Similar to conventional lipids also suitable amphiphilic block copolymers may self-assemble in aqueous media to lyotropic liquid crystalline phases and - in diluted solution - membrane-like superstructures. Of particular interest are amphiphilic diblock - and triblock copolymers based on a combination of hydrophilic (e.g., poly(2-methyl oxazolines)) and hydrophobic (e.g., PDMS) chains. The physical properties of these membranes can be controlled to a large degree via the molecular weight and the hydrophilic-to-hydrophobic block length ratio of these polymers. Compared to conventional low molar mass building blocks (e.g. lipids), membranes based on macromolecular self-assembly, not only have the advantage of superior stability and toughness, but in addition offer numerous possibilities of tailoring physical, chemical and biological properties since many functions can be implemented simultaneously in one single macromolecule. Moreover, other well-defined functions such as recognition, cooperativity, regulation, replication, and catalysis can be introduced by combining these superstructures with suitable functional units from Nature, e.g., by incorporation of integral membrane proteins. Recently we used this concept to prepare polymer nanoreactors by encapsulating water-soluble enzymes inside the aqueous compartments of block copolymer vesicles. Channel proteins were used to selectively control the exchange of substrates and products with the environment. By introducing appropriately derivatized (e.g. biotin, thiol etc.) polymers we succeeded to immobilize intact block copolymer vesicles and functional nanoreactors on solid supports. Successful immobilization of intact nanoreactors has been monitored by confocal fluorescence microscopy), QCM-D, imaging ellipsometry and AFM. Immobilized polymer nanoreactors were used as chemically and mechanically stable, nanometer-sized compartments to follow folding/unfolding of single proteins and to monitor enzymatic reactions down to a single nanoreactor scale. Model reactions were used to demonstrate the potential of these structures for biosensing and the local production of bioactive compounds. In addition these nanometer-sized (bio-) reactors that can be targeted to predefined cells. After cellular uptake they retain their function over extended times inside the living cells thus acting as a sort of an artificial organelle that continuously exchanges molecular information with the host organism. This opens new ways for controlled drug delivery and intracellular sensing.

Dynamic interactive systems are defined by networks of exchanging and reversibly connected objects (supermolecules, polymers, biomolecules, biopolymers, pores, nanoplatforms, surfaces, liposomes, cells). They operate under natural selection to allow spatial/temporal and structural/functional adaptability in response to internal constitutional or to external stimulant factors. Herein we will discuss some selected examples of hybrid organic/inorganic systems materials (SYSMAT), covering (a) the sol-gel resolution of constitutional architectures from dynamic combinatorial libraries and (b) the generation of dynamic hybrid materials and systems membranes (SYSMEM) able to evolve inside pore functional architectures via ionic stimuli, so as to improve membrane transport functions. 1.M. Barboiu, Chem. Commun., 2010, 46, 7466-7476. 2.M. Barboiu, S. Cerneaux, G. Vaughan, A. van der Lee, J. Am. Chem. Soc. 2004, 126, 3545-3550 3.C. Arnal-Herault, M. Michau, M. Barboiu, Angew. Chem. Int. Ed. 2007, 46, 8409-8413. 4.C. Arnal-Hérault, M. Barboiu, A. Pasc, M. Michau, A. van der Lee, Chem. Eur. J. 2007, 13, 6792 5.C. Arnal-Herault, A. Pasc-Banu, M. Barboiu, Angew. Chem. Int. Ed. 2007, 46, 4268-4272.

A biomimetic membrane with glycocalyx-like surface has been fabricated by a chemo-enzymatic method. First, hydroxyl groups were introduced onto the surface of microporous polypropylene membrane (MPPM) by UV-induced graft polymerization of oligo(ethylene glycol) methacrylate (OEGMA). Then, glycosylation of the hydroxyl groups with galactose (Gal) was achieved via an enzymatic transglycosylation by β-galactosidase from A. oryzae. XPS spectra clearly show the signal of the anomeric carbon atom of Gal residues on the modified MPPM surface. Lectin adsorption assay was carried out using fluorescence labeled RCA120 on which Gal-specific receptors are present, and fluorescent imaging reveals the initial lectin adsorption (within 2 h) on the Gal-glycosylated MPPM surface is greater than that on the POEGMA-modified and nascent MPPM surfaces. Further more, SEM pictures show that both the UV-induced graft polymerization and enzymatic transglycosylation do not dramatically alter the membrane surface morphology (porosity and pore structure). At the same time, either the POEGMA-modified or the Gal-glycosylated MPPM have good wettability, and the rate of water penetration on the Gal-glycosylated MPPM was higher than that on the POEGMA-modified one. This enzymatic transglycosylation is a promising (simple and “green”) procedure, however, it is important to point out that due to the hydrolysis of glycosidic bond, the amounts of introduced Gal residues are insufficient and thus there is much room for further improvement. Anyhow, this novel chemo-enzymatic method would be expected to have wide applications for the surface modification of membranes with biomimetic properties.

Stimuli-responsive responsive polymers are an interesting class of materials with many (potential) applications. Their common feature is that a chemical or physical stimulus (e.g., the presence of a chemical substance or an electromagnetic field) leads to large and reversible changes of properties. The focus here is on polymeric membranes where stimuli-responsive hydrogel layers or volume structures change the membrane surface properties or barrier structure [1]. Of interest for porous barriers is the interplay between pore size of the base material and extent of thickness or volume change, i.e., a typical response of hydrogels which are sensitive to changes of temperature, pH, the presence of certain ions or molecules, etc. This behavior can be used to reversibly change the barrier properties of a porous membrane; resulting functions are gated membranes, or ultrafiltration membranes with tunable pore size. The responsive behavior can, however, also be used to improve the cleaning efficiency of membranes; this relies on the reversible change in swelling / mobility of intrinsically low-fouling, “protective” functional hydrogel layers on the membrane surface. We have systematically investigated such systems based on track-etched capillary pore membranes with base pore diameters between 10 µm down to 30 nm, in combination with various surface-initiated grafting or pore-filling techniques (e.g., [1-3]). We will present examples for temperature-responsive ultrafiltration membranes with efficiently switchable permeabilities and size-selectivities based on the well-known poly(N-isopropylacrylamide) (PNIPAAm) as grafted layer or pore-filling hydrogel. We will also demonstrate that such membranes can be made responsive to “remote control” by an external electromagnetic field by using co-immobilized superparamagnetic nanoparticles as local heaters within the pores. Molecular imprinting during in situ polymerization of PNIPAAm-based hydrogels in combination with pore-filling can be used to tailor membranes where the permeability is modulated by the presence of certain molecules, e.g., specific proteins. Beyond such studies with model base membranes, examples for the functionalization of industrially established polymeric base materials toward switchable separation membranes will also be discussed (cf., e.g., [4,5]). [1] Q. Yang, N. Adrus, F. Tomicki, M. Ulbricht, J. Mater. Chem. 2011, 21, 2783. [2] A. Friebe, M. Ulbricht, Macromolecules 2009, 42, 1838. [3] N. Adrus, M. Ulbricht, J. Mater. Chem. 2012, 22, 3088. [4] P. D. Peeva, T. Knoche, T. Pieper, M. Ulbricht, Ind. Eng. Chem. Res. 2012, 51, 7231. [5] H. H. Himstedt, Q. Yang, L. P. Dasi, X. Qian, S. R. Wickramasinghe, M. Ulbricht, Langmuir 2011, 27, 5574.

