ice- and gas hydrate-adhesion as well as ‘fog-harvesting surfaces&’ that greatly enhance our ability to collect solar-desalinated water from wind-borne fog.

A lot of research effort has been dedicated to engineering surfaces for enhancing water condensation rates,[1] but little attention has been dedicated to the engineering of surfaces for enhancing condensation rates of industrially-relevant working fluids with lower interfacial tension. Industrial fluids such as refrigerants, carbon dioxide, and methane are used extensively in a number of industries and the development of passive means for increasing their condensation rates can have significant economic impact. Here we use a custom condensation rig [2] to visually investigate condensation dynamics of a variety of liquids with surface tension in the range of 12 to 30 mN/m on hydrophilic, hydrophobic, superhydrophobic, and omniphobic lubricant-impregnated surfaces [2,3]. We demonstrate that flat hydrophobic and liquid-impregnated surfaces can both promote dropwise condensation of the majority of these fluids. However, we also demonstrate that on the lubricant-impregnated surfaces droplet pinning increases during later condensation stages. We discuss physical mechanisms responsible for increased droplet pinning and potential solutions to this issue.
References:
1. Rykaczewski, et al., Langmuir, 2013.
2. Anand et al., ACS Nano, 2012.
3. Smith et al., Soft Matter, 2013.

Lubricant-infused porous solid substrates are gaining remarkable interest as a new class of omni-repellent non-fouling materials and surface coatings. We investigated the effect of the length scale and hierarchy of the surface topography of the underlying porous substrates on their ability to retain the lubricant under high shear conditions, which is important for maintaining non-wetting properties under application-relevant conditions. By comparing the lubricant loss, contact angle hysteresis and tilt angles for water and ethanol drops on flat, microscale, nanoscale, and hierarchically textured surfaces subjected to various spinning rates (from 100 to 10,000 rpm), we show that lubricant-infused porous surfaces with uniform nanoscale features provide the most shear-tolerant liquid-repellent behavior, unlike superhydrophobic surfaces, which require hierarchical roughness for improved performance. Based on these findings, we present generalized, low-cost, and scalable methods to manufacture uniform or regionally-patterned nanoporous coatings on arbitrary materials and complex shapes. After functionalization and lubrication, these coatings show robust, shear-tolerant omniphobic behavior, transparency, and non-fouling properties against highly contaminating media.

Recently, anisotropic wetting or spreading surfaces of water have been studied extensively with inspirations from nature such as water-strider legs, butterfly wings and rice leaf. It is well established that the anisotropic wetting properties can be controlled by modifying texture and chemical treatment of surfaces according to the Wenzel and Cassie-Baxter models. As compared to anisotropic wetting surfaces for water, controllable anisotropic oil sliding surfaces have been rarely reported. Despite significant findings from many research groups, simple omniphobic surfaces are not capable of inducing a directional oil sliding property even in the presence of high contact angle and low contact angle hysteresis. This is due to the fact that the surfaces consist of randomly distributed re-entrant texture or regular arrays of beads or pillars.
In particular, many application areas such as microfluidic channels, mobile market, oil transportation and semiconductor industry need directional oil slippery surfaces to transport or collect remaing oil efficiently and to prevent contamination from the oil. Therefore, there are increasing demands on the non-sticky anisotropic sliding surfaces against oils. In this respect, we present overhang micro line arrays inspired from microgrooves of rice leaf to merge two properties: “omniphobicty“ and “anisotropic wetting“.
For the fabrication, a UV-assisted micromolding process with a mixture of photoinitiator and acrylate functionalized prepolymer containing aluminum oxide nanoparticles (Al2O3) was used, which offers a geometry-controllable, cheap and low-expertise route to the generation of a superhydrophobic hierarchical structure. Three different cross-sectional shapes of the microgrooves were employed to investigate the entry effect: prism, rectangle, and overhang structures. It was found that the surfaces with overhang line arrays allowed for anisotropic oil sliding surfaces as judged by low CAs and sliding angles of mineral oil (γ= 28 mN/m) and conventional photoresist (AZ 1512).

Wettability is a fundamental property of a solid surface, whose control plays an important role in many different industrial sectors from the ceramic one to the aerospace, naval or maritime, to that of electronics devices, pipes lines and so on.
In last years, a lot of studies have focused on the possibility of mimicking the high ability easily found in nature to repel water or other non-polar fluids trying to replicate it on synthetic materials. This concept draws inspiration from the hierarchical structure presented by various living organisms (i.e Lotus leaf, gecko, etc) that rely on a combination of surface morphology and chemistry.
Synthetic, super-hydrophobic surfaces, with a dramatically improved repellence to water and great application potential, should present static contact angle with water higher than 150° in order to exhibit enhanced self-cleaning attitudes. However, current knowledge suggests that surfaces with low contact angle hysteresis - defined as the difference between the advancing and receding contact angle in dynamic sliding movements of a fluid drop - are required to solve or reduce ice or fouling adhesion in materials withstanding adverse environmental conditions. In addition, design techniques coupling static and dynamic super-hydrophobicity with repellence to oils (termed as “amphiphobic” behaviour) would be extremely relevant to extend the application fields of many products.
In this work, different typologies of materials - ceramics, metals, alloys - were processed in order to get special wettability of their surfaces by means of chemical and microstructural modifications at nano-scale: functional top layers, made up of thin, hybrid coatings and deposited by dip coating, provided materials with extreme repellence to water from the static and dynamic point of view. By this way, optically transparent, homogeneous, nanostructured organic/inorganic hybrid coatings, with a thickness in the 200-300 nm range, have been generated by sol-gel method (particle dimensions of about 30 nm), followed by thermal processing and introduction of low energy elements, such fluorine. Static contact angles with water as high as 178°±1° were obtained on ceramic tile, aluminium and alloys, the same materials presenting excellent dewetting phenomena, as certified by the contact angle hysteresis lower than 5°±1°.
A good repellence against low surface tension fluids (oils and lubricants) was also obtained, this representing a significant improvement beyond the current state-of-the-art concerning amphiphobic products. Thin coatings were tested in order to investigate their mechanical resistance and durability to wearing phenomena, their anti-frost performances and resistance to chemical attacks. Up today, these results encourage to think that a new class of materials can be planned, bringing great convenience for different kind of industrial applications.

