Gels - polymeric networks swollen with a substantial amount of solvent - represent a fascinating class of soft materials, with wide-ranging applications in fields as diverse as biomedicine, pharmaceutics, personal care products, foods, sensors, actuators, flexible electronics, oil recovery, and adhesives. Physical gels are held together by non-covalent interactions, which may be as specific as hydrogen bonds, or as general as solvophobic association of insoluble blocks. Among the attractive features of physical gels are reversibility, stimuli-responsiveness, and tunability of macroscopic properties. There are exciting opportunities to design new gel systems based on block copolymers, given the relative ease with which tailored architectures can be synthesized by modern controlled polymerization techniques. In this talk two classes of physical gels will be highlighted. In one, the ability of ABC block terpolymers to form novel gel structures in water will be demonstrated, where blocks A and C are mutually immiscible and hydrophobic, while B is hydrophilic. In particular, the formation of hydrogels by sequential association (first A, then C) leads to a remarkably sharp gelation transition, at a relatively low polymer concentration. In the second system, gels formed by hydrogen bonding between the endblocks of a fully soluble ABA triblock and a separate, C homopolymer “crosslinker”, will be described. In this case the solvating medium is an ionic liquid, which affords access to a wide range of temperature and unprecedented rheological response.

Polymeric vesicles, or polymersomes, are of great interest in the nanomedicine community owing to their ability to transport both hydrophobic and hydrophilic substances and their controllable membrane properties. Our research group has recently shown that nanoparticles affect the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, with the addition of hydrophobic iron oxide nanoparticles, micelle-forming block-copolymers produce polymersomes (magneto-polymersomes) instead of micelles (magneto-micelles). In addition, we find that the sizes of polymersomes are controlled by varying the size of incorporated nanoparticles. This size-controlled self-assembly of magneto-polymersomes was attributed to the membrane curvature change caused by the localization of nanoparticles in the inner layer of polymersomes. Finally, we show that while the magneto-polymersome size decreases with nanoparticle size, the transverse relaxivity rates (R2) increase. Specifically, a R2 value of 555 ± 24 s-1mM-1 was found for polymersomes with a size of 241 ± 16 nm, which is the highest value reported to date for polymeric structures with iron oxide nanoparticles.

We report a new microfluidic emulsification technique for production of water-in-oil-in-water (W/O/W) double-emulsion drops with an ultra-thin middle layer as templates for microcapsules. When two immiscible fluids flow through a single capillary channel, one fluid with lower affinity to the wall flows through the center of the channel without contacting the wall, while the other fluid flows along the wall. Such core-sheath flows can be emulsified into the third fluid in a capillary microfluidic device, leading to formation of double-emulsion drops consisting of a large core and an ultra-thin shell; the ultra-thin shell provides high degree of confinement of the core drops due to strong lubrication resistance along whole surface, making the double-emulsion drops highly stable. Therefore, by employing the double-emulsion drops with ultra-thin shell as templates, we can safely encapsulate any water-soluble materials into microcapsules with ultrathin membrane, without rupture of the templates, through solidification of middle phase. The solidification can be achieved by evaporation-induced consolidation of organic middle phase containing polymers; the membrane can be biocompatible and biodegradable by using polymers such as poly(lactic acid) or polycaprolactone. Therefore, we can achieve a long-term release of encapsulants from the capsules as the membrane slowly degrades by hydrolysis. In addition, doping of magnetic nanoparticles into the membrane renders the capsules magneto-responsive; this enables migration or concentration of the capsules upon application of external magnetic field. Moreover, the surface morphology of the membrane can be further tailored by using polymeric blends; selective removal of one polymer from the blends produces perforated membranes, providing selective permeability of encapsulants. Using modified designs of capillary microfluidic devices, multiple distinct materials can be separately encapsulated into the microcapsules with multiple compartments. For example, through parallelization of the core-sheath streams, two or more distinct innermost drops are covered by nonspherical envelop of middle layers; such drops can produce microcapsules with dumbbell or triangle structures. Therefore, the capsules can store and release multiple materials simultaneously, while avoiding their cross-contaminations. In addition, capsules-in-capsules structure can also encapsulate multiple materials; such hierarchical capsules can be prepared by quadruple-emulsion drops in elaborate microfluidic devices. Because rate of membrane degradation can be independently controlled for inner and outer membranes, the capsules-in-capsules structures enable controlled sequential release of multiple encapsulants in a programmed fashion. Such various functional microcapsules with ultra-thin membranes will provide new opportunity for practical biological delivery systems and microreactors.

Introduction The kinetic control of solvent processing and ageing time combined with acid-base complexation offers great flexibility for the creation of new morphologies in solution and outstanding ability to control and manipulate those morphologies. When acidic blocks are present, assembled structures are tunable in a well-defined way via co-assembly of organic bases with adjustable chain structure and also with control of the solution assembly pathway. A rich variety of polymeric nanostructures have been made such as toroids, disks, and helical cylinders from poly(acrylic acid)-containing diblock and triblock copolymers in THF/water mixtures with multiamines to complex with the PAA. Both the type and amount of multiamine were found to be critical for formation of specific micelles. Due to low chain exchange dynamics between block copolymeric micelles in water-rich solution, global thermodynamic equilibrium is extremely difficult, if not impossible, to achieve. In our block copolymer/THF/water/multiamine quaternary systems, thermodynamics and kinetics of morphological evolution are governed by three important factors, including chain length of hydrophobic blocks, ratio of THF to water, and the interaction of multiamine with hydrophilic PAA block in the corona. By taking advantage of slow kinetics behavior of polymeric micelles in solution, one can purposely produce multicompartment micelles and mulitgeometry micelles by mixing different PAA-containing block copolymers together but forcing them to ultimately reside in the same nanoscale structure through kinetic processing. While kinetically trapped in common nanostructures, local phase separation can occur producing compartments. This compartmentalization can be used within common micelle geometries to make complex spheres and cylinders, spheres will specific intersphere interaction for sphere chain formation, or can be used to make new nanostructures such as multigeometry aggregates (e.g. hybrid cylinder-sphere aggregates).

Many opportunities are emerging to design self-assembling and functional supramolecular materials. The components can be small molecules, inorganic lattices of low dimensionality, or covalent polymers. Their functions can range from electronic properties relevant to energy to catalysis and bioactivity. The design of supramolecular materials involves programming of molecules to engage in specific interactions with each other and with external forces to generate highly functional structures. There remains a grand challenge in designing structures with various types of order at different length scales that are hierarchical as observed in biological systems. This lecture will describe one-dimensional self-assembly of small molecules into supramolecular polymers to generate electronic functions of interest in photovoltaics, and also bioactivity of interest in regenerative medicine. Other systems to be described go beyond one-dimensional assembly into networks that can exhibit ferroelectric or pleochroic behavior. A third family of supramolecular materials is described that form complex structures with covalent polymers to create photosynthetic functions.