Membrane-based separation is one of the key technologies in producing affordable clean water for industry and our daily life. Tailor-made membranes with a thin selective layer possessing uniform pores and active surfaces are eagerly demanded to ensure the separation processes both a high flux and a high selectivity. Block copolymers (BCPs) are promising materials for the rational design of thin advanced membranes since they self-assemble into nanoscopic domain structures characterized by well-defined feature sizes. Increasingly more efforts have been devoted to develop BCP-based membranes with both high selectivity and high permeability. Most preparative approaches yielding mesoporous BCPs require chemical degradation of one of the blocks of the BCP or extraction of additives (small molecules or homopolymers) incorporated in the domains of one block. As a result, the mechanical stability of the mesoporous BCPs deteriorates, and waste solutions, which are often toxic and/or corrosive, are produced. Moreover, only a limited number of BCPs containing degradable moieties can be employed in this approach and be converted to porous materials via chemical reactions specific to the nature of the BCPs themselves. Nevertheless, only little efforts have been devoted to develop alternative routes to mesoporous BCP membranes, and those reported so far, such as nonsolvent-induced phase separation, usually suffer from relatively poor controllability. In this work, we report on an environmentally friendly, nondestructive approach to produce mechanically stable BCP-based membranes with tunable separation properties. In this approach, amphiphilic BCP films were coated on macroporous supporting membranes, and were submerged in a bath of a swelling agent to generate mesopores in the BCP layer via the selective swelling mechanism, resulting in a composite membrane with the mesoporous BCP as the size-selective layer and the macroporous membrane as the robust supporting layer. After the completion of the selective swelling-induced mesopore generation, the BCP can simply be withdrawn from the swelling agent that can immediately be reused for the next sample. It is even conceivable to design selective swelling-induced mesopore generation as a continuous production process. The membranes were able to discriminate nanoparticles with similar sizes, e.g. they provided a 100% separation of 10-nm gold particles from its mixture with 2-nm gold particles. Moreover, due to the immigration of the polyelectrolyte-natured blocks onto the pore wall, the resulting membranes possess an intrinsically active surface with enhanced hydrophilicity, fouling resistance, and even a stimuli-response function.

Membrane proteins display a wide range of functionality, including sensing, signal transduction, and selective transport of ions and molecules, making them of high technological interest. However, such membrane proteins are generally highly hydrophobic, making them challenging to process and difficult to integrate into synthetic materials and devices. One membrane protein of particular interest is proteorhodopsin, which functions as a light-activated proton pump in marine bacteria to store energy by establishing a proton gradient across the cell membrane. By careful control of synthesis and processing conditions, a solution-based method can be used to incorporate proteorhodopsin into nanostructured hybrid silica-surfactant membranes during self-assembly. Nanostructured hybrid silica materials are advantageous for incorporating proteins because they have high internal surface areas (500-1000 m2/g), controllable periodic ordering, uniform and controllable channel dimensions (5-12 nm), and are chemically, thermally, and mechanically robust. High concentrations (55 wt%) of proteorhodopsin can be achieved in such membranes of arbitrary sizes and thicknesses and with high degrees of nanostructural ordering. The incorporation, nanoscale structures, interactions, and light-stimulated conformational changes and activity of proteorhodopsin in these hybrid membrane materials are established by complementary analytical techniques, including small angle X-ray diffraction, optical absorption spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy of proteorhodopsin containing site-specifically attached spin labels. The incorporation of functional light-harvesting molecules, such as proteorhodopsin, within nanostructured oxide membranes is expected to enable diverse optical and energy conversion applications. The prospects for light-activated ion transport will be specifically discussed.

Stimulus-responsive membranes have been explored for decades for liquid separations or controlled release applications yielding materials whose permeability varies based on a bulk stimulus such as, pH, temperature, light, or an electrical or a magnetic field. However, mimicking the specific and locally acting molecular recognition mechanism found in Nature, which consists of triggering a change in permeability through a specific target-receptor interaction, remains a challenge. Here, self-assembled stimuli-responsive interfaces are reported which are based on DNA-aptamers [1]. These gating membranes respond upon a molecular recognition of a relatively small molecule, adenosine-triphosphate (ATP) rather than a bulk stimulus such as temperature or pH. This work will highlight both the capacity of DNA-aptamers for triggering permeability or controlled release, as well as the characterization techniques employed for elucidating and verifying their function and dimensions of the respective conformational changes. For characterizing the latter, characterization techniques such as quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and dual polarization interferometry (DPI) will be discussed. The main emphasis will rely on how macroscopically observed mass transport phenomena can be correlated with experimental evidence obtained on the molecular scale using these techniques. It will be shown that DNA-aptamer based gating membranes are promising tunable separation barriers or controlled realease interfaces due to the fact that aptamers as acting receptor molecules can be selected toward virtually any kind of target, ranging from small molecules to proteins and even cells, and therefore present an ample range of possible applications such as in biomedicine or bioseparations. 1.Özalp, V.C., and Schäfer , T. Chem. Eur. J., 17(36), 9893-9896, 2011

Ultrafiltration is used for protein concentration and buffer exchange throughout the biotechnology industry, both for the conditioning of the feed between other unit operations and in the final product formulation. The performance of these membranes can be characterized by the trade-off between the membrane permeability and selectivity; membranes with high permeability tend to have low selectivity while membranes with high selectivity tend to have low permeability. This talk will examine current efforts to significantly improve the performance characteristics of ultrafiltration membranes and the opportunities for using these membranes for high-resolution separations. High performance ultrafiltration membranes were generated by covalent attachment of both charged and zwitterionic ligands to a base cellulose membrane. The charged membranes provide high retention of like-charged proteins, with the retention properties determined by both the charge density and the detailed chemistry of the charged ligand. For example, the use of a ligand containing multiple amine groups provided more than a two order of magnitude increase in the retention of cytochrome c, a small positively charged protein. The use of zwitterionic ligands provided very low fouling surfaces due to the high degree of water structuring generated by the combination of the positive (amine) and negative (sulfonic acid) moieties. These charged ultrafiltration membranes can be used to purify a variety of protein products. Specific examples are shown for the purification of pegylated proteins produced by the covalent attachment of a PEG chain to the base protein. Charged membranes can be used to remove the unreacted PEG, and they can also effect the separation of multiply-pegylated species from the desired singly-pegylated product. These results clearly demonstrate that the proper selection of membrane surface charge can provide significant improvements in ultrafiltration performance providing new opportunities for the use of ultrafiltration in the purification of high-value therapeutic proteins in bioprocessing applications.