Recently, many kinds of polymeric thin films have been prepared. Particularly, the polymer brushes attract attention to control surface properties. So far, polymer brushes with specific property such as low frictional, high elastic, and adhesive surface have been prepared.
On the other hand, our group has reported that the radical crossover reactions of alkoxyamine units are useful for reversible structural reorganization of polymeric structures. Due to the reactivity of alkoxyamine units under heating condition, alkoxyamine-containing polymers can be reorganized after structural determination.
Here, we report the preparation and radical crossover reactions of alkoxyamine-containing polymer brushes for reversible wettability control. These polymer brushes undergo reversible grafting reaction of alkoxyamine-terminated linear polymers. One can obtain “tailored” surface property from the parent polymer brush.
Polymer brushes containing alkoxyamine units were prepared by surface-initiated atom transfer radical polymerization, and characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. To investigate the reactivity of the copolymer brushes, we treated the copolymer brushes with alkoxyamine-terminated polymers. For example, when the copolymer brush was heated with alkoxyamine-terminated poly(2,3,4,5,6-pentafluorostyrene), the surface showed more hydrophobicity. On the other hand, when the copolymer brush was treated with poly(4-vinylpyridine), the brush surface showed more hydrophilicity after the quaternization. Reversible grafting and de-grafting reactions were also confirmed by XPS and contact angle measurements. The results indicated that the dynamic covalent polymer brushes including alkoxyamine units are useful for reversible surface property control.

Adhesion of Cu interconnect lines to glass substrate has received a high attention for the application of advanced TFT-LCD because of their weak adhesion strength. In this report, we investigated the effects of various adding metal elements to the Cu films (about 300nm thickness) on the adhesion strength to a glass substrate by using a peel test. It was found that among the present adding elements with less than 10 at%, Mn and Zn elements had shown much higher bonding strength to a slide glass substrate and also superior thermal stability without defect formation (hillock and whisker) after vacuum annealing (~(10)^(-4) Pa) to 673K. In the case of a dilute CuZn alloy films ( Zn content of 0.6 - 6 atomic %) deposited on a slide glass (containing ZnO), the adhesive strength increased with increase in Zn content in the as-deposited films. However, the adhesion results showed that the deposited films on a 1737 glass (containing no ZnO) substrate exhibited weaker adhesion than those on a slide glass substrate. The cross-sectional-TEM(XTEM), EDX and XPS measurements of Cu98Zn2 films revealed that in the case of a slide glass substrate, both a preferential Zn segregation and a CuO formation were observed at the interface, accompanied by Cu grain growth after annealing in a vacuum (~10^(-4) Pa) at 573K. On the contrast, in the case of a 1737 glass substrate, there is no observable Zn segregation at the films-glass interface though the interfacial CuO formation was observed after vacuum annealing at 573K. Thus, Zn atoms in a slide glass substrate most likely played a role to enhance the segregation of Zn atoms to the films-substrate interface, resulting in increase in the adhesion strength to the glass substrate. From these present adhesion studies of a dilute Cu-Zn alloy film, It was tentatively concluded that a chemical exchange interaction between Zn atoms in both the films and the glass substrate can be expected to promote Zn segregation to the films-glass interface.
Keyword: adhesion, dilute Cu alloy films, and glass substrate.

The mechanisms of attachment and detachment of a micron-sized particle to and from a substrate in an aqueous environment is a fundamental concept relevant to numerous natural phenomena and industrial processes. Here we report a dynamic-induced enhancement in adhesion interactions between colloidal particles and substrates in an aqueous solution. This effect was identified by studying the trends of various particles (SiO2, Al2O3, and Polystyrene) on various substrates (silicon wafer, polystyrene, fused silica). Multiple tests were conducted to determine the impact of several factors including loading speed, loading force, and Young&’s modulus. We were able to isolate the change in retraction velocity over four orders of magnitude as the cause of the dynamic effect using the colloid probe technique on an atomic force microscope (AFM). The presence of a dynamic effect became clear upon observation of 20-100% increase in adhesion force resulting from an increase in retraction velocity from 0.02 to 156 mu;m/s during particle and substrate interactions. A dynamic model was developed to predict the adhesion forces resulting from this dynamic effect, and these predictions correlate well with the experimental results. The influence of dynamic factors related to adhesion enhancement, such as hydrodynamic effect, particle inertia, surface charging, viscoelastic deformation, and crack propagation were discussed to understand the mechanisms of dynamic enhancement.

Polymer surfaces with different roughness and chemical heterogeneity were prepared by self-assembly of block co-polymers and by soft lithography replication techniques. Their structure, adhesion, and friction were investigated by atomic force microscopy (AFM) and their suitability as substrates in friction measurements with the Surface Forces Apparatus (SFA) technique was evaluated in preliminary experiments.

Janus particles (e.g., spheres and dimers) have been investigated extensively in recently years due to their great potential in diverse applications such as drug delivery,[1] biofuel refining,[2] sensors, and colloidal surfactants. Current techniques in preparing Janus particles typically include template-assisted surface modification, electrodynamic co-jetting, Pickering emulsions, polymerization, and copolymer assembly.[3] However, those methods often have very low throughputs or are hard to control the Janus properties precisely.
Here, we report a new method to produce large amount of Janus colloidal dimers by using the reversible additionminus;fragmentation chain-transfer polymerization (RAFT) agent to functionalize two lobes of the colloidal dimers independently. Due to the characteristics of RAFT strategy, a large variety of monomers can be further polymerized on the modified surfaces under mild conditions. In particular, we will make poly(N-Isopropylacrylamide)-polystyrene dimers with both geometric and interfacial anisotropies. The synthesized amphiphilic dimers will then be used as colloidal emulsifiers to encapsulate and deliver nano-catalysts (e.g., Pd nanoparticles) into oil phase for efficient extraction of heavy oils underground.
1. Kumar, A.; Park, B. J.; Tu, F.; Lee, D. Amphiphilic Janus Particles at Fluid Interfaces. Soft Matter 2013.
2. Faria, J.; Ruiz, M. P.; Resasco, D. E. Phase-Selective Catalysis in Emulsions Stabilized by Janus Silica-Nanoparticles. Advanced Synthesis & Catalysis 2010, 352, 2359-2364.
3. Loget, G.; Kuhn, A. Bulk Synthesis of Janus Objects and Asymmetric Patchy Particles. Journal of Materials Chemistry 2012, 22, 15457.