Hybrid soft material/metallic nanoparticle (NP) systems are viable for wide range of applications, from biosensors to optoelectronics. One class of functional hard/soft hybrid nanocomposites is formed when ordered A-b-B diblock copolymers (BCPs) are exploited as scaffolds for the directed assembly of nanoparticles over large length-scales. Of specific interest in this presentation is the structural and temporal evolution of the topography of thin film BCP/NP systems. By way of context, the topography of a supported thin film A-b-B block copolymer (BCP) is composed of islands (or holes), provided the thickness of the film, H, meet certain selection criteria. Using a combination of optical microscopy, scanning transmission electron microscopy and atomic force microscopy, we investigated the effect of nanoparticles on the time-dependent evolution of the topography of hybrid BCP/NP thin films of thickness of H<2L on a substrate. The islands (holes) increased in size with a growth rate that exhibited a power law dependence, suggesting the dynamics are self-similar. More importantly, based on probability density distributions of the data, the classical coarsening mechanism, coalescence, was shown to dominate the growth of the islands of the pure BCP during the early stage, whereas Ostwald ripening, where the larger islands grow at the expense of the smaller ones, became the dominant mechanism at later times. In the hybrid system however, islands grew at a considerably smaller rate, primarily via coalescence. The coarsening of the islands is reminiscent of that of 2-dimensional phase ordering systems of binary alloys, magnetic systems and others

Amphiphilic block copolymer vesicles in aqueous medium, coined “polymersomes”, are highly promising drug delivery systems because they have both a hydrophobic membrane and a hydrophilic interior reservoir available.[1] A new challenge consists in complexifying these polymersome structures by forming multicompartmentalized polymersomes or polymersomes in a polymersome in order to roughly mimic the compartmentalized structure of a cell, the most complex and evolved entity in Nature. Moreover, the delivery of multiple functional components (like anticancer drug cocktails) or incompatible actives[4] in one single larger carrier would thus become possible. In another perspective, multiple polymer barriers should enable a better control of release properties and offer a better protection to the encapsulated actives[5]. This tuning of membrane properties would also open a path to future oral absorption deliveries, as each polymersome membrane could be designed for degradation in specific environments. So far, we have been able to encapsulate nanometric poly(trimethylene carbonate)-b-poly(L-glutamic acid) PTMC-b-PGA polymersomes formed by nanoprecipitation in giant poly(butadiene)-b-poly(ethylene oxide) PB-b-POE polymersomes thanks to the emulsion-centrifugation method[6]. This structure was assessed by laser confocal microscopy thanks to multiple fluorescent labelling; this also enabled us to demonstrate the multiple loading in compartments thus arising. The permeability tuning of such structures could be demonstrated by comparing the in vitro release of doxorubicin from loaded nanosize vesicles, when these were single or encapsulated in giant polymersomes.[7] In a later work,[8] the nanosize vesicles were dispersed in highly viscous alginate or dextran solutions, to mimic roughly the cytosol along with organelles, for the first time in vesicles. The 2D motion of these organelle mimics alone was tracked down in a movie and confirmed as still being Brownian inside a giant polymersome. Furthermore, by comparing this method with dynamic light scattering on the solution before its loading, we could assess the validity of our particle tracking analysis and confirm that the nanosize vesicles are not disturbed by their encapsulation. In the presence of “cytosol mimic dextran”, their motion was proved to be efficiently hindered as confirmed by a 6.6 times smaller diffusion coefficient! [1] a) C. Sanson, et al., Langmuir 2009; b) K. Kumar Upadhyay, et al., Biomacromol. 2009, 10, 2802-2808. [2] R. C. Hayward, et al., Langmuir 2006, 22, 4457-4461. [3] S. A. Walker, et al., Nature 1997, 387, 61-64. [4] H. C. Shum, et al., Angew. Chem. - Int. Ed. 2011, 50, 1648-1651. [5] B. Wong, et al., Adv. Mater. 2011, 23, 2320-2325. [6] E. Mabrouk, et al., PNAS. 2009, 106, 7294-7298. [7] M. Marguet, et al., Angew. Chem. - Int. Ed. 2012, 51, 1173-1176. [8] M. Marguet, et al., Langmuir 2012, 28, 2035-2043.

Filled microcapsules made from double emulsion templates in microfluidic devices are attractive delivery systems for a variety of applications. In the microfluidic approach, water/oil/water double emulsions are formed in two dripping events, after which the monomeric oil phase is consolidated by photopolymerization, forming a capsule with an aqueous core. This allows for facile tailoring of the microcapsules through a large number of variables, which in turn makes these systems more challenging to predict. To elucidate these dependencies, we start from theoretical predictions for the size of double emulsions, which are based on the ratio of shear and interfacial forces acting on the droplet surfaces. Combined with experimental data, we present quantitative design maps that correlate parameters such as fluid flow rates and device geometry with the size and shell thickness of monodisperse polymer-based capsules produced in microcapillary devices. Using polymers with selected glass transition temperatures as the shell material, we show through single capsule compression testing that hollow capsules can be prepared with tunable mechanical properties ranging from elastomeric to brittle. Weibull statistical analysis of the load at rupture of brittle capsules is also provided to evaluate the variability of the microfluidic route and assist the design of capsules in applications involving mechanically triggered release. The permeability of the capsules can also be tailored through the choice of polymer and addition of cross-linkers or plasticizers. Finally, we manipulate the microstructure of the capsule shell by adding silica nanoparticles to the middle phase of the double emulsion templates. With different silanization treatments or surfactants, we can vary the wetting properties of the particles and thus influence their location within the capsule shell. Good wetting leads to homogeneous composite shells, allowing for further variation of the mechanical properties. Medium or low wetting can result in layered structures, where the particles occupy only the outer and inner surfaces of the shell, allowing for subsequent surface modification of the entire capsule.

Amphiphilic Janus particles are composed of both hydrophilic and hydrophobic regions. The synthesis and applications of amphiphilic Janus particles, including stabilization of emulsions, were studied for the past several years. Previously, we have developed electrohydrodynamic (EHD) co-jetting to fabricate multicompartmental anisotropic particles with different functionality in each compartment. Here, we report a new strategy to produce amphiphilic Janus particles via EHD co-jetting. In this technique, selective encapsulation of hydrophobic fluorodecyl-polyhedral oligomeric silsesquioxane (F-POSS) in one hemisphere and selective hydrolysis of poly(vinyl acetate) (PVAc) in the other hemisphere results in amphiphilic Janus particles. We have investigated the behavior of the amphiphilic Janus particles at an oil-water interface. The surfactant-like amphiphilicity allows strong adsorption of these particles at the interface. The combination of such amphiphilicity and nanoscale particle size is an important prerequisite for particulate surfactants to effectively stabilize emulsions.