Polyethersulfone (PES) membrane has been widely used as membrane for biological filtration processes, such as hemodialysis. However, PES membrane surface is sensitive to organic solvent which subsequently causes membrane fouling. In this work, we modify the surface of a nanoporous PES membrane by deposition of a parylene film. Parylene has been widely applied on the biomedical microdevices; however, it was found to form non-porous films that clog the nanoporous of PES membrane. Hence, it is necessary to develop processes for parylene deposition that allow the modification of a membrane surface while keeping the nanopores open. Our modified process uses glycerin vapor that passes through the membrane pores during parylene deposition to align the pores of the PES membrane with those of the parylene film when the parylene thickness was sufficiently small. It was experimentally found that this method prevented parylene from forming over the pores, resulting in membrane having higher diffusion values compared with those prepared conventionally. In this work, the diffusion tests were conducted in a diffusion chamber with the membrane clamped between the NaCl solution and pure water to determine the permeability of the PES membrane before and after deposition. The bare PES membrane gave the highest diffusivity among the membranes due to the lack of any surface coating. In the conventional deposition process, random deposition of parylene may block some of the membrane pores and prevent permeation, resulting in a lower diffusion coefficient. In contrast, the PES membrane coated using our modified deposition process had a higher diffusion coefficient. We believe this is due to improved alignment of the pores of the parylene and PES membrane as a result of glycerin vapor passing through the membrane pores during deposition. In order to validate the presence of deposited parylene, we performed water contact angle measurements on the modified surface of PES membrane. The water contact angle of the bare PES membrane was 49.6°, and increased to 67° - 88° after parylene coating depending on the amount of deposited parylene, which confirmed that indeed parylene coated the PES membrane surface. The findings of this work could potentially be beneficial for ultrafiltration applications.

Portable dialysis systems are expected to drastically improve quality of life (QOL) of the patients who must undergo dialysis treatments for four hours several times a week. Wearable artificial kidneys which consist of filters, pressure sensors and pumps etc. have previously been proposed, but they are still too bulky to use due to the large volume of the filters in them. Our group has been developing micro fluidic systems containing three biocompatible materials; there were nano-porous polyethersulfone (PES) membranes, titanium channel layers whose thickness was two hundred micron and polydimethylsiloxane (PDMS) cover for preventing liquid leakage. In our previous research, the device was evaluated in the single-pass system, in which two different solutions were poured to the device by syringe pump, using pure water and aqueous solution of urea. At that time, we found that there need forty eight mm cube filter to substitute it for human kidney. But we did not focus on “the long term use” and the device was far from practical one. In this paper, we proposed a loop system using the cattle blood and dialysate, focusing on long term use. In the system, there were the micro filters, whose membrane had 166 mm^2 area and 0.8 mm thickness, a peristaltic pump and flow sensors. At first, the concentrations of solutes in blood were adjusted as followings; sodium was 140 mM, potassium 7.5 mM and BUN (urea) 140 mg/dL. Each concentration in dialysate was respectively about 140 mM, 2.0 mM and 0 mg/dL. Blood and dialysate were poured to the device repeatedly by peristaltic pump for forty eight hours at 2.0 mL/min in the flow rate. There were some gap of concentration between blood and dialysate, and thus solutes were allowed to diffuse through our PES membranes (sodium had no gap and no diffusion). As a result, we found that potassium and urea diffusivity through the membrane were respectively 4.5×10^(-10) m^2/s and 5.1×10^(-10) m^2/s. In addition, there was no fouling on the surface of PES membranes.

The sustainable manufacturing of next generation industrial products with target size, composition, structure and function, needs new production concepts. In particular, precise, selective and flexible formulation, conversion and separation processes operating on a molecular level, able to maximize mass and energy utilization minimizing resources utilization and waste production are needed. Membrane emulsification is capable to assist the assembly of a variety of products, such as nanostructured bio-hybrid components (droplets, microspheres, microcapsules) with target particle size and size distribution, complex 3D biomimetic structures, encapsulated formulations. The technology has unique feasibility for formulations containing active labile macromolecules. In fact, the mild conditions used to achieve the drop-by-drop dispersion of immiscible phases into another can preserve biomolecules from denaturation. All these aspects are crucial to meet the demanding requirements for new, diverse, stable and efficient high value-added biomimetic formulations. In this work, the powerful of the methodology in terms of micro-manufacturing precision and information at molecular level will be highlighted. In particular, its capability to assist the preparation of highly uniform oil-in-water microspheres containing lipase self-assembled at the interface and the evaluation of molecular properties of lipase at the interface will be illustrated. For example, from uniform size distribution formulations the dynamic diameter of molecules assembled at the interface can be determined on the basis of easily measurable parameters, such as sphere diameter, oil phase volume dispersed and molar mass present at the interface. In fact, from the sphere diameter, measured by light scattering, the sphere surface area and the sphere volume can be calculated; from the total oil dispersed volume and sphere volume the number of spheres can be obtained; this value combined with the surface area of each sphere gives the total surface area occupied by the lipase; the number of lipase molecules distributed at the interface is simply calculated by the Avogadro number on the basis of lipase moles obtained by mass balance between initial and final molar lipase concentration in water phase. Knowing the number of molecules distributed on the spheres surface area, the dynamic diameter of lipase at the interface can be easily determined. The comparison of molecular diameter data in solution with crystallographic data confirms the robustness of the methodology.

G-protein-coupled receptors (GPCRs) represent the largest family of membrane proteins and an important target for pharmaceuticals. GPCRs are involved in the signal transduction of a wide array of psychological processes including neuronal signaling to immune and hormonal response. Despite being such an important pharmaceutical target, only a handful of GPCR structures have been resolved, albeit in the GPCRs' inactive state by X-ray crystallography. A detailed structural and functional understanding of the GPCR is required for rational design of therapeutics tailored towards finding cures for the diseases caused by GPCR malfunctions. The key challenge facing GPCR characterization is the protein sample preparation involving receptor protein purification and reconstitution while maintaining functional activity. In order to provide an interface for selective reconstitution of the receptor protein to the surface with minimal nonspecific protein adsorption, we are employing organic synthesis strategies to design thiol-based “chemical hooks” to provide optimal control of the orientation, stability and coverage of the GPCR to the surface. Furthermore, we are fabricating highly conformal platinum nanotubes inside commercially available anodic alumina membranes using atomic layer deposition (ALD). We are developing ALD process conditions for conformal platinum coating by tuning the precursor exposure times, and subsequently monitoring the cross-sections of membranes using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The surface of metal nanotubular membranes is modified with self-assembled monolayers (SAM), followed by extrusion-assisted detergent-solubilized GPCR immobilization. Surface functionalization, protein immobilization, and protein/lipid molar ratio inside the nanopores have been analyzed by X ray photoelectron spectroscopy, solid-state NMR, UV-Vis spectroscopy, and fluorescence microscopy. The initial GPCR under investigation is human cannabinoid receptor, CB2, and a range of structural characterization techniques including neutron scattering and solid-state NMR will be employed to investigate the detailed structural and functional information. This nanostructured biointerface provides a large surface area for GPCR immobilization required for high-resolution NMR measurements, and enhances the neutron scattering for small-angle neutron scattering (SANS) experiments.

Ultrathin (5-50 nm thick) silicon membranes represent a new class of porous membrane with a growing number of applications to biology and medicine. Molecular scale thinness enables extraordinary permeability and high separation resolution while the silicon platform enables the miniaturization of separation processes chip-based devices. This presentation will review the fabrication and performance characteristics of ultrathin silicon membranes before describing several devices we are making for biomedical applications. The devices presented will include: 1) and improved in vitro model of the blood-brain barrier; 2) a shear-free chemotaxis chamber for studying cell migration; and 3) a cell-phone-sized blood dialyzer.