Surfaces that possess liquid repellent properties are subject to intense research efforts, particularly due to their impact on solid-liquid contacts in many areas of applications. Examples for the use of such surfaces range from the generation of liquid repellent construction and packaging materials to the use of non-wettable surfaces in the context of construction of aircrafts, automobiles, and marine vessels, and extend all the way to medical devices.
So far, two main parameters that control the wetting properties of a surface have been identified. One of them is the topology of the surfaces, i.e., the size, height, and density of micro-/nanoscale roughness features which decorate the surfaces. The other is the surface energy of the material in question.
A large number of (in some cases bioinspired) superhydrophobic surfaces have been created in recent years.[1] On such surfaces water droplets exhibit a high contact angle and easily roll-off, which is the result of a low contact angle hysteresis. However, such materials remain sensitive to the presence of low-surface tension liquids and/or non-polar compounds stemming from the ambient. It has been shown that a requirement for the design of superoleophobic surfaces is associated with the presence of re-entrant structures, as a critical additional parameter.[2] The local geometric angle of structural features contained in textures with undercut structural elements enables the formation of metastable solid-liquid-air composite wetting states. This allows them to display non-wetting properties even towards low-surface tension liquids that would normally easily spread on the corresponding smooth surfaces. A novel approach towards a facile generation of non-wetting polymeric materials is presented.
1. Celia, E.; Darmanin, T.; Taffin de Givenchy, E.; Amigoni, S.; Guittard, F. J. Colloid. Interface Sci. 2013, 402, 1-18.
2. a) Tuteja, A.; Choi, W.; Ma, M.; Mabry, J. M.; Mazzella, S. A.; Rutledge, G. C.; McKinley, G. H.; Cohen, R. E. Science 2007, 318, 1618-1622. b) Tuteja, A.; Choi, W.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E. PNAS 2008, 105, 18200-18205.

Despite of advances in developing superhydrophobic surfaces, the practical application of such surfaces is still a challenge. To achieve the commercialization of superhydrophobic surfaces, two main issues need to be resolved: robustness with durability in harsh conditions and high throughput on large area with low cost. In this work, continuous fabrication of hierarchical wrinkling surfaces with superhydrophobicity on large area with high speed roll-to-roll nanoimprinting techniques has been realized. Hierarchical wrinkling pattern was prepared by nanoimprinting and swelling induced wrinkling as master mold. Perfluoropolyether hybrid mold replicated from master mold was used as flexible mold for roll-to-roll imprinting on modified Norland Optical Adhesive on polyethylene terephthalate (PET) flexible substrate. The obtained hierarchical wrinkling patterns on PET exhibit feasible superhydrophobicity without any further surface modification. Water contact angle of such patterns is higher than 155° and the sliding angle is lower than 10°. The superhydrophobic surfaces present good durability and robustness in various conditions, such as organic solvent, acid and alkaline, and have good self-healing properties. This is the first successful attempt in scaling up superhydrophobic surfaces using roll-to-roll techniques and the excellent behaviors of such roll-to-roll fabricated patterns show great potential for practical commercialization.

Lead-free (Pb-free) nano-solders hold tremendous potential as a viable solution for replacing traditional tin/lead (Sn/Pb) solders and offer many other exceptional manufacturing advantages. However, the knowledge of many properties of Pb-free nanosolders including their wettability, oxidation/corrosion, and intermetallic compound (IMC) formation and phase evolution is still very limited. Using a two-segment copper-tin (Cu-Sn) nanowire as a model system, in which Sn acts as the solder element and Cu serves as a functional element, we study the melting and phase evolution of Pb-free nanosolders and examine the environment effects on its solderability. The Cu-Sn nanowires are synthesized by an electrodeposition method using nanoporous templates. The Cu-Sn nano joints (nano junctions) are heated under vacuum, oxygen and hydrogen atmospheres, respectively. For heating under vacuum condition, it is found that eta;-Cu₆Sn₅ is initially formed and followed by the formation of ε-Cu₃Sn. The ε-Cu₃Sn is formed either at the Cu rich area (the end of the Cu segment) or Sn rich zone (adjacent to the remaining pure Sn). The formation of Kirkendall voids in the Sn segment indicates that Sn has a faster diffusion rate than Cu under this condition. For the solders heated under oxygen atmosphere (10 mbar of oxygen pressure), SnO is observed at the end of the Sn segment, both the ε-Cu₃Sn and eta;-Cu₆Sn₅ IMCs are formed, however kirkendall voids are formed at the end of both Cu and Sn segments. For the solders being heated under hydrogen environment (86 mbar of hydrogen pressure), no ε-Cu₃Sn phase formation is observed and the kirkendall void formation occurs at both the Cu and Sn ends. The prohibition of ε-Cu₃Sn phase under hydrogen atmosphere may be beneficial to improve the reliability of the solder interconnection.

Solution-processed electronic materials for printed electronics frequently take the form of nano-colloidal dispersion of inorganic materials, e.g., conductors, semi-conductors, and insulators. In standard printing processes, evaporation of the solvent plays a critical role in the deposition of the dispersed nanoparticles. Variation of the evaporative flux over the gas-liquid interface of the deposited dispersion leads to nonuniformities in the final deposition. During evaporation, nanoparticulates from dispersion preferentially self-assemble on the interface. To date, there is no quantitative study of the effects of particles on the interface on the evaporative flux. Studies of evaporatively driven bulk motions of colloidal dispersions culminating in deposition have ignored the presence of particles on the interface. We provide experimental evidence that nanoparticles present at the interface attenuate evaporation relative to the pure solvent case. To avoid the effects of the complex interfacial shapes attending patterned deposition by printing, we regularize the interface by conducting evaporation experiments in circular-bore cylindrical glass crucibles. We control the contact angle of the air-liquid interface with the crucible wall using silane chemistry. Experiments were conducted by placing the crucible on a sensitive scale contained within a glovebox whose humidity and temperature were carefully controlled. The crucible was initially charged with water, and the silica particles were placed on the interface using a modified Langmuir-Blodgett technique. Evaporation rates were measured as a function of surface coverage, contact angle, and surface properties of the nanoparticles. Theoretical models of nanoparticle-mediated evaporation are also considered.

Liquid metals have a wide range of potential applications including microelectronics cooling, electrical interconnects, micro-syringes and -pumps, and stretchable antennas.1,2 Gallium-based alloys have been proposed as a non-toxic replacement for mercury for such applications. Understanding of the wetting properties of such alloys is critical, but has only been recently explored from macroscale perspective due to complexities arising from surface oxide formation.1,2 Here we describe a novel methodology for exploring nano/microscale wetting and dewetting dynamics of liquid metals. Specifically, we use single beam Helium Ion Microscope (HIM) and dual beam Focus Ion Beam/SEM (FIB/SEM) to explore the wetting properties of Galinstan alloy in high vacuum environment with nanoscale spatial resolution. The surface oxide layer is removed using ion beam milling and liquid metal drops are perturbed using a tungsten nanomanipulator. We demonstrate that this approach provides a new avenue for understanding nano-to-microscale interactions of liquid metals with variety of solid substrates.
References:
1. Liu, et al. J. MEMS, 2012.
2. Kim et al. ACS App. Mater. Inter., 2013.