Nowadays, tuning the properties of next generation materials over a large range has become of great interest. In this respect, increasing the level of complexity is considered as a powerful tool, since it allows targeting numerous constitutive elements of these systems. This can be achieved by hierarchically assembling small building blocks, over two or more level of assembly [1]. To this aim, supramolecular chemistry has offered a straightforward approach, allowing the construction of highly complex and dynamic structures by means of non-covalent interactions [2]. In parallel, combining macromolecular and supramolecular chemistries has proven to be an unprecedented approach to responsive polymeric architectures with adaptable and self-restructuring properties [3]. Among them, polymer networks, where crosslinks were supplied by one or a combination of intermolecular interactions, received a particular attention, mostly because of their intrinsic self-healing ability [4]. In our studies [5], well-defined diblock copolymers end- or side-functionalized by terpyridine ligands are synthesized by controlled radical polymerization in the presence of either a functionalized initiator/transfer agent or monomers bearing the terpyridine moiety. These materials are then hierarchically organized over two levels of self-assembly to yield metallo-supramolecular micellar gels. The first level of self-assembly is achieved upon the dissolution of the diblock copolymer in selective solvents. The second level of self-assembly is triggered upon the addition of metal ions to the micellar solutions. Depending on the nature of the different constitutive elements, soft materials presenting quite distinct rheological properties are obtained. Further tuning over their rheological properties is possible over the two levels of assembly, e.g. by varying the morphology and softness of the micellar cores or by playing on the balance between intra-micellar loops and inter-micellar bridges. Finally, the incorporation of stimuli-responsive sequence opens up the possibility of imparting additional responsiveness to the hierarchically organized material. References 1. H. B. Yao, H. Y. Fang, X. H. Wang and S. H. Yu, Chem. Soc. Rev., 2011, 40, 3764; G. M. Whitesides and B. Grzybowski, Science, 2002, 295, 2418. 2. J. M. Lehn, Chem. Soc. Rev., 2007, 36, 151. 3. K. A. Williams, A. J. Boydston and C. W. Bielawski, Chem. Soc. Rev., 2007, 36, 729. 4. D. G. Kurth and M. Higuchi, Soft Matter, 2006, 2, 915; J. B. Beck and S. J. Rowan, J. Am. Chem. Soc., 2003, 125, 13922. 5. P. Guillet, C. Mugemana, F. J. Stadler, U. S. Schubert, C. A. Fustin, C. Bailly and J. F. Gohy, Soft Matter, 2009, 5, 3409; J. Brassinne, C. Mugemana, P. Guillet, O. Bertrand, D. Aulh, C. Bailly C.-A. Fustin, and J.-F. Gohy, Soft Matter, 2012, 8, 4499.

Copper-based ATRP (atom transfer radical polymerization) catalytic systems with polydentate nitrogen-based ligands is among most efficient controlled/living radical polymerization systems. Recently, by applying new initiating/catalytic systems, Cu level in ATRP was reduced to a few ppm. Various reducing agents, including metals, organometallic species, sugars, amines, phenols, monomers ligands, radical initiators or electrical current have been successfully applied. Similar control can be achieved with ppm of Fe-based catalysts. ATRP of acrylates, methacrylates, styrenes, acrylamides, acrylonitrile and many other vinyl monomers provides polymers with molecular weights in a large range 200

Cationic ruthenium-alkylidene complexes, e.g., [Ru(DMF)3(IMesH2)(=CH-2-(2-PrO)-C6H4)]2+(BF4-)2] (1, IMesH2=1,3-dimesitylimidazolin-2-ylidene) were prepared and used in continuous metathesis reactions using supported ionic liquid (SILP) technology. For these purposes, ring-opening metathesis polymerization (ROMP)-derived monoliths were prepared from norborn-2-ene, tris(norborn-5-ene-2-ylmethyloxy)methylsilane and RuCl2(PCy3)2(CHPh) in the presence of 2-propanol and toluene and surface-grafted with norborn-5-en-2-ylmethyl-N,N,N-trimethylammonium tetrafluoroborate (NBE-CH2-NMe3+ BF4-). Subsequent immobilization of the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM+BF4-]) containing the ionic catalyst 1 created the SILP-catalyst. The use of a second liquid transport phase that contained the substrate and was immiscible with the IL allowed for realizing continuous metathesis reactions. The high turn-over numbers (TONs) of up to 3700 that were obtained in organic solvents in the ring-closing metathesis (RCM) of, e.g., N,N-diallyl trifluoroacetamide, diethyl diallylmalonate, diethyl diallyl malonate, tert-butyl, N,N-diallylcarbamate, N,N-diallylacetamide, diphenyldiallylsilane, and 1,7-octadiene as well as in the self metathesis of methyl oleate could be further increased using biphasic conditions using [BDMIM+BF4-]/heptane. Under continuous SILP conditions, TONs up to 900 were observed. Due to the ionic character of the initiator, catalyst leaching into the transport phase is very low (<0.1%). Finally, the IL can, together with decomposed catalyst, be removed from the monolithic support by flushing with methanol. Upon reloading with [BDMIM+BF4-]/1, the thus recycled support material again qualified for utilization in continuous metathesis reactions.