Silicon materials possess a great potential in membrane applications thanks to their ability to be easily functionalized and it has been previously pointed out as the perfect membrane material for molecule separation, being much more effective than any conventional polymer counterpart [Berg A. et al, Nature 445, 726, 2007]. Applications range from medicine to filtration and separation. New efforts are being carried out to implement manufacturing techniques for their mass production. We present a simple highly manufacturable process based on standard semiconductor microfabrication techniques to produce silicon based membranes with adjustable size, pore size and density for a great variety of materials. We have produced membranes out of silicon, amorphous silicon and silicon dioxide to demonstrate the versatility and adaptability of our process. Relying on standard chemical and physical etching and deposition steps, the process consists of creating vertical channels (or pores) into the material, followed by isotropic etching to release and peel off the top layer from the original substrate. In case of amorphous silicon, a 5 µm layer of material is deposited on top of a buried oxide layer, which can be used to facilitate the release process. After the pores are created by reactive ion etching, the membrane can be released using hydrofluoric acid based etchant to remove the underlying oxide. This same method can be extended to a great variety of materials for their study as potential materials in membrane applications. Silicon dioxide requires a different and simpler approach where we only need to deposit a thick layer of oxide (2 µm) on top a silicon wafer. Then, we generate the pores and etch away the silicon underneath the oxide so it can be freed and separated from the substrate. Care need to be taken due to the stress generated during deposition which can produce the film to roll up after release. To overcome this issue an annealing step at high temperature might be required. In the case of mono-crystalline silicon, we have developed an alternative method where we only use a low-cost but the most widely used silicon (100) wafer and introduce the formation of spacer-based pore protection so we are able to avoid the use of a buried oxide layer. This process has been described in a previous publication [Rojas J. et al, MEMS12, 281, 2012]. The pores can be defined by standard lithography techniques to achieve specific densities and micrometric dimensions in a controllable and regular fashion with mass production capabilities. Thickness can be easily defined by controlling the amount of material deposited and the depth of the channels etched into the substrate. We have reproducibly fabricated membranes with a pore size of 5 µm regularly separated 5 µm between them, 5-20 µm in thickness and 18 cm² of size. For future work, we envision the use of techniques such electron beam lithography, which can be used to achieve nanometric pore dimensions.

In recent years, porous Si (PSi) has emerged as a promising nanomaterial for biosensing applications. Common PSi-based optical biosensors consist of thin films of either nano-pores (less than 20 nm) or meso-pores (20-100 nm) that are much smaller than the optical wavelength and facilitate mass transport of a range of biological targets including small molecules, DNA, and proteins. However, this detection scheme is not applicable for targeting large biological species (~0.5-2 µm) such as living cells and viruses. Alternative approaches monitor changes in the intensity of the reflectivity spectrum upon direct capture of larger cellular targets on top of the biosensor surface. However, these types of sensors are limited as specific binding events induce predictable changes in the intensity of reflectivity spectrum only. Our work focuses on the design and synthesis of a new optical biosensor based on a two-dimensional (2D) lamellar photonic grating for rapid bacteria detection. The biosensor consists of a 2D periodic structure of macro-PSi with a characteristic pore diameter of 1-3 µm, to allow facile entrapment of the bacteria cells inside the pores. In turn, the captured bacteria induce a change in the effective optical thickness (EOT) of the grating that is monitored and quantified via reflective interferometric Fourier transform spectroscopy (RIFTS). We show that monitoring changes in the optical interference spectrum of the macro-PSi sensors enables a simple and sensitive detection scheme of bacteria. Our preliminary optical studies demonstrate the applicability of these lamellar gratings for the detection of E. coli K-12 bacteria. We show that upon proper design, this novel biosensing scheme allows simultaneous measurements of EOT and reflectance intensity changes. Our preliminary results demonstrate a detection limit of 105 cell/ml for E. coli. It is important to note that no affinity capture molecule is used in these preliminary experiments to bind the E. coli to the PSi. Current experiments explore the use of specific antibodies with high affinity for E. coli to capture and concentrate bacteria inside of the pores and achieve higher detection sensitivity. This proof of concept work provides a generic sensing platform that is applicable for rapid detection and identification of a variety of microorganisms.

Bone tissue engineering typically involves the use of porous, bioresorbable scaffolds to serve as temporary, three-dimensional scaffolds to guide cell attachment, differentiation, proliferation, and subsequent tissue regeneration. Recent research strongly suggests that the choice of scaffold material and its internal porous architecture significantly affect regenerate tissue type, structure, and function. In addition to possessing the appropriate material composition and internal pore architecture for regenerating a specific target tissue, scaffolds must also have mechanical properties appropriate to support the newly formed tissue. In this study we developed a composite membrane scaffold by using a biodegradable polyester, Polycaprolactone (PCL), with hydroxyapatite (HA), which is the main mineral component of bone in order to obtain bone substitutes with structural similarity to the mineral phase of bone and osteoconductive and bone binding properties. Composite membrane scaffolds at different concentration of PCL were prepared by phase inversion technique. PCL-HA membrane scaffolds were obtained from a starting polymeric solution mixed with a bio-ceramic dispersion. A quantitative description of the starting polymeric solution was done to evince the solubility characteristics and the demixing behaviour of PCL/Acetone system, using the thermodynamics principles, which are most important for all phase inversion process. After preparation, membrane scaffolds were characterized in order to evaluate its morphological, physico-chemical and mechanical properties and then used for the cell culture. Our experimental design consists to apply the knowledge of natural bone tissue remodelling in an in vitro membrane biohybrid system. It has been shown that osteoclasts and their progenitor monocytes may influence bone forming cells by labelling the resorbed surface for them and secreting anabolic substances for osteoblast differentiation and activation. For this reason we used human mesenchymal stem cells for culture in the membrane scaffolds inducing the differentiation in osteoblasts and human monocytes to trigger osteoclastogenesis. Osteoclastic resorption of the scaffold material would lead to subsequent induction of osteoblasts and faster bone formation with mesenchymal stem cells. Our results show that osteoblasts and osteoclasts were successfully differentiated in the developed PCL-HA membrane scaffold. This membrane system will lead to insights in the creation of a controllable osteoinductive microenvironment based on the specific properties (e.g. basic composition, surface chemistry, architecture) and on the function (resorption coupled to proliferation and differentiation) of defined cellular systems. Acknowledgments The authors acknowledge Italian Ministry for University and Research, MIUR, for funding MATERA ERANET Project “Scaffolds for Tissue Engineering - SCATE BHH-2177”.

Membranes made of biodegradable polymers with high mechanical strength, flexibility and optical transparency, optimal degradation properties and biocompatibility are critical to the success of tissue engineered devices and drug delivery systems. In this work, a prototype implantable medical device fabricated from elastomeric scaffolds with tunable degradation properties is being developed for long-term drug delivery applications. Most biodegradable polymers suffer from short half life resulting from rapid and poorly controlled degradation upon implantation, exceedingly high stiffness, and limited compatibility with chemical functionalization. Here we report an implantable drug delivery devices constructed from a recently developed class of biodegradable elastomeric poly(ester amide)s, poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)s (APS), showing a much longer and highly tunable in vivo degradation half-life comparing to many other commonly used biodegradable polymers with a triggered degradation mechanism. The device has been tested for degradation rate and drug permeation properties in order to predict performance in the implantation environment. This device is fully biodegradable; the fabrication process is fast, inexpensive, reproducible, and scalable, making the approach ideal for both rapid prototyping and manufacturing of tissue engineering scaffolds and drug delivery devices.