Patterned metallic structures with high resolution and high electrical conductivities are indispensable components of many common electronic devices. They find widespread use in a number of applications, e. g. as current collecting grids in photovoltaic cells and driving lines in displays and touch panels. Although the requirements for resolution, line definition and topology vary per application, in many cases very narrow lines with high aspect ratios are desired. Inkjet printing of silver based conductive inks is one of a number of approaches, due to its high flexibility, speed and efficient use of materials. In addition, it is a non-contact technique, which allows to print also on very sensitive surfaces. Inkjet inks, however, need to have rather low viscosities and consequently, their solid load is limited to a maximum of about 50 wt%, which in the case of silver usually corresponds to volume fractions well below 10 vol%. In addition, some degree of spreading of the ink droplets on the substrate will occur after deposition. As a result, the maximum heights of inkjet printed metal lines are usually limited to well below 1 micron, unless multiple printing steps are applied. To a certain extent, the degree of spreading can be limited by matching the surface chemistry of the substrate with the polarity of the ink, but this increases the risk of uncontrolled breakup of the ink deposits into uncontinuous and therefore nonfunctional structures. Silver lines with high aspect ratios are therefore difficult to achieve with this technology.
In this contribution, we present our findings on a method which allows to circumvent the limits of low metal load and ink spreading, resulting in continuous well-defined inkjet printed silver lines with very small widths and high aspect ratios. The approach makes use of the sequential evaporation of solvents with different boiling points and volatilities from the ink formulation, thereby continuously changing its polarity from within to outside the wetting envelope of the substrate. Interestingly, no break-up of the lines is observed, which results in line widths down to 20 microns and heights of up to 8 microns, corresponding to aspect ratios unprecedented with common single layer inkjet techniques.

A series of cellulose-ethylenediaminetetraacetic acid (EDTA) conjugates were synthesized by the esterification of cellulose with ethylenediaminetetraacetic dianhydride (EDTAD). The new polymeric chelators provided potent antimicrobial activities against Staphylococcus aureus (S. aureus, Gram-positive bacteria) and Pseudomonas aeruginosa (P. aeruginosa, Gram-negative bacteria), and inhibited the adhesion and formation of bacterial biofilms. The biocompatibility of the new cellulose-EDTA conjugates was evaluated with mouse skin fibroblasts for up to 14 days. SEM observation and DNA content analysis suggested that the new polymeric chelators supported the attachment and spreading of fibroblast cells. Moreover, in mouse skin fibroblast-bacteria co-culture systems, the new cellulose-EDTA conjugates prevented bacterial biofilm formation and protected the mammalian cells from the bacterial cells for at least one day.

Micro-encapsulation is a versatile tool for realizing innovative materials. The use of microcapsules is common in a variety of applications, such as home & personal care, food & feed, construction, pharma and agriculture. The synthesis of capsules is complex, and the analysis of encapsulated systems can be challenging. We are going to present selected approaches to micro-encapsulation, and methods for their physical and chemical characterization.

We report a growth of multiscale, hetero-nanostructure ZnO-Cu₂O surface exhibits superhydrophobicity and unsticky droplet bouncing. Two steps a) anodic etching and b) solution bath deposition are employed to grow the hetero-nanostructures. XRD and FE-SEM are used for phase and morphology characterizations, respectively. Subsequently, the hetero-nanostructure surfaces are hydrophobized using OTS-SAM and Teflon AF. These surfaces are characterized for static contact angle (CA), advancing-receding CA (ARCA) and the droplet bouncing/sticking characteristics for impinging droplet. Remarkably, Teflon coated surface shows highest CA of about 173^O. The droplet bouncing on these surfaces are studied in light of reversible transition from Cassie-Baxter to Wenzel state. The underlying surface morphology provides multi-scaled hierarchical roughness along with low surface energy coating that mimic the Lotus effect. Furthermore Teflon coated surfaces shows droplet bouncing at low to high Weber number (We ~ 72) whereas bare surface (CA~ 150^O) exhibits a sticky droplet above We > 30. Finally self cleaning property is also demonstrated on this Teflon coated ZnO-Cu₂O hetero-nanostructured surface.

Unwanted liquid-surface interactions afflict many applications where omniphobicity is a desired characteristic. Inspired by the Nepenthes pitcher plant, Slippery Liquid Infused Porous Surfaces (SLIPS) allow for super-repellency of a wide range of liquids [1]. These coated surfaces overcome drawbacks associated with traditional superhydrophobic surfaces that rely on the Cassie-Baxter model to generate liquid repellency, such as the wetting of micro/nanostructures by low surface tension solvents, limited self-healing properties, and low-pressure tolerance. SLIPS rely on a porous structure that securely holds a fluorinated lubricant within the structure by capillary forces and matching surface chemistry. Thus, the lubricant acts as the slippery interface with which liquids contact. Wetting of the liquid will not occur so long as it is immiscible with the fluorinated lubricant. The elimination of pinning points associated with solid-liquid contact results in extremely low contact angle hysteresis and sliding angles - an indication of super-repellency.
Our system employs a robust, simple, and scalable method of creating the underlying porous structure necessary for lubricant infusion and retention. This method involves depositing a uniform coating of silica colloids on a substrate surface using layer-by-layer deposition [2]. Electrostatic forces hold alternating layers of positively charged polymer and negatively charged silica colloids on the substrate surface. In theory, an indefinite number of these polymer/colloid layers can be deposited. We investigate a minimum number of layers required to create the surface roughness necessary to support lubricant retention. After removing the polymer layers, the colloids are surface functionalized with a trichlorosilane. Fluorinated lubricant is added to the surface in order to create the final SLIPS coating. After four to five layers, the porosity is sufficient for complete lubricant wetting allowing for liquids to slide off the surface at remarkably low angles (i.e., <5°). Transparency of substrates is also maintained due to the colloidal size being much smaller than the wavelength of visible light. This coating can also be applied to arbitrarily shaped surfaces, metals, and polymers as long as the initial substrate can be activated and cleaned of organic residue. Furthermore, complex and highly viscous liquids such as crude oil, honey, and ketchup can be repelled. The simplicity of the coating method allows for easy automation, low cost, and scalability guaranteeing practical use in a wide range of applications.
[1] Wong, T. S., Kang, S. H., Tang, S. K. Y., Smythe, E. J., Hatton, B. D., Grinthal, A., and
Aizenberg, J. Nature 2011, 477, 443
[2] Decher, G. Science 1997, 277, 1232