Since the introduction of click chemistry in 2004, there has been a gradual shift of interest from the copper catalyzed cycloaddition reaction between an azide and an alkyne (CuAAC) to the development of efficient metal-free reactions. The most relevant to be mentioned are reactions with thiols, denoted as thiol-click reactions, thanks to their often excellent click properties. Though thiol-click reactions have proven to be successful in many cases, there are limitations to be kept in mind. Thiols are prone to oxidation reactions, are not widely available and moreover, they usually have an unpleasant smell. Therefore, it can be advantageous to generate thiols in situ and convert them in a one-pot process. The readily available N-acetylhomocysteine thiolactone was already used for the introduction of thiol groups in natural proteins, through the nucleophilic ring-opening by the ε-NH2 groups of lysine residues. We anticipated the ability to adapt this methodology and combine it with the radical thiol-ene process in a one-pot fashion as a mild approach for the synthesis of polymeric architectures starting from stable amine containing compounds. This amine-thiol-ene conjugation as a simple, efficient, and modular linking process is considered to be a relevant extension of the currently quite popular thiol-ene chemistry, especially in polymer science. In a first stage, the one-pot two-step sequence was performed on low-molecular-weight model compounds to determine the reaction kinetics and to analyze the composition of the obtained reaction mixture. Encouraged by the positive results of this model study, we investigated the synthesis of a monomer containing both a double bond and a thiolactone unit, resulting in an AB&’ type monomer. The valorization of the reactivity of this monomer, N-(allyloxy)carbonylhomocysteine thiolac-tone (Alloc-TL), upon aminolysis and subsequent UV-curing, enabled us to develop convenient and accelerated protocols for the synthesis of different polymer structures. Using ethanolamine as nucleophile in the presence of DMPA as photoinitiator, we were able to synthesize functional, linear polymers. Moreover, clear, non-tacky and mechanically stable network films were obtained using the same monomer and a diamine as crosslinker. Thus, we demonstrate the wide range of synthetic possibilities offered by this mild, fast and facile polymerization process.

Conjugated organic polymers are a promising class of materials with applications including organic photovoltaics, light-emitting diodes, solar cells and sensors. Conjugated polymers, such as poly(phenylenevinylene)s, poly(phenyleneethynylene) and poly(phenylenediethynylene), are typically synthesized by classical organic solution-based chemistry. However, incompatibility between the monomers and the polymerization conditions as well as solubility limitations often require utilization of precursor monomers or post-polymerization modifications complicating the synthesis. We envisioned that some of these issues could be avoided by performing the polymerization in the solid state, which completely eliminates problems regarding the solubility. Mechanochemical polymerization in the solid state by ball milling is a method that has been sparingly investigated. Only reports on poly(aniline)1, poly(paraphenylene), poly(thiophene) and poly(pyrrole)2 have been published. Here we report the synthesis of conjugated organic polymers by a mechanochemical method, namely ball milling. Poly(phenylenevinylene)s (PPVs) were prepared by solid state Gilch polymerization. The obtained polymers were characterized by NMR, GPC, IR and UV-Vis. The effects of various ball mill parameters, i.e. milling time and milling speed were investigated. Moreover, the scope and generality of the solid state ball mill polymerization were examined by utilizing monomers containing functional groups incompatible with the solvents required for solution-based Gilch polymerization. 1) Huang et al. Macromolecules 2005, 38, 317-321. 2) Posudevsky et al. Synthetic Met. 2010, 160, 47-51.

Creative design and precision synthesis of organic and polymeric semiconductors provide control over molecular properties such as size, shape, color and donor/acceptor strength. Supramolecular order can be encoded as well and combined with new processing techniques to determine packing in the bulk and at interfaces. A particular challenge is the bottom-up synthesis of graphene from 3D-polyphenylene precursors. Surface immobilized graphene nanoribbons and donor-acceptor polymers with record high FET mobilities are striking examples of precision synthesis for electronic function. With the right molecules in hand, a good case can be made by relating single-molecule and monolayer properties to ensemble devices. Nature 2010, 466, 470; Nature Chemistry 2011, 3, 61; J. Am. Chem. Soc. 2011, 133, 2605; Nature Nanotechnology 2011, 6, 226; Adv. Mater. 2012, 24, 417.

Our research interests include the development of controlled polymer architectures, hybrid nanoparticle assemblies, and the integration of dynamic supramolecular systems onto surfaces. Using cucurbit[n]urils (CB[n]s) we adopt a simple bottom-up approach to achieve sophisticated designs, which are directed at the preparation of novel photonic devices, high-density patterned media, and chemical and biological sensors. Modification of solution viscosity using multivalent polymers and imidazolium based ionic liquids has been accomplished through dynamic cross-linking in water using CB[8]. These hydrogels, with extremely high water content (up to 99.75% water by weight), have also been prepared by utilizing renewable cellulose derivatives. Their rapid formation and shear-induced flow properties make these materials perfectly suited for use as injectable hydrogels for delivery of therapeutics. Indeed, model proteins can be easily encapsulated and their sustained release is observed over the course of 6 months. This far surpasses the current state of the art for protein release from a hydrogel, highlighting these materials as important potential candidates for sustained therapeutic applications. Furthermore, polymer-inorganic composite materials can be readily prepared based on the CB[8] coupling of multivalent gold nanoparticles (AuNPs) to functional copolymers. When these systems are attached onto gold surfaces intricate control is achieved over the site-selective immobilization of colloids and peptides. This has great scope for the development of optical materials, chemical sensors and biological separations. Additionally, we have developed an innovative new technique for manufacturing ‘smart&’ microcapsules in large quantities using continuous flow in a single step from tiny droplets of water. The microdroplets are loaded with copolymers, AuNPs and CB[8]. The major advantage of this manufacturing platform over current methods is that a variety of cargos can be efficiently loaded during the microcapsule formation at room temperature, and the dynamic supramolecular interactions provide control over the porosity of the capsules and the timed release of their contents using stimuli. Our CB[n] based host-guest systems exhibit dynamic self assembly and are capable of responding to stimuli (photochemical, chemical, and thermal) allowing for external control and function to be built into the materials.

Nucleic acid-templated gene replication, transcription, and translation are the molecular essence of creating sequence-defined biopolymers and enabling their evolution. In contrast, a vast majority of synthetic polymers are not created in a manner that allows precise, molecular-level control of polymer sequence and length. With the development of a DNA-templated translation strategy that mimics Nature&’s translation process, we show that the genetic information of DNA can be translated into the defined sequence of synthetic polymers with no structural similarity to nucleic acids. Without recourse to any biosynthetic machinery, our approach enables the sequence-specific translation of DNA into structurally and functionally diverse synthetic polymers with uniform length and molecular weights of up to 26 KDa. This work represents a novel route toward generating a synthetic polymer library containing large-scale sequence information that is capable of undergoing Darwinian evolution. Thus, defined sequence that dictates the specific structure and function, an otherwise unique hallmark of biopolymers, is likely to become an emergent property of synthetic polymers.

Polydiacetylene (PDA) in the form of ordered assemblies such as single crystals, coatings, or liposomes exhibit a chromatic response to a variety of chemical, biological and environmental stimuli. A dramatic blue to red color change is accompanied by an on/off quenching mechanism and dramatic changes in Raman spectroscopic signature peaks, making PDAs a unique and effective sensing system. We have immobilized PDAs onto or within fibers such as cotton or extruded calcium alginate or as coatings on films, such as polyurethane to create simple, easily deployed sensor systems. Functionalized PDAs capable of detecting varied contaminants such as bacterial and chemical toxins are being developed for applications ranging from food safety to smart packaging to responsive wound dressings. The preparation and characterization of new polydiacetylene-containing sensing assemblies, optimization of sensor sensitivity and selectivity, and construction of prototypes for practical sensing applications will be presented.