Polymer membranes are critically important in addressing urgent global needs in the 21st century for reliable, sustainable, efficient access to clean energy and clean water. Polymer membranes have emerged as a leading technology to desalination water (reverse osmosis and nanofiltration) and are being explored for energy generation in applications such as reverse electrodialysis and pressure retarded osmosis. Furthermore, efforts are under way to develop additional applications of membranes for water purification, such as forward osmosis and membrane-assisted capacitive deionization. In each of these applications, control of water and ion transport across polymer membranes is critically important for optimizing performance of such membranes. This presentation focuses on the fundamentals of ion and water transport in polymers. Structure/property correlations are shown for a variety of polymers, including uncharged and charged materials. The solution/diffusion model is described for water and ion transport. The role of free volume in governing diffusion of solutes through hydrated polymers is demonstrated. The existence of a water/salt permeability/selectivity tradeoff relation is shown for polymers being considered for such applications. Comparisons are made to similar physics governing gas transport in polymers used for gas separations applications.

RO(Reverse Osmosis) membrane technologies have made great progress in last 50 years. In water desalination field, both energy saving and water quality improvement have been two major subjects. High-performanced membranes are still demanded to achieve lower cost, lower energy consumption and higher water quality. Fundamental research for RO membranes has been made through investigating physical and chemical properties based on PALS(Positron annihilation lifetime spectroscopy) study , computer chemistry and TEM (Transmission electron microscopy) analysis, which has resulted in the advanced RO membranes with high flux, high rejection, excellent chemical durability. Pore size analyses for separating functional layer in composite sea water RO membranes were conducted with PALS study, and membranes showed pore sizes in the range of 5.6 - 7.0 Å. Furthermore, the correlation between pore size of RO membrane and boron permeability was revealed. In addition, the molecular dynamics simulations, based on the chemical structures established by 13C NMR study and the estimated amount of water, were performed. In order to determine pore sizes in the polymer models, the connolly surface calculations were performed to water-deleted optimized polymer models. The calculation results showed that the pore sizes were estimated as 6 - 8 Å, which were well agreed with those of measured from PALS analyses. The comparison between pore size of RO membrane and typical removal substances, such as boric acid and sodium ion, were conducted by calculation with considering their hydrated state. Sodium ion was strongly hydrated, however, boric acid was hardly hydrated in neutral pH region. Consequently, the pore size of RO membrane was almost same as a hydrated sodium ion, but was a little larger than a non-hydrated boric acid. It was considered that it's reason why permeability of boron is larger than that of NaCl. Only a little difference in the size between pore and substances, including the difference between hydrated states, must dominate the removal performance. The structural analysis with TEM through a special treatment of membrane for preserving the structure gave precise image of cross section of protuberance, and it enabled a quantification of surface morphology. According to the precise image, since the inside of protuberance was proved as a cave-like structure, the contribution of this structure to water permeability was agreeable. With the comparison between membranes having different water permeability, larger membrane surface area or thinner membrane thickness showed higher water permeability. Consequently, the correlation between the morphology of protuberance and water permeability of membrane was revealed. Moreover, RO membranes with higher durability were developed through polymer structure analysis based on thermodynamics.

Engineered osmosis (EO) is a platform technology that relies on osmotic flow induced by concentration differences across a selective membrane to purify water, dewater solutions and generate electricity. EO encompasses a suite of technologies. Forward osmosis (FO) has recently been considered for seawater desalination, wastewater reuse, and food processing and is considered a low cost alternative to reverse osmosis (RO) and evaporative approaches. Direct osmotic concentration (DOC) is an emerging method to gently dewater aqueous solutions without the use of heat or high pressure. Pressure retarded osmosis (PRO) has been considered for harvesting osmotic potential at river deltas and within “osmotic engine” systems to generate electricity with a hydroturbine. Any EO technology requires a tailored membrane that not only is highly selective, but also exhibits properties that promote osmotic flow. Available desalting membranes are primarily designed for RO and have in previous studies exhibited poor flux and salt rejection performance when used in FO. This reduction in performance is attributed to mass transfer resistances present within the porous support layers that are ubiquitous for these membranes. While these layers provide little resistance to hydraulic flow in RO, they dramatically impact mass transfer in forward osmosis, causing what is commonly referred to as internal concentration polarization. New membrane have been developed at the University of Connecticut which dramatically reduce this mass transfer resistance by chemically and structurally changing these support layers. New thin film composite (TFC) membranes have been developed that exhibit similar selectivity to RO membranes while employing thin, porous and hydrophilic support layers. We take 3 approaches when developing these membranes. Our simplest approach is to modify existing RO membranes to have hydrophilic support layers using polydopamine. This modification technique has yielded am 8-12 fold increase in osmotic water flux when compared to unmodified membranes and matched performance with today&’s commercially available FO membrane from Hydration Technology Innovations (HTI). Our next approach is to use an intrinsically hydrophilic microporous membrane as a support for a thin film composite membrane. This project, still in its infancy, has yielded a membrane with a 50-100% better water flux with a dramatically decreased salt flux when compared to the HTI membrane. Our third approach has been to completely re-design of the membrane. By employing an electrospun nanofiber nonwoven as a support, we have fabricated a new type of TFC membrane that is exceedingly thin (approximately 10 microns). Its performance is 200-400% better than today&’s commercial FO membrane. In all, these three approaches, or the combination thereof, may yield a next generation membrane that will ultimately enable EO technologies.

Fast and low cost water sterilization is a hot topic. Thereby, a big advantage would be to not only separate microorganism (e.g. bacteria) from the water but also to prevent further growth of contaminated bacteria after water treatment. This novel twofold sterilization method would provide a secure strategy to sterilize water. Since phosphate is essential for growth in all organisms and serves as a main building block for nucleic acids, proteins and energy carriers, the lack of phosphate can prevent bacteria from growth. Lanthanum is known to bind very strongly to phosphate and is already used for phosphate reduction in open water and to reduce algae overgrowth or for medical purposes, in the form of lanthanum carbonate, to reduce excess of phosphate in the human body. Recently, we showed that lanthanum oxide nanoparticles are able to bind phosphate and can therefore be used to prevent bacteria and algae growth in water [1]. In the present work we produced a polymer membrane with incorporated lanthanum oxide nanoparticles by a novel nanoparticle assisted process recently developed in our labs [2], in which water soluble particles were used as templates. This low cost method opens a new possibility to remove phosphate quickly and easy by filtration and further prevents bacteria growth in the filtrated water. [1] L.C. Gerber, N. Moser, N.A. Luechinger, W.J. Stark, R.N. Grass, Phosphate starvation as an antimicrobial strategy: the controllable toxicity of lanthanum oxide nanoparticles, Chem. Commun., 48, 3869-3871 (2012). [2] C.R. Kellenberger, N.A. Luechinger, A. Lamprou, M. Rossier, R.N. Grass, W.J. Stark, Soluble nanoparticles as removable pore templates for the preparation of polymer ultrafiltration membranes, J. Membr. Sci., 387, 76-82 (2012).