In this work we consider the hydrodynamic drag reduction for a perfectly hydrophobic surface in contact with a flowing liquid. We first show that at small Reynolds numbers (Stokes flow) an exact analytical model for drag reduction can be constructed for a sphere completely encapsulated in a layer of a gas.¹ The model predicts an optimum thickness for the gas layer for maximum drag reduction resulting from a competition between increased lubrication of the external flow and increased effective cross-section for drag by the compound object (the solid together with its surface-retained layer of gas). We then show from numerical simulations of flow of water past a sphere encapsulated in air that the maximum drag reduction increases from 19% to 50% as the Reynolds number is increased to 100; this is due to suppression of flow separation resulting in a narrower wake.² We show that roughness elements can be introduced into the numerical simulations to model a less idealised case of a superhydrophobic surface. This results in less effective drag reduction, because the vortex regime is no longer fully suppressed, although separation is delayed compared to flow past a smooth surface. Finally, we describe an analytical model of the flow resistance through pipes and tubes using similar conditions to the Stokes flow past a gas-encapsulated sphere.³ The relevance of these results to superhydrophobic surfaces and Leidenfrost layers will be discussed.
We acknowledge funding from the UK EPSRC (EP/G058318/1 and EP/G069581/1). GM acknowledges discussions and assistance from Dr. M.R. Flynn.
¹ McHale, G., Flynn, M. R., Newton, M. I. (2011). Plastron induced drag reduction and increased slip on a superhydrophobic sphere. Soft Matter7, art. 10100.
² Gruncell, B. R. K., Sandham, N. D., McHale, G. (2012). Simulatons of laminar flow past a superhydrophobic sphere with drag reduction and separation delay, Physics of Fluids25, art 043601.
³ Busse, A., Sandham, N. D., McHale, G., Newton, M. I. (2013). Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface. Journal of Fluid Mechanics doi:10.1017/jfm.2013.284.

It is understood, since 1940s, how roughness enhances non-wetting properties of hydrophobic solids. Maintaining superhydrophobicity of rough surfaces has relied on the presence of air in roughness grooves. Keeping these surfaces dry (non-wetting) under water is challenging because the plastron layer of trapped air is found to deteriorate. This technological barrier limits the utility of these surfaces in applications like drag reduction, boiling, among others. Here we demonstrate how immersed surfaces can stay at least partially dry under water. It is seen that surfaces retain non-wetting properties if hundreds of nanometer scale or smaller textures are used on hydrophobic solids. The proposed mechanism is the stabilization of the vapor phase of the liquid and of trapped gases in roughness grooves. There is a critical roughness scale below which these mechanisms are effective. Theoretical predictions are found to be consistent with the viable roughness length scales observed in experiments as well as on “air-retaining” insect surfaces. This approach is passive and does not involve active generation of gas. The ability to maintain vapor or gas pockets is crucial, e.g., to develop of highly efficient boiling heat transfer surfaces that initiate boiling at very low superheats or to develop low drag surfaces. This work also potentially paves way to develop textured surfaces to control phase change.

Super-hydrophobic materials are fascinating, in particular because of the various new functions they can provide to solids. We plan to discuss two such functions: 1) the ability to trap air, and to transport it, such as exploited by Argyroneta Aquatica, the underwater spider; 2) the ultra-low friction towards water (or water solutions), which can be tuned by varying the solid temperature. We discuss in particular how effects observed in a Leidenfrost situation (such as self-propulsion on asymmetric solids) can be extended to lower temperatures, using a superhydrophobic coating.

A parametric experimental study is performed to determine the physics behind the effect of surface texturing on the three important aspects of pool boiling heat transfer namely nucleation heat flux, boiling heat transfer coefficient, and critical heat flux (CHF). Boiling samples with different micro/nano textured surfaces were fabricated using semiconductor microfabrication techniques and pool boiling experiments are carried out to determine the heat transfer characteristics of each of these surfaces. The objective is to determine the relevant parameters that dictate an enhancement in these characteristics. The results show a substantial increase in CHF in the case of micro-textured surfaces and more so for the surfaces that also incorporate nano-scale texturing, yielding a maximum heat flux of 210 W/cm2. More importantly, it is seen that just increasing the roughness of these surfaces does not yield an indefinite enhancement in the CHF and that the micro and nano-scale texturing play very different roles in this enhancement. We propose a physical model that explains this CHF enhancement in terms of the surface wetting characteristics and the flow mechanics of the liquid-vapor contact line. Experimental results will also be presented detailing a clear trend in the effect of surface texturing on nucleation heat flux and the boiling heat transfer coefficient.

Water is essential for all the creatures, driving many animals and plants to develop intriguing materials and strategies in achieving efficient water collection from air. Some natural examples, such as spider silk [1], cactus [2], and desert beetle [3], have amazing abilities to capture and transport water droplets from fog by designing surfaces with special wettability. Spider silks are capable of colleting tiny water droplets in a directional manner by combining gradients of Laplace pressure and surface energy on a periodic spindle-knot structure. Cactus utilizes its conical spines that are covered by gradient grooves and oriented barbs as a continuous fog-collecting system. Desert beetles efficiently collect fog on their back with patterned wettability. Taking lessons from these natural examples, a series of functional materials with unique wettability have been fabricated [4-9]. For example, fibers with periodic spindle-knot structure has been successfully reproduced and subtly designed under controlled condition. These fibers can control the moving direction of condensed water droplets [4] and hang these droplets stably [5], and have excellent water collection ability [6]. These results provide inspirations in designing interfacial materials with unique wettability, which have applications in many fields such as water collection, liquid transportation, and treatment of polluted water.
[1] Y. Zheng et al., Nature 463, 640 (2010).
[2] J. Ju et al. Nat. Commun. 3:1247 doi: 10.1038/ncomms2253 (2012).
[3] A. R. Parker, C. R. Lawrence, Nature 414, 33 (2001)
[4] H. Bai et al., Adv. Mater. 22, 5521 (2010).
[5] X. Tian et al., Adv. Mater. 23, 5486 (2011).
[6] H. Bai et al., Adv. Mater. 23, 3708 (2011).
[7] H. Bai et al., Adv. Mater. 24, 2786 (2012).
[8] X. Tian et al., Adv. Funct. Mater. 21, 1398 (2011).
[9] H. Bai et al., Small 7, 3429 (2011).