Motivated by our investigations of polymer mimics for the natural enzyme Silicatein α, we synthesized block copolymers of poly(4-vinyl imidazole). It has been shown that serine and histidine residues are the active amino acid residues for the enzyme, and thus the incorporation of the imidazole functionality (to mimic histidine) was an attractive goal. The imidazole ring is also known for its biocompatibility and its application in ionic liquids. Imidazole based ionic liquids have found various applications such as water treatment agents and green solvents. Copolymers of poly(4-vinyl imidazole) have been shown to exhibit esterolytic activity and both nitrogens in the imidazole ring are available for substitution with alkyl groups. With different combinations of alkyl substituents, properties of the polymer can be tuned to match the demands of particular applications. The incorporation of the imidazole functionality into a macromolecular structures has also been the focus of several previous research studies. Elabd et. al. replaced the methyl group in methyl acrylate with dialkyl imidazole using a quaternization reaction. Gast et. al., incorporated imidazole into a block copolymer by the post polymerization reaction of polychloromethylstyrene and 1-methylimidazole. Long et. al. used nitroxide mediated polymerization to synthesize block copolymers of 1-(4-vinylbenzyl)imidazole and studied their thermomechanical properties and ionic conductivity. Overberger et. al. have synthesized a random copolymer of 4-vinyl imidazole and vinyl acetate for the possible application as proteolytic enzyme. With the availability of block copolymers of poly(4-vinyl imidazole), a new range of applications, such as pH sensitive block copolymers, can be explored. In this presentation, we describe the synthesis of poly(vinyl acetate-b-4-vinyl imidazole) using a controlled radical polymerization method and report the characterization results as well as the properties of this new block copolymer.

Pyrene discovered by Laurent in 1873 is one of the oldest known polycyclic aromatic hydrocarbons and often referred to as fruit fly of all photochemists.[1] Owing to its attractive combination of properties, pyrene has become one of the most studied organic molecules in terms of its photophysical properties. When light emitting conjugated polymers have attracted their attention due to their potential as material for flat panel displays and lighting applications, potential of pyrene in this area has been raised.[2] Latest only red and green, but none blue-emitting conjugated polymers have shown sufficient efficiencies and lifetime to be of commercial value. We found a novel class of pyrene polymers showing deep blue light emission as required for OLEDs and do not exhibit excimer or aggregate emission when processed. Due to the molecular structure the polymer shows excellent solubility and no oxidative degradation processes, such as oxidation or oxidation of aliphatic CH and the conjugated backbone (known for the 9-position of polyfluorene), were detected. Towards novel polymers two pyrene monomers where synthesized via a simple two step, respectively five step chemical route directly from pyrene, for following metal-catalysed polymerization reactions. These two monomeric buildingblocks, namely 1,3-dibromo-7-tert-butylpyrene (tBuPy) and 1,3-dibromo-6,8-di-n-dodecylpyrene (nAlkPy), were then homopolymerised via Yamamoto-type and copolymerized via Suzuki-type polymerization reaction. For the tBuPy we report the highest degree of polymerization for pyrene polymers up to now. GPC analysis against polyparaphenylene-standard (ppp) revealed a number average molecular weight of 29,800 g/mol, a weight average molecular weight of 51,500 g/mol with a polydispersity of 1.7.[3] OLED device fabrication by using pyrene polymers as emitting layer leads to a efficiency of 0.12 cd/A for the homo-tBuPy-polymer and was increased by copolymerization of tBuPy with triphenylamine (TPA) about 58% to 0.19 cd/A with a maximum brightness of 1035 cd/m2 and a quantum yield of Phi;=0.88. The emission peaking at 450nm and corresponding to CIE1931 coordinates are located clearly in the deep blue region of the visible spectrum.[4] In conclusion 1,3-pyrenylene polymers own their remarkable benefit in consequence of a large dihedral angle between the pyrene units, strongly suppressing aggregation and excimer emission. A straight forward synthetic route and high fluorescene quantum yields in thin films gains 1,3-pyrenylene polymers in the center stage for blue light emitting diod devices. [1] Laurent, A. Ann. Chim. Phys. 1837, 66, 136. [2] a) U. Scherf, E. J. W. List, Adv. Mater., 2002, 14, 477-487. b) R. H. Friend, R. W. Gymer, W. R. Salaneck, Nature, 1999, 397(6715), 121-128. [3] T. Figuera-Duarte, E. J. W. List, K. Müllen, Adv. Mater., 2010, 22, 990-993. [4] R. Tratting, D. Lorbach, E. J. W. List, K. Müllen, Optics Express, 2011, 19, 6-18.

Nanoparticles can structurally mimic pathogens and rapidly transport antigen and immunostimulatory adjuvant molecules from injection sites through lymphatics to lymph nodes, making them of great interest as synthetic vaccine vectors. To achieve nanoparticles that combine precise physical characteristics with the manufacturing and scalability advantages of bottom-up systems, we explored the design of well-defined polymeric amphiphiles with the general structure (lipid mimic)-(oligonucleotide)-(cargo), which self-assemble into micelles with tunable stability determined by the presence of a G-quartet-forming guanine oligonucleotide repeat. On injection in vivo, these self-assembled particles enter lymphatics and traffic to lymph nodes efficiently. We found that optimization of the stability of micelles in the presence of serum maximized delivery and capture in the lymph node. In addition, bundling of immunostimulatory cargo molecules by the G-quartet blocks enhanced their immunostimulatory function, allowing immune responses to peptide and protein vaccines to be dramatically enhanced. Application of this approach to enhanced vaccines for infectious disease and strategies for tumor immunotherapy will be discussed.

Medical devices and consumer-exposed surfaces with preloaded active ingredients and controlled release offer fascinating applications.[1] Their action, however, is time-limited due to a non-replenishable stock of reactive compounds.[2] In this work we directly implement the microorganisms synthesizing the reactive compound into flexible polymer surfaces and, thereby combine concepts from biotechnology directly with material science. These functional living materials make use of recently developed artificial biological niches,[3] where a nanoporous top layer constrains microorganism&’s habitat in a 2D geometry. Using various fungi and bacteria strains we show how the evolutionary acquired defense mechanism of penicillin producing fungi is maintained across nanoporous membranes, where it can be used to create surfaces that actively kill susceptible bacteria. The here introduced concept of biotechnological production on site provides a route to complex, adaptive and reprogrammable functional materials with long term sustained release of specific compounds [4].