Oil and water separation is an extremely costly problem in the petroleum industry. Pumping the complete emulsion to the surface requires substantially more power than pumping the oil alone. A membrane that can efficiently separate oil from water at the source would revolutionize this process. To this end a novel, layered, hierarchical thermoplastic membrane was fabricated with both nanoscale and microscale features. Modifying the length scales involved in fabrication of the membrane yields interesting and non-obvious implications. Taking it a step further, chemical treatments have been used to achieve higher hydrophobicity for the membrane by lowering the surface energy of the membrane surface. Although this research focuses on oil-water separation, the results have implications for other multiphase systems and hold for many other filtration and separation technologies including in lab-on-chip devices and micro/nanofluidic devices.

Self-assembly of di- and triblock copolymers is a powerful method for manufacturing highly ordered structures with nano-sized patterns. Films with regular monodisperse nanopores and ultrahigh porosity are needed in applications, which vary from water purification, sensors, information storage, as templates for nanowires, scaffolds for tissue engineering and controlled drug delivery. Block copolymer self-assembly has been proposed as formation method for artificial highly selective membranes since many years. This presentation will review the recent progress in this field. Fascinating membrane structures could be manufactured, but the techniques applied were in many cases time consuming and complicated. Till today an up-scaling of the self-assembly process for membrane manufacturing was not possible. The combination of the most common membrane formation process (non-solvent induced phase separation, NIPS) with block copolymer self-assembly was first described in 2007 /1/. But the mechanism was not well understood and the reproducibility with other polymers was not sufficient. We showed later that micelle formation in the membrane casting solution was the key to a successful asymmetric membrane formation /2,3,4/. We could show, that a substantial part of the self-assembly process takes already place in the concentrated polymer solution. The labile micelle assembly in solution is frozen by the non-solvent induced phase separation. This process takes place within a few seconds and is therefore very suitable for a fast membrane production. The resulting asymmetric membranes with a 100 to 400 nm thin well-ordered nano-porous top layer have an extremely high water flux due to the high pore density (higher than any other membrane with comparable pore size). The critical steps for the NIPS assisted self-assembly from very small laboratory scale to membrane manufacturing on a continuously operating casting machine will be described. /1/K.-V. Peinemann et al., Asymmetric Superstructure in a Block Copolymer via Phase Separation, Nature Materials 2007, 6(12) 992 /2 /S. Nunes et al., Ultraporous Films with Uniform Nanochannels by Block Coppolymer Micelles Assembly, Macromolecules 2010, 43, 8079 /3/ Nunes et al., Switchable pH-Responsive Polymeric Membranes Prepared via Block Copolymer Micelle Assembly, ACS Nano 2011, 5, 3516 /4/ Nunes et al., From Micelle Supramolecular Assemblies in Selective Solvents to Isoporous Membranes, Langmuir 2011, 27, 10184

By tailoring the cavity size as well as distribution, we have paid attention to thermally rearranged polybenzoxazoles(TR-PBOs) membrane material. We studied TR-PBOs membrane tuned for H2/CO2 separation via cyclodehydration of poly(o-hydroxylamide)s (PHAs) by in-situ thermal treatment. These TR-PBOs are better at pre-combustion operation because their cavity size is less than 3.5 Å so that they can separate small molecules such as hydrogen. Moreover, these materials are optimized at high temperature condition owing to decrease in CO2 solubility compared to that of H2 at that condition. As temperature increased, the gas permeability increased but the permeability difference between hydrogen and carbon dioxide was much larger than that at the ambient temperature. Especially we can also tell this phenomena by focusing on the novel relationship between operating temperature and cavity size and distribution, meaning that these TR-PBOs can be very high potential for some separation field such as IGCC(Intergrated Gasfication Combined Cycle) regarding as very harsh temperature and pressure condition. In the present study, we will report on the synthesis of various TR-PBOs from dehydration, characterization analysis about them including positron annihilation lifetime spectroscopy (PALS), and the tendency between cavity size and distribution and gas transport properties according to various structures.

Chemical and nanomaterial contaminants from various commercial products reach the environment through the improper disposal of waste materials. Recent results from our lab indicate that many of these nanoparticles are toxic to living systems. This prompted us to think of new ways to remove such toxic pollutants from water supply. In our study, a series of materials were designed and used for the removal of pollutants such as nanoparticles and dissolved organics from water. The polyvinyl alcohol nanofibers were prepared by electrospinning technique and surface functionalized with different functional groups. In another approach, the natural nanofibers were isolated from natural sources and used as such or coated with chitosan onto the surface of the fiber. Scanning electron microscope images revealed that the PVA nanofibers were of 200 - 300 nm and the isolated cellulose nanofibers were 30 - 40 nm in diameter. Carbon nanomaterials were also prepared and used for removal of pollutants. The designed materials showed high filtration efficiency for removal of dissolved pollutants from water. Such readily available and cost effective materials may find potential applications in water purification and conservation. Acknowledgement: The authors thank the Environment and Water Industry Programme Office (EWI) under the National Research Foundation of Singapore (PUBPP 21100/36/2, NUS WBS no. R-706-002-013-290, R-143-000-458-750, R-143-000-458-731) for the financial support of the work.

Polymeric separation membranes are used in a broad range of industrial applications for producing commodities (e.g., water and energy carriers); specialty products (e.g., biologicals and pharmaceuticals); and high value items (e.g., ultrapure gases and liquids for semiconductor manufacturing). Novel membranes are actively pursued for improving separation characteristics, reducing energy costs, and being more environmental friendly. Fouling is a detrimental phenomenon that prevails in all membrane processes, as the retained components ranging from particles, biological species to organic materials gradually deposit onto the surface of the membranes and eventually may be strongly adhered and difficult to clean off. Fouling inevitably lowers the membrane's performance and must be accounted for through increased capital and operating costs. Many approaches have been investigated to increase the fouling resistance of membranes, including chemical modification of the surfaces, addition of nanoparticles, and process design, to name a few. All of these approaches enjoy varying degrees of application-specific success, but can be improved upon. Here, we describe a novel approach to improve the fouling resistance of the polymeric membranes by micro and nano-texturing the surface of the membrane. By controlling the lithographic processing conditions, sub-micron anisotropic surface patterns were successfully imprinted onto a commercial ultrafiltration membrane, without sacrificing the separation and permeance figures-of-merit. Model suspensions (containing either colloidal particles or proteins) were filtered using patterned and non-patterned (control) membranes. For both types of suspensions, significant improvements in the overall filtration productivity and regeneration ability were found for the patterned membrane, revealing appreciable reduction in both surface deposition rates and adsorption by particles and proteins. This new approach does not involve any chemical modifications and can be applied to a range of synthetic membranes and can be straightforwardly translated to industrial membrane manufacturing processes. In addition, it holds the promise of being a method that will be application-agnostic in terms of its usefulness.