This work describes the influence of the size and distance of micro- and nanostructures on the wetting behavior of surfaces. To this surfaces were equipped with regular post arrays etched into silicon substrates. Both the sizes of the posts and the distance between them were systematically varied. The thus obtained surfaces were coated with monomolecular layers of a fluoropolymer to ensure hydrophobicity. We have systematically studied the influence of surface structure onto the wetting behavior of water drops deposited on top of the structures. Our results indicate that the wetting of nanostructured materials is radically different from that of microstructured surfaces from a fundamental point of view: as the size scale of the surface features is decreased from micro to nano, a transition between a regime where strong drop pinning due to kinetic barriers occurs and where drops do not roll of the surface, regardless how strongly the substrate is tilted, to a regime, where contact angle hysteresis is small and truly superhydrophobic properties are observed. The latter case results in the roll off of droplets even at extremely small tilting angles. When in such systems the surface energy is varied distinct wetting transitions between the superwetting and the Wenzel regime as well as between the Wenzel and a superhydrophobic regime are observed.
To switch the wetting properties by an external stimulus, we have coated a silicon surface consisting of high aspect ratio nanoscale needles (“black silicon”) with a polymer monolayer containing a fluorinated azobenzene moiety. The azobenzene moiety can be switched between the cis and the trans state through illumination with light of appropriate wavelengths. In the described system the surface energy of the polymer coating is adjusted to the energy value which separates the distinct wetting regimes of the nanorough surface. This coupling allows for large changes in the surface wetting behavior even when the surface energy upon illumination is only rather small. As a consequence the surface can be reversibly switched from a superhydrophobic state with roll off tilt angle < 2° to a completely sticky surface with no roll off at all or from a strong Wenzel-type wetting state to a superwetting surface

Preventing or delaying the condensation frosting is of significant importance in many aspects of our daily life. Despite many efforts and improvements recently done in the design of new anti-icing materials, no efficient solution was found and frost formation remains an opened problematic.
In this trend, we study the condensation frosting on soft polymeric surfaces. It is known that the tunable viscoelastic character of these surfaces plays an important role in the condensation process1. By using several soft polymeric surfaces and a “classical” hard surface as a reference, we demonstrate that, even if soft surfaces are able to much more delay ice formation compared to the recent results reported in the literature on solid surfaces, condensation frosting is still inevitable under #8222;extreme“ conditions. We demonstrate that the ice growth mechanism occurs from droplet-to-droplet by a well-defined process, and we point out the universal behavior of the dynamical evolution of the frost front propagation, whatever the experimental conditions and the surface used.
Ref.
1. M. Sokuler, G. K. Auernhammer, M. Roth, C. Liu, E. Bonacurrso and H.-J. Butt, Langmuir : the ACS journal of surfaces and colloids, 2010, 26, 1544-1547.

The impact of drops falling onto solid surfaces is largely governed by inertial effects caused by the rapid deceleration of the drop. Recent theoretical and experimental studies showed, however, that the viscous squeeze-out of thin air layers underneath the drops plays an important role, potentially even for splashing. We developed a high-speed dual wavelength interferometry technique that allows us to follow the evolution of the (sub)micrometer thin air layer between the drop and the solid surface on a microsecond time scale up to its collapse. Here, we discuss the evolution and collapse comparing both smooth surfaces as well as microstructured surfaces with lithographically fabricated topographic steps and ridges.

In the presence of an electric field, the surface of an isolated spherical drop can deform into two Taylor cones. Conical deformations can also occur when a charged drop approaches another droplet or a solid surface. In these cases, the shape of the cone depends on the electric field strength relative to capillary forces, as well as the initial geometry. Once the two surfaces make contact, coalescence or dynamic wetting can proceed. In this talk we explore the spreading dynamics of conical drops. Specifically, we numerically investigate the dynamics for relatively low viscosity fluids, such as water, where the inertial forces dominate viscous forces. We find a family of self-similar solution that depends on material and geometric parameters, and we compare our theoretical findings to experimental results.

Roll-to-roll (R2R) processing is the ultimate goal for the manufacturing of flexible, innovative thin film devices like organic light emitting diodes (OLED) and organic photo voltaics (OPV). Organic and printed electronics are aiming at the development of light-weight, flexible and low cost products. High speed R2R deposition of the active materials from solutions (“inks”) on flexible substrates meets these goals. The performance of such devices often depends strongly on the homogeneity and thickness of the active layers. The accuracy demand is as challenging as 2 - 5 % maximum variation in layers in the nm thickness range.
Slot die coating is a proven technology for achieving thin and homogeneous layers fulfilling the demands dictated by the wanted device performance. It also meets the needs of a cost-efficient production. Solution-based deposition of thin films for OPV by slot die coating has already been demonstrated [1, 2, 3, 4]. Unfortunately, this technology is limited regarding the patterning of the deposited materials for functional devices. However, patterning of the deposited layers is essential for multiple reasons such as avoiding contact between electrodes and avoiding side leakage of water vapour and oxygen in encapsulated devices.
Currently two methods for the patterning of slot-die coated layers are used: the in-situ patterning using stripe-coating and intermittent coating and the post-patterning by means of removal of material where it is not needed/wanted after the coating step by e.g. using laser ablation or re-dissolving. Both methods are restricted, amongst others in speed, accuracy and/or resolution and also pattern shape.
Another approach is the use of dynamic wetting/dewetting to achieve a self-organised patterning of the printed/coated ink. We do this by modifying the surface energy (SE) of the substrate into high and low SE patterns. This technology has already been demonstrated for thicker layers and water based inks [5]. We enhanced the already demonstrated technology [5] to make it compatible with organic coatings and the high homogeneity demands, as for OPV and OLED lighting panels as well as for other applications in the printed electronics field.
We will demonstrate R2R technologies for the deposition of such patterns by CVD and plasma printing under atmospheric conditions. The technology will be discussed both from the fundamental and the practical point of view, addressing the chemistry and processing of the surface energy patterns, the physical process of dewetting and the flow to the desired patterns and the implementation of the fundamental understandings to optimise layout and processability.
1 Y. Galagan et al., Chemical engineering and processing 50 (2011) 454-461
2 F. C. Krebs, Nanoscale 2 (2010) 873 - 886
3. L. Blankenburg et al., Solar Energy Materials & Solar Cells 93 (2009) 476 - 483
4.F. C. Krebs, Org Electr. 10 (2009) 761
5 C. L. Bower et al., AIChE J, 53 (2007) 1644-1657