Current progress in polymer nanocomposites is crucially limited by the strong tendency of nanoparticles to aggregate in polymeric matrices, a complication that also prevents a clear identification of the underlying nanoscale mechanism that leads to the high efficiency of nanocomposites. We discovered that coating nanoparticles with a brush-like polymer layer provides a general and versatile route to fully miscible nanocomposites that show no nanoparticle aggregation over the whole range of nanoparticle volume fractions. [1] In a spherical polymer brush, the polymer chains are attached with one end to the particle surface. The chain ends may be attached covalently, but we found that a more versatile and simpler approach was to attach the polymers via coordinative interactions. We demonstrate the generality of this approach with the preparation of fully miscible metal (Au, Ag), oxide (ZnO, Fe2O3), sulfide (PbS) and selenide nanoparticles (CdSe) having catalytic, magnetic, or semiconducting properties in polymers such as polyethylene, polyisoprene, polystyrene, and polyethylene oxide. Optically transparent materials with nanoparticle weight fractions of more than 40% can be obtained. In miscible nanocomposites nanoparticles assemble into superlattices with unprecedented order, which allows excellent control of the interparticle distance in polymeric matrices relevant for applications in magnetic and photovoltaic devices. [1] S. Fischer, A. Salcher, A. Kornowski, H. Weller, S. Förster, Angew. Chem. Int. Ed. 50 (2011) 7811.

Silk fibroin protein has been of interest for bioinspired applications in field ranging from tissue engineering to optics for a number of years. Its advantages in bio-optical and other technical areas arise from its inherent biocompatibility, ease of doping, excellent mechanical properties, and ~95% transmission of light in the visible regime. In establishing optical components on a silk fibroin substrate, recent work has shown the ability to leverage the mechanical properties of the material to imprint photonic nanostructures using a soft-lithography based technique. The applicability of this imprinting technique is limited however, due to the degradation of the nanofabricated silicon or nickel masters used as pattern templates, and the planar requirement imposed by these masters. Furthermore, the beta-sheet crystallization of the resulting optical components, an important parameter for determining their degradation when biologically interfaced, cannot be induced by this method. In this work, we extend the applicability of the existing silk imprinting technique to imprint subsequent generations of silk films with the first generation of imprints. The ability to use silk fibroin films as masters for soft-lithographic nanoimprinting is derived from the their water dependent glass transition temperature (Tg) In a wet state, silk fibroin has glass transition temperature is close to room temperature, but this rises rapidly as water is removed from the material. Rapidly heating the film above its Tg causes reflow, by which the nanoimprinting occurs. The addition of ~50 Psi of pressure along with the heat helps to drive water from the film, increasing its Tg and locking the imprinted pattern into place. Furthermore, the combination of heat and pressure also induce beta sheet crystallization of the film, rendering it water insoluble. Since a fully dried crystallized film will have a Tg of ~178°C, it can then be used as a master for subsequent imprints. This allows for high throughput fabrication of both positive and negative patterns with a high degree of crystallinity, thereby extending the life the initial silicon or nickel master. Characterization of this method by atomic force microscopy showed the ability to imprint at temperatures as low as 80°C with a one minute process time, but also in times as short as 5 seconds (at 120°C). At least three generations were seen to be possible when using each daughter generation as a master for subsequent imprinting, and at least 18 films can be imprinted per generation without significant loss in quality. In addition, the flexible nature of the silk fibroin films allows for the possibility of curvilinear imprinting, further expanding the applicability of the technique.

Given the low surface energy of poly(3-hexyl thiophene), P3HT, relative to [6,6]-phenyl-C61-butyric acid methyl ester, PCBM, the polymer donor preferentially segregates to the surface of bulk-heterojunction active layers comprising these constituent organic semiconductors. This vertical striation in composition is commonly thought to adversely affect device characteristics of polymer solar cells as preferentially segregated P3HT is now in direct contact with the electron-collecting interface. Using soft-contact lamination and delamination schemes to transfer nominally the same polymer active layers but with an inverted composition profile to the conventional device platform, we show unambiguously that the performance of P3HT:PCBM bulk-heterojunction solar cells are independent of preferential segregation of P3HT at the electron-collecting interface. By inserting P3HT and PCBM thin films having variable thicknesses at the electron- and hole-collecting interfaces, respectively, we further demonstrate an asymmetry in charge transport. More specifically, the insertion of P3HT at the electron-collecting interface retards current flow to a smaller extent compared to the insertion of PCBM at the hole-collecting interface of polymer solar cells. We attribute this asymmetry to differences in the tail state-assisted charge injection and recombination at the active layer-electrode interfaces. P3HT exhibits a higher density of tail states compared to PCBM; holes in these tail states can thus easily recombine with electrons at the electron-collection interface during device operation. This process is subsequently compensated by the injection of holes from the cathode into these tail states, which collectively enables net current flow through the polymer solar cell. It is thus the presence of these tail states in P3HT that is responsible for the invariance in device characteristics with vertical phase separation in the active layers of P3HT:PCBM solar cells.

Fabrication of solid state structures at a nanometer scale on different surface attracts much attention because of its technological importance in nanoelectronics, nanofludics and nanosensors. Recent developments in this filed include, self-assembly and electrochemical nanolithography. However, exploring the strcuture-property relationship of conjugated polymers and patterning ability at different conditions is important to find suitable materials for variosu devices/applications. The current presentation will focus on design, synthesis of novel conjugated polymers, self-assembly and patterning the polymer films using nanolithography techniques. A simple drop casting allows us to develop defect free structures such as honey-combs from polymers. Conjugated polymers are mixed with nanoparticles, fullerenes, carbon nanotubes and quantum dots to develop interesting hybrid materials. The homogenous solutions of such hybrid materials can be self-assembled into patterned thin films and properties of such films are investigated. The presentation will focus on providing sufficient details on synthesis, characterization and potential applications of interesting polymer/composite materials.