Mixed matrix membrane (MMM) is a relatively new type of membrane material with good selectivity, permeability, mechanical strength, thermal and chemical stability as well as processibility. This research work focuses on creating a membrane that is similar in principle to the MMM; a membrane of inorganic particles homogeneously distributed in a partially carbonized-polymer phase, viz. a carbonaceous matrix, but bypassing the complex experimental procedure of the casting evaporation method which is commonly used for the fabrication of MMM by employing a dry-mix method. Currently, the main difficulty in preparation of shape-selective Al-rich zeolite membranes (e.g. LTA or FAU) for gas separation is their strongly negative electric surface charge as found by zeta potential measurements. The extreme mismatches in thermal expansion coefficients between the zeolite layer and support layers also causes damage and surface flaws [1]. Two tactics have been developed to close down pin holes and gaps formed due to partial decomposition of the polymer phase during the partial carbonization phase. The results obtained thus far show that this is a promising method of producing a mixed matrix membrane in a simpler and more direct manner with an even higher zeolite loading (up to 75% loading) than conventional mixed matrix membranes (~50%) due to agglomeration issues [2]. Our novel method would bypass the tedious conventional cast evaporation fabrication methods and yet achieve comparable or even better separation results. Furthermore, the carbonaceous matrix would not only promote better interaction with the inorganic phase, further modifications can be made to it as some pendant groups still remain attached to it as it is not fully carbonized. The details of the experiments done and method of synthesis of the membrane would be elaborated in the presentation. References: 1. Caro, J., D. Albrecht, and M. Noack, Why is it so extremely difficult to prepare shape-selective Al-rich zeolite membranes like LTA and FAU for gas separation? Separation and Purification Technology, 2009. 66(1): p. 143-147. 2. Garcia, M.G., J. Marchese, and N.A. Ochoa, Effect of the Particle Size and Particle Agglomeration on Composite Membrane Performance. Journal of Applied Polymer Science, 2010. 118(4): p. 2417-2424.

Membrane-based gas separations are very attractive as alternatives to conventional energy intensive processes such distillations and adsorption-based separations. However, membrane-based gas separations occupy only a small fraction of current gas separation markets. This is mainly due to the limitations of polymeric membranes. In this talk, I would like to discuss alternative membrane materials and concepts that can overcome some of the limitations of polymer membranes. Nanoporous framework materials such as zeolites and metal-organic frameworks hold great potentials as new membrane materials due to their well-defined pores in the scale of molecules. I will give examples of these membranes, in particular, metal-organic framework membranes, exhibiting outstanding performances for commercially-important challenging separations such as olefin/paraffin separations. Besides, some of these new materials give unprecedented opportunities in designing membrane modules and manufacturing membranes in commercially viable manner.

Ultrananocrystalline Diamond (UNCD) is a promising material for biomedical applications, due to its extraordinary mulifunctionality, including tunable electrical conductivity, extremely low wear, very low coefficient of friction, high smoothness, bio-inertness and biocompatibility. UNCD is exceptional for implantable medical devices requiring stringent biological performance. Drug delivery systems are important medical devices providing significant medical (improve pharmacokinetics decreasing drug dose and toxicity) and commercial (increasing product portfolio by adding new products and decreasing drug discovery costs by recycling old drugs) advantages. This presentation will focus on the design, fabrication and characterization of UNCD membranes for passive and active drug delivery devices. UNCD membranes were fabricated in a clean room facility using thin film deposition and microfabrication techniques, including: 1) UNCD thin film growth by microwave plasma chemical vapor deposition (MPCVD) on a Si substrate after a nanodiamond seeding process on the silicon surface, 2) photolithography using a specially designed mask to define a window on the backside of the wafer, 3) reactive ion etching (RIE) to pattern the Si3N4 mask for the cavity sustaining the UNCD membrane on the backside of the wafer, and 4) wet chemical etching to create the cavity sustaining the UNCD membrane. Square membranes of 200-1000 µm in size with a thickness ranging between 100-500 nm were fabricated and characterized by Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM) and reflectometry. Fabrication of passive drug delivery devices was done using the focused ion beam (FIB) technique to produce holes with micron size dimensions in the UNCD membranes to enable controlled drug diffusion through the latter. For the active drug delivery device, based on a piezoelectrically actuated valve, a Pt/piezoelectric AlN/Pt layer heterostructure was grown and patterned on the UNCD membrane with a Ti adhesion layer, followed by FIB etching to define the valve aperture. By applying voltages between the top and bottom Pt electrodes layers the piezoelectric AlN layer is actuated allowing opening and closing the valve. Work in progress will be described, showing the optimization of AlN film growth and integration with UNCD membranes and development of fabrication processes to produce piezoelectrically actuated valves. PDMS was used to seal the bottom face of the Si substrate, where the integrated UNCD membrane/cavity structure was fabricated, to create the reservoirs. Work in progress to optimize and test active and passive drug delivery devices based on UNCD membranes will be discussed in the presentation. Work supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences-Materials Science, under contract DE-AC02-06CH11357.

The recently-reported exceptionally-fast fluid transport rates in carbon nanotube (CNT) pores of a few nanometer diameters [1] spurred great interest for their application as nanofluidic channels in several areas ranging from desalination and carbon capture, to drug delivery, protein separation and breathable fabrics. For these applications, a fundamental understanding of the selectivity of these pores for specific molecules is needed and, unfortunately, still lacking. Also, robust strategies to precisely control the transport selectivity of CNTs are required. Here, we demonstrate that atomic layer deposition (ALD) of alumina is able to reversibly tune the transport selectivity of CNT pores for small ions without loss of their unique ultrafast fluid transport properties. On the contrary, previous functionalization strategies reported in the literature resulted in a two orders of magnitude flow-rate reduction. For our studies, we used a silicon nitride membrane with well-aligned, sub 2-nm carbon nanotubes as only through-pores [1]. Pressure-driven filtration of small ions before and after ALD functionalization is investigated as a function of solution pH. Our results show that, for a sufficiently large number of ALD cycles, sulfate ions are almost completely rejected by Al2O3 modified CNT pores when solution pH is above alumina pKa, whereas unmodified CNTs partially reject these anions for pHs greater than the pKa of carboxylic groups [2-3]. For low ALD cycle numbers, the coexistence of carboxylic groups and aluminum oxide functional groups dictate the ion selectivity of the membrane platform. Finally, at very low pHs, the CNT pore selectivity appears to be governed by size exclusion. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [1] Holt J., Park H.G., Wang Y., Stadermann M., Artyukhin A.B., Grigoropoulos C.P., Noy A. and Bakajin O., “Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes,” Science, 312: 1034 (2006) [2] Fornasiero F., Park H.G., Holt J.K., Stadermann M., Grigoropoulos C.P., Noy A., Bakajin O., “Ion Exclusion by sub 2-nm Carbon Nanotube Pores”, PNAS, 105 (45):17250-117255 (2008) [3] Fornasiero F. , In J.B., Kim S., Park H.G., Wang Y., Grigoropoulos C.P., Noy A., Bakajin O., “pH-Tunable Ion Selectivity in Carbon Nanotube Pores,” Langmuir, 26 (18): 14848-14853 (2010)