Scaffold topography is an important parameter in cell culturing. We prepared three types of 316L stainless steel surface with different topography by a Fine Particle Peening (FPP) treatment using titania, glass and alumina shot particles and analyzed the cell proliferation and cell-scaffold interaction. FPP treated surface with titania and glass particles had micro asperities at low frequency. On the other hand, the alumina treated surface had micro asperities at high frequency. L929 fibroblasts were seeded on these specimens and then the number of cells was counted after 72 hours of culturing. The FPP treated surfaces showed good cell proliferation comparing to polished surface. This indicates that micro asperities formed on the surface encourage cell adhesion. Cell adhesion behavior was evaluated by a scanning electron microscope (SEM) and a fluorescence microscope. Dense filopodia were observed when cells cultured on the FPP treated surface. This means that FPP treatment enhances cell adhesion and proliferation. The number of cells observed on the FPP treated surface depended on the shape of asperities formed by FPP treatment; the highest cell counts were obtained on alumina treated surface. This is because cell migration was not inhibited by the shape of alumina treated surface asperities.

Remora fish are capable of fast, reversible and reliable adhesion to a wide variety of both natural and artificial marine hosts through a uniquely evolved dorsal pad. This adhesion is partially attributed to suction, which requires a robust seal between the pad interior and the ambient environment. Understanding the behavior of remora adhesion based on measurable surface parameters and material properties is a critical step when creating artificial, bio-inspired applications. In this work, structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry were developed to predict the behavior of the seal with respect to host/remora surface topology and tissue material properties.

Microalgae are widely regarded as sustainable feedstock for biofuel production. Microalgae-derived biofuels have not been commercialized yet because current technologies for microalgae dewatering add a huge cost to the final product, and present a major bottleneck. We consider microalgae dewatering problem can be understood in the context of colloidal stability, where inter-algal potential is tunable via surface engineering of novel coagulation agents. We report here a nanoparticle-pinched polymer brush design that combines two known colloidal destabilization agents (e.g., nanoparticle and polymer) into one system, and allows the use of an external field (e.g., magnetic force) to not only modulate inter-algae pair potentials, but also facilitate retrieval of the coagulation agents to be reused after algal oil extraction. Our preliminary data on the preparation of well-defined nanoparticle-pinched polymer brushes, their structure-dependent coagulation performance on both fresh water and marine microalgae species, and their re-suability for continuous cycles of microalgae farming and harvesting will be discussed.

Chemical coatings on medical catheters are either antimicrobial or antifouling in nature, they are rarely both. However, coatings that consist exclusively of one given type of material have major drawbacks. For example, catheters with antimicrobial polymer coating may encourage sedimentation of dead bacteria cells, and this may provide a foothold for surviving bacteria to flourish [1]. Moreover, catheters coated solely with antifouling polymer may in the long run fail to prevent the bacteria from fouling the modified catheter surface once the bacteria eventually overcome the surface chemistry [1-2]. In this study, we show that by developing polymers with both antibacterial and antifouling functions, we can produce a coated surface that prevents bacterial fouling for a long period of time.
A series of polymers consisting of a polycarbonate backbone and random cationic pendant groups were synthesized via metal-free organocatalytic ring-opening polymerization. MPEG of various molecular weights were incorporated into the polymer as the initiator, and the respective polymers were grafted covalently onto silicone surfaces under ambient conditions. The study showed that surface coated with polymer containing 10 kDa MPEG proved to be most effective against S. aureus, and resisted bacteria surface fouling for a duration of 2 weeks. Moreover, surface coated with polymer having 2.4 kDa MPEG prevented E. coli fouling most extensively among the series of polymers synthesized. The surfaces coated with this particular series of synthesized polymers were also able to resist protein fouling and platelet adhesion, and did not cause significant hemolysis. In conclusion, this series of MPEG incorporated cationic polymers hold great potential as both antifouling and antimicrobial coating against selective bacteria, and to reduce the prevalence of catheter-associated bloodstream infections.
References
(1) Banerjee, I.; Pangule, R. C.; Kane, R. S. Advanced Materials 2011, 23, 690-718.
(2) Chen, S.; Li, L.; Zhao, C.; Zheng, J. Polymer 2010, 51, 5283-5293.

Control over the wettability of solid surfaces through surface chemistry and microscopic structure is key to a wide range of technological applications from dirt repellent and self-cleaning surface coatings to microfluidic lab-on-a-chip devices.
In this study we report the development of UV-imprint materials and roll-to-roll (R2R) UV-imprint processes for the large area manufacturing of superhydrophobic surfaces as well as microfluidic structures for capillary-driven water flow in open micro channels on flexible polymer substrates.
We have set up a custom made R2R nanoimprint lithography (NIL) pilot machine which is able to convert 10 inch wide web with velocities up to 50 m/min and developed UV-curable resins for UV-imprint materials. The Young&’s modulus and surface energy of the cured resins can be both tuned independently over a wide range by the cross-linking density and surface active dopants. We have achieved Young&’s moduli between 100 MPa and 5 GPa and surface energies between 12 mN/m and 60 mN/m.
The UV-resins were designed to fulfill the requirements of R2R-UV-NIL applications. They provide good adhesion to PET-substrates, high curing speed and facilitate easy and clean demolding from roller stamps or shims made of e.g. nickel, quartz or glass.
Furthermore, due to their capability for auto-replication the highly cross-linked and low surface energy UV-resins can be used for the manufacturing of polymeric working shims. The latter have the potential to replace the expensive and delicate nickel-shims in many R2R-NIL-processes.
While usually a hierarchical combination of micro- and nanostructures is regarded as mandatory for creating superhydrophobicity we have manufactured large area superhydrophobic surfaces with water contact angles asymp; 170° and roll off angles < 3° by R2R-UV-imprinting of simple micron-scale triangular ridge structures into very low surface energy UV-resins.
On the other hand we have found that water is wicking readily and fast in micron-scaled V-shaped grooves R2R-imprinted into hydrophilic UV-resins while the flat top surface stays dry. This directed and rapid capillary driven water flow within open micro channels is of particular interest for microfluidic applications like lab-on-a-foil devices.