Several recent events, including the Deepwater Horizon oil-spill in the Gulf of Mexico, have highlighted the difficulty of effective oil-water separation. Efficient, cost-effective processes for oil-water separation, especially in the presence of dispersants (or surfactants), are greatly desired. Surfactant-stabilized mixtures of oil and water are classified by the diameter (d) of the dispersed phase as: i) free oil and water, if d > 150 mu;m, ii) a dispersion, if 20 mu;m le; d le; 150 mu;m, or iii) an emulsion, if d < 20 mu;m. Conventional gravity separators and skimming techniques are incapable of separating emulsions. Membrane-based technologies are attractive for demulsification i.e., the conversion of an emulsion to a free oil-water mixture, because they are relatively energy-efficient, cost-effective, and applicable across a wide range of industrial effluents. However, for complete oil-water separation, demulsification is typically followed by either gravity separation or skimming. In this work, we have developed superhydrophilic and superoleophobic membranes that allow for the separation of a range of different oil-water mixtures including free oil and water, oil-in-water emulsions, water-in-oil emulsions and any combination of these phases in a single unit operation, with greater than 99.9% separation efficiency. Our separation methodology is solely gravity driven and consequently it is expected to be one of the most energy-efficient separation processes for different oil-water mixtures. Further, our dip-coating based membrane fabrication is easily scalable and we demonstrate the separation of several liters of oil-water mixtures using a scaled up apparatus. In addition, we also demonstrate continuous separation of oil-water emulsions for over 100 hours without a decrease in flux. We envision that our separation methodology will be useful for numerous applications including the clean up of oil-spills, wastewater treatment, fuel purification and the separation of numerous commercially relevant emulsions.

Advanced electronic devices, sensors and actuators that can intimately integrate with soft, time-dynamic tissues of the human body have the potential to bring new and important capabilities to clinical healthcare. Polymer interface materials and substrates, ranging from silicone membranes to bio-polymer sheets, play critically important roles in these technologies. This talk describes electronic systems that laminate directly onto the brain, skin and heart, where precision structures of elastomers and bio-resorbable materials establish interfaces that are matched, in shape and mechanics, to these organs, in a way that provides high quality, non-invasive modes for diagnostic and therapeutic function.

Soft elastic solids placed under compressive stress can undergo a variety of different mechanical shape instabilities, depending on the geometry of the system. In one example, we study the surface ‘creasing&’ instability of thin layers confined in two-dimensions by attachment to a more rigid foundation. We have shown that, in close analogy to classical nucleation theory, formation of creases requires a finite overstrain to overcome the energy barrier provided by surface tension, thus providing great sensitivity to heterogeneous nucleation sites. This allows for precise control over crease locations by the introduction of nucleating features, enabling formation of stimuli-responsive surface patterns. In a second example, we consider the behavior of gel sheets internally constrained in their swelling through lateral variations in crosslinking. A newly developed method for patterning these materials provides access to opportunities for studying the controlled folding and buckling of gel micro-objects.

Materials with controlled thermal expansion have applications in stress control, actuators, sensors, and MEMS/NEMS devices. Traditional approaches to control the thermal expansion of a material include composites combining materials with high and low coefficients of thermal expansion (CTE). Here we have unveiled that the combinations of two materials with high CTE can demonstrate a CTE lower than each alone when molecular control over structure is applied. We have demonstrated that the polyelectrolyte multilayers (PEM) formed by the sequential adsorption of polycation and polyanion layers by layer by layer (LBL) deposition have a lower value of thermal expansion as compared to polyelectrolyte complexes that do not have the molecular scale control over internal structure as allowed with LBL. The same structure creates nanochannels that make the adsorption/desorption of water molecules extremely fast. In this case the material shrinkage associated with the desorption of water due to the corresponding decrease in relative humidity associated with a temperature rise, dominates over the somewhat small CTE creating a pseudo negative thermal expansion (NTE). We demonstrate the presence of this NTE in a three-dimensional (3D) porous structure where increases in humidity (decreases in temperature) should create expansion that provides decreased porosity and corresponding diffusion through the porous structure. In addition, this material property of the PEMs is controllable based on the number of LBL bilayers used to make the 3D structure or through incorporation of nanomaterials such as carbon nanotubes.

Fabrication of spatially controlled molecular structures growing in the third dimension on surfaces is a key challenge of current materials science. Conductive polymer brushes grafted from surfaces, as examples of such structures, are very desirable for e.g. organic photovoltaics and molecular electronics since they would form directional nanoscale pathway for charge transport. However, synthesis of surface-grafted conjugated polymer brushes is still very challenging since there are no controlled polymerization techniques easily applicable for that purpose. The reason is that the polymerization of common vinyl monomers proceeds according to a chain growth mechanism, which is easily adaptable for initiating from surfaces while synthesis of conjugated polymers involves typically a step growth polymerization mechanism (with some rare exceptions), which is not compatible with “grafting from” approach. We report here self-templating surface-initiated polymerization (ST-SIP) leading to synthesis of ladder-like brushes with one chain in a pair being conjugated. Iniferter-based photopolymerization was applied to obtain the macromonomer brushes grafted from gold surface and containing acetylene side groups. The prealigned groups were subsequently reacted using Rh-based catalytic polymerization forming polyacetylene chains. Such obtained brushes after doping exhibited high conductivity in the direction perpendicular to the surface as showed using conductive atomic force microscopy. The general route presented here may be easily applied for the synthesis of other polymer architectures comprising conjugated polymers (mixed brushes, block conductive-nonconductive brushes etc.). Acknowledgement: The authors would like to thank Polish Ministry of Science and Higher Education for the financial support (“Ideas Plus” grant no. IdP2011 000561).

Biomaterials implants and devices play an increasing role in an ageing society for the restoration of human function, but often fail due to biomaterials associated infections. Biofilms resist antibiotic treatment and therefore infected implants or devices usually have to be replaced. Various surface modifications have been developed to improve the surface properties of medical implants and devices, as e.g. polymer brush coatings known for their superior anti-adhesive properties. This study shows the influence of mono-, bi- and multifunctional polymer brush coatings on silicone rubber on bacterial adhesion, biofilm formation and tissue cell integration. For the bi- and multifunctional coatings the polymer chains have been conjugated to various antimicrobial compounds and tissue cell adhesive moieties. Adhesion forces measured using atomic force microscopy of nine common causative bacterial strains in biomaterials associated infections, including Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa were significantly smaller on polymer brush-coated silicone rubber compared to the uncoated surface. Bacterial biofilms on polymer brush coatings developed more slowly and formed scattered colonies which remained more in a planktonic state. This biofilm was susceptible for gentamicin treatment, opposite to compact biofilms formed on uncoated silicone rubber showing antibiotic resistance. A bifunctional polymer brush coating was created by conjugation of the antimicrobial protein, lysozyme, to the polymer molecules giving the brush dual functionality i.e., resistance to bacterial adhesion and lethal to the few bacteria which adhere. The brush conformation of the conjugates on the surface was analyzed by quartz crystal microbalance with dissipation analysis and X-ray photoelectron spectroscopy and indicated surface coverage by lysozyme. The antimicrobial activity of the coating was demonstrated against the model bacterium Bacillus subtilis and the coating with a 1% pluronic-lysozyme conjugate proved to be more bactericidal than the coating having a 100% Pluronic-lysozyme conjugate. A multifunctional coating was created by adhesion of antimicrobial peptides and RGD-peptides conjugated to the polymer chains together with unmodified polymer molecules on the surface. Such coatings exerted anti-adhesive activity due to the polymer brush, antibacterial activity due to the antimicrobial peptide and maintained good tissue integration due to the presence of RGD-peptides.