The growth of semiconductor nanowires using the vapor-liquid-solid (VLS) mechanism requires the presence of a (self-) catalyst particle at the growth site, the diameter of which largely determines the wire diameter and the suitable growth conditions. In order to achieve the ordered growth of nanowires, regular arrays of equally sized catalyst nanoparticles are necessary. Gold is frequently used as a catalyst material for the growth of ZnO, Si and other semiconductor nanowires since it exhibits low euthectic temperatures with nanowire constituents like Zn and Si, respectively. Large-area arrays of gold nanodots can be easily fabricated on planar surfaces using nanosphere lithography (NSL) and physical vapor deposition. However, during the use in VLS nanowire growth processes, the catalyst particles dewet from the surface, form a liquid euthectic and in this state tend to coalesce with neighbouring catalyst droplets, which results in a delocalized growth of nanowires with non-controlled geometries.
In order to localize the position of Au nanoparticles on the surface in the solid and liquid state we created periodic anti-dot structures on the surface of 3C-SiC films on silicon. To this end, NSL nanomasks consisting of 600 nm diameter polystyrene beads were plasma modified and used to create Ni hard masks. Reactive ion etching was applied to transfer the mask pattern into the SiC film, resulting in a hexagonally close packed array of cylindrical nano-troughs with a depth of about 300 nm. Thin films of 30 nm Au were thermally evaporated onto the nanostructured SiC surfaces. It is shown that a lift-off process using HNO3 can be applied to remove Au from the SiC top surface completely while leaving the deposited gold inside the SiC surface troughs. Thus a hexagonally close packed structure of cylindrical nanotroughs containing Au is formed at the SiC surface. In this study the dewetting behavior of Au confined by the nanostructure morphology of the SiC surface upon thermal treatment and at conditions suitable for the catalyst mediated growth of ZnO nanowires in a temperature gradient furnace are studied by scanning electron microscopy, energy dispersive X-ay analysis, room temperature photoluminescence and transmission electron microscopy. In addition, the ion beam induced dewetting of Au films on nanopatterned SiC surfaces upon bombardment with low energy ions is investigated. In both cases, a strong impact of the surface morphology on the dewetting induced redistribution of Au on the inert SiC surface is observed.

Polymer substrates with a built-in capability for alignment of nanometer-sized objects are of interest for the development, performance, and large-scale production of robust, flexible devices. We have used atomic force microscopy (AFM) in friction mode to investigate the effects of uniaxial stretching on the chain orientation and nanoscale adhesion and friction of glassy polymer substrates. Examples will be shown of the different friction responses of semi-crystalline and amorphous polymers along and across the stretching direction, and how this friction response is altered as the strength of adhesion between the polymer and the AFM tip is deliberately changed.

A fundamental understanding of the effect of morphology and surface chemistry on the adhesion of polymers on metal oxide surfaces is crucial for the design of biomaterials and nanocomposites. Moreover, polymer - metal oxide interfaces play an increasingly important role for the design of adhesive joints relevant for lightweight construction.
In the first part of this study, zinc oxide nanorod films were prepared with different morphologies by controlling the film deposition time and by the addition of growth promoters. The adhesion of model epoxy amine polymers on these nanostructured zinc oxide surfaces was studied with and without polyacrylic acid interlayers. In the second part, the effect of the metal oxide surface chemistry was studied by application of acidic and alkaline pretreatments to adjust the surface hydroxyl density. The morphology and surface chemistry of the zinc oxide films was analyzed by means of Field Emission Scanning Electron Microscopy (FE-SEM) and X-Ray Photoelectron Spectroscopy (XPS), respectively. The stability of the polymer - zinc oxide interface under exposure to humid atmospheres was investigated by means of Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) Spectroscopy and 90° peel tests.
Our results demonstrate the positive effect of the increase in the surface area on the adhesion of the model epoxy amine polymer on the nanostructured zinc oxide surface [1]. This effect became more pronounced with the polyacrylic acid interlayer, possibly due to the lower molecular weight and thus the higher mobility of the polyacrylic acid chains enabling an improved diffusion into the voids of the zinc oxde nanorod film. Moreover, the results indicate that the acidic pre-treatment resulted in a decrease in the surface hydroxyl coverage, which led to an increased interfacial stability.
[1] O. Ozcan, K. Pohl, B. Ozkaya,and G. Grundmeier, Journal of Adhesion, (2013) 89-2, 128-139.

We report thin layer of polydimethylsiloxane (PDMS) in the thickness range of
64 to 77 nm can be generated multiple times (> 10) by utilizing irreversible bonding with oxygen plasma treatment and controlled interfacial fracture.
Silanol groups introduced by oxygen plasma treatment lead to irreversible
seal by dehydration through the chemical reaction. The modified PDMS surface has very different physical properties than those of the pristine PDMS, the large thermal mismatch by heating process can give rise to a cohesion failure during the peeling off. From auger electron spectroscopy result and contact angle measurement,
we show elemental constituent of transferred membrane (C, O, Si: 40%, 30%, 30%) and its hydrophobic property (~110°).

We could adjust the transferred height by controlling plasma treatment condition and curing density of PDMS stamp. When PDMS has low crosslinking density (low curing agent ratio or short curing time), because the penetration depth of plasma increases the height of transferred patterns become higher. Through simple scaling analysis based on the mechnism of wrinkling intability of a compressed platinum/PDMS bilayer, we confirmed that the modulus change of the PDMS and the trend of pattern height were exactly matched with the modulus change of the PDMS.
This simple method can be used to transfer micro and nanopatterns without a residual layer as well as to form nanochannels to several substrates.

Metal-polymer interfaces have attracted interest due to the increasing need of polymers as insulating materials in electrical and electronic devices, such as capacitors, cables and electronic circuits. Among the various polymers currently used, polyethylene (PE) is a very common insulting material due to its chemical stability and low cost. Thus, the PE-metal system is chosen as a model in this work. Strong adhesion at the metal-PE interface is required to prevent electrical and mechanical failures of the insulator system. For instance, the electronic structure variation across the metal-PE interface, which is a strong function of the adhesion at this interface, determines charge carrier injection and dynamics. In this work, density functional theory (DFT) was used to study a variety of metal-PE interfaces in order to (1) determine the mechanical strength of the interface, and (2) identify the correlations between interfacial mechanical strength and interfacial electronic structure.
The metal-PE system was studied by considering different metals, including Al, Pt, Ag and Au. Several orientations of the metal as well as PE were considered, including the (100), (010) and (001) surfaces. As van der Waals (vdW) interactions dominate the structure of polymers, and their interaction with metals, such interactions were included by the use of Tkatchenko-Scheffler (TS) functional. The interfacial work of separation, the effective work function of the metal, and the barrier heights for electron and hole injection were computed. Based on these results, a comprehensive understanding of the mechanical-electronic property correlations was obtained, which will allow for the identification of design guidelines to improve both the mechanical strength and electronic structure of metal-polymer interfaces.