Precision synthesis of polymer brushes combined with their patterning makes a very powerful took for surface modification. Polymer brushes provide remarkable screening power in shielding a substrate from the environment through both steric and charge interactions. We have recently explored the effect of brush composition and thickness on non-specific binding and cellular attachment. Several polymer brush systems are described to control interaction of biomacromolecules and cells by design of specific and non-specific interactions in polymer brush architectures. “Grown from” and block copolymer brushes are described, both of which provide excellent substrates for study of brush surfaces. We also report the direct patterning of multi-component block copolymer brush systems. Positive-tone/negative-tone block copolymer brushes have been patterned by electron beam lithographic methods to produce micro- and nanostructures. We have analyzed these systems through varying the polymer brush thickness and investigating different solvent development conditions. Direct patterning of positive-tone/positive-tone block copolymer brushes were also carried out. Their phase separation and morphologies in the patterns was found to be affected by both feature size and development environment. Examples of polymer brushes used for sensor creation and for investigation of cellular interaction are provided. Brushes used in non-fouling coatings tailored for marine applications and in which amphiphilic structures play an important role are also described.

Surfaces and particles coated with poly(N-isopropylacrylamide), pNIPAAm, brushes are well suited to become important components in nanoscale devices for drug delivery and gating. One reason is that pNIPAAm exhibits at lower critical solution temperature (LCST) near body temperature, above which the hydrated polymer collapses and expels water. However, for use in drug delivery and gating, it is important to understand the molecular-level effect of small-molecule additives (e.g., loaded drugs) on surface-tethered pNIPAAm, because the distribution of the additive and its effect on the LCST behavior is critical to functionality. Most studies on pNIPAAm loaded with additives focus on cross-linked gels and linear chains in solution, and do not reveal information about the spatial distribution of the additive on the molecular level. Neutron reflectometry (NR) provides the density profile of a material normal to the substrate surface with angstrom-scale resolution. We use NR in this study to evaluate structural changes in the pNIPAAm brush as a function of temperature upon loading with Isoniazid, a small molecule drug. We characterize the loading and distribution before, during and after the collapse of the brush. Our results indicate that 1) the additive delays the onset of the LCST, 2) it increases the height of the brush before, during and after the collapse, 3) it is homogeneously distributed throughout the brush, and 4) it is retained inside the brush even when water is expelled at high temperature. The results show that the small molecule has no preference for either the substrate or the brush/water interface, and suggest strong binding between the small molecule and the polymer.

Effective adhesion between similar or dissimilar materials has become one of the most critical technical prerequisites for advanced manufacturing at ever-smaller scales. Inspired by the superior properties and structures of biological organisms such as gecko adhesive “hairy” toe pads and lotus superhydrophobic anti-adhesive leaves, we report our recent progress of using well-defined micro-patterned surfaces for controlling adhesion properties of polymeric materials. The biological micro/nano-structures are modeled as micro/nano-pillars whose geometrical features (e.g. size, shape, aspect ratio) and surface chemistry (e.g. polarity, surface energy) are key design parameters. The spatular or laid contact adhesion studied by indentation tests showed the reduction of adhesion by surface patterning with low aspect ratio structures. The condition of high number density and/or high aspect ratio is necessary for high adhesion but creates the risk of fibrils bundling owing to the adhesion between fibrils. A thin film-terminated structure can help to overcome this problem and increase adhesion as well. A hybrid adhesive structure consisting of an array of elastic biomimetic micropillars and a thin viscoelastic terminal film was designed and fabricated. A remarkable adhesion enhancement and crack propagation modulation were observed, indicating a synergistic effect between the elastic fibrillar structures and viscoelastic terminal film. In contrast to the spatular contacts, the conformal adhesion at interface can be enhanced significantly by creating micro-patterns to form a “zipped” composite interface; the enhancement monotonically increases with the aspect ratios, where the side-wall friction plays an important role.

Compatibilizing ligand-capped nanoparticles (NPs) with polymer matrices has been a significant challenge in nanocomposite science and engineering. Traditionally, the controlling parameters are the surface ligand chemistry, graft density, and grafted chain to matrix molecular weight ratio. To achieve optimum properties, these parameters should be varied to reduce the strong van der Waals attraction between NP cores, while maximizing the entropic wetting or entanglement of the matrix with the surface molecules. However, there is a delicate balance between sufficient enthalpic screening and favorable entropic wettability. In addition, if functional surface ligands are added, a sacrifice between functionality and compatibility has to be made. Here, we demonstrate a novel approach for 1) achieving good grafted NPs dispersion while maintaining matrix entanglement, and 2) adding functionality while maintaining good dispersion. We have achieved this using mixed bimodal polymer brushes, consisting of two chemically distinct polymer brush species with significantly different molecular weights covalently tethered to the surface of NP cores. Silica NPs with densely grafted polystyrene (PS) short brush and sparsely grafted poly(methyl methacrylate) (PMMA) long brush are used as a model system, and their dispersion and wettability in both PS and PMMA matrices are characterized. It was found that mixed-bimodal-brush-grafted NPs can be well dispersed in PMMA even though the PS short brush is immiscible with the matrix. This good dispersion was accompanied by an increase in glass transition temperature suggesting good wettability of the matrix and particle. The short brush at high graft density enthalpically screens the NP core-core attraction, which is critical for good dispersion, while the long brush with low graft density provides entropic contributions, including excluded-volume induced dispersion and entanglement of the brush and matrix. In addition to enhancing our ability to tune the NP / polymer interaction, chemically distinct short brushes can be independently used to add functionalities such as conductivity and florescence to the polymer nanocomposite.

A bird eye view of any folded protein shows a complex surface composed of hydrophobic and hydrophilic patches closely packed. To date little is known on the fundamental properties that such packing determines. In this talk I will present my group&’s endeavor into the synthesis, characterization, and understanding of a family of nanomaterials (mixed monolayer protected nanoparticles) that posses a surface coexistence of patches of opposite hydrophilicity resembling that present on folded protein. I will show that these materials are ideal model compound to uncover the basic properties that such coexistence determines at the solid liquid interface, and will conclude with example of application of these nanoparticles when used as ion sensors.