Graphene, and related materials, such as graphene oxide (GO) and reduced graphene oxide (RGO) are unique one-atom thick membrane materials with applications in photovoltaic energy conversion. Both graphene and GO membranes are impervious to gas molecules as small as He [1, 2]. Chemical treatments such as reduction allow tunability of graphene&’s permeability. Nair and colleagues recently reported permselective transport strongly favoring water vapor over inert gases through submicrometer-thick GO films; these multilayer GO films are 100 times more permeable to water vapor than similar RGO films [2]. We present a tunable assembly technique for deposition of GO and RGO monolayers on arbitrary substrates and comparisons of the permeability of these films. Langmuir-Blodgett deposition was used to assemble GO membranes on commercial porous alumina supports. Lower initial GO concentrations (~0.2 mg/mL in water) yielded the greatest surface coverage, as confirmed by SEM micrographs of GO films on both alumina and silicon. Such SEMs revealed that overlapping GO films can trap water bubbles for weeks, demonstrating GO&’s membrane potential as a water barrier. To promote a smooth, rather than wrinkled, overlap of adjacent sheets, the subphase&’s pH was increased, thus deprotonating the GO and allowing water molecules to lubricate the sheets during compression. To open nanopores in the GO, GO was reduced using ascorbic acid, thereby removing oxygen functional groups from the basal plane. UV-Vis spectroscopy confirmed that RGO was formed. SEM micrographs of GO and RGO on porous alumina showed conformed to and smoothly covered the dimpled alumina. We compare gas transfer rates for inert and reactive gas species through these GO and RGO membranes and discuss the impact of graphene source (GO versus RGO) and fabrication techniques on the permeability of these membranes. One application for RGO membranes is as a transparent conductive electrode for organic photovoltaics. In order to minimize the degradation of their organic constituents, organic photovoltaics require conductive membranes impervious to oxygen and water vapor. While water-impervious RGO membranes are a promising material for photovoltaics, other energy applications for graphene membranes are also envisioned. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC0494AL85000. [1] Bunch et al., Nano Lett. 8, 2458-62 (2008). [2] Nair et al., Science 355, 442-4 (2012).

Directed mesochannel alignment has long been a challenging task in forming periodic mesoporous silica (PMS) membranes. While a vertical alignment of mesochannels against the supporting substrate is a prerequisite to meeting various industrial needs such as separation, filtration, sensing, membrane reaction and so forth, mesochannels of PMS membrane tend to be oriented parallel respective to the substrate surface in many cases [1, 2]. Till recently, efforts on vertical alignment of mesochannels toward a substrate were limited to several methods including such as surface energy control, confined space (AOA pores) utilization, action of external (electric or maganetic) fields, which, however, are far from satisfaction. Graphene is a group of new nanomaterial which is attracting explosive interests due to their extraordinary properties in electric and thermal conductivities, mechanical stiffness, and chemical sensing sensitivity. Recently, we succeeded in obtaining a cutting-edge nanocomposite structure in which the layers of reduced graphene oxide (rGO) are sandwiched by PMS films with their mesochannels perpendicularly aligned toward rGO layers [3]. Possible synthesis of these new materials carves out a new opportunity for high performance achievement in energy, environment, and medicine applications, for example, molecular sieve sensing, DDS, electrical capacitor, high density memory devices, and so forth. In this presentation, we&’ll review these unusual nanocomposites and report the nearest recent progress regarding their synthesis, structures, and functionalities. [1] H. Yang, H.; Kuperman, A.; Coombs, N.; Mamiche-Afara, S.;Ozin, G. A. Nature 1996, 379, 703. [2] I. A. Aksay, et al. Science, 1996, 273, 892. [3] Z. -M. Wang et al. ACS Nano, 2010, 4 (12), 7437.

Unprecedented thin-film composite (TFC) membranes with 3D-interconnected, molecular-size ionic pores have been prepared using a new gemini imidazolium lyotropic (i.e., surfactant) liquid crystal (LLC) monomer system that forms a type I bicontinuous cubic (Q_I) LLC phase with glycerol. The larger, softer, cationic imidazolium headgroups on this new LLC monomer allow for Q_I phase formation with several polar organic solvents such as glycerol, instead of just pure water. The use of a high boiling organic solvent such as glycerol in place of water for Q_I phase formation now allows facile solution-based thin film processing using traditional low-boiling casting solvents such as MeOH, to give initial TFC membranes with a le;3 µm thick active separation layer on top of porous poly(ether sulfone) supports. The resulting cross-linked Q_I TFC membranes have uniform, 0.96-nm-wide, annular nanopores that perform size sieving of neutral solute molecules from water. They were also found to reject smaller hydrated salt ions near or at the high level of commercial reverse osmosis (RO) membranes due to additional ionic pore-metal salt cationic repulsive interactions. This new material also has very good water flux at 400 psi filtration pressure and a thickness-normalized water permeability comparable to the active layer material in current TFC RO membranes. The design, synthesis, processing, and water nanofiltration/desalination performance of this new type of nanoporous polymer membrane will be presented. In addition, some strategies for adjusting nanopore size in this new membrane material will also be presented.

A route has been developed for synthesis of a novel form of Nanoscale Alumina Fibre (NAF). The individual fibres are ~7-10 nm in diameter, with lengths up to 8 cm. A mat or sheet is produced, grown from a metallic aluminium precursor in the form of a melt. The fibres are aligned in the through-thickness direction of the sheet, occupying about 5% of the space. The product can be manufactured relatively quickly, and in large quantities - ie at kg hr^-1 rates. This is probably associated with the fact that all of the relevant transport phenomena take place through liquid and solid phases, and not through any gaseous phases. In the as-produced form, the crystal structure of the fibres is predominantly γ-Al₂O₃, although they transform to α-Al₂O₃ on exposure to temperatures above about 1300 ^omicron;C. The very fine diameter of these fibres, combined with their excellent stability at high temperature, clearly offers potential for the development of applications such as catalysis substrates, filters, high temperature insulation [1] etc. Previous work in the group has demonstrated that NAF membranes, produced by sedimentation from suspension in liquid and exhibiting an approximately planar random orientation distribution, could successfully be used to filter (relatively small molecular weight) synthetic dyes [2]. In the current work, it is shown that the uniaxial orientation distribution of the NAF can be retained in a durable membrane, with the volume fraction being increased from 5% to 26 - 43%. The final volume fraction is dependent on the initial fibre diameter. These are termed NanoPillar membranes (NPM), to distinguish them from the previously-produced planar random NAF membranes. The NanoPillar membranes (NPM) have been characterised using SEM, AFM, BJH and mercury porosimetry. They are robust and have good handling strength. A set-up has been created to study transport phenomena through these membranes. This study has included investigation of the Exclusion-Enrichment Effect (EEE), arising as a result of the electrical double layer (EDL) on alumina surfaces, where the fixed surface charges are compensated by mobile counter-ions in solution. Work will also be presented on mechanical, permeation and filtration characteristics of the NPMs. References [1] Clyne, TW, Golosnoy, IO, Tan, JC and Markaki, AE, Porous Materials for Thermal Management under Extreme Conditions, Phil. Trans. Roy. Soc. A: Mathematical, Physical & Eng. Sciences, vol.364 (2006) p.125-146. [2] Su, VMT, Terehov, M, Clyne, TW, Filtration Performance of Membranes Produced Using Nanoscale Alumina Fibres, Adv. Eng. Mater., (2012) accepted for publication.

There are growing demands to fabricate polymeric thin films with vertically aligned sub-nanometer channels for applications including carbon capture, gas separation, water desalination, batteries, fuel cell membranes, and solar-fuel conversion. Generating membranes with molecular level control over the pore size, shape and surface chemistry is a critical bottleneck, and has been investigated across many disciplines. We developed a new approach where the growth of cyclic peptide nanotubes can be directed in a structural framework afforded by the self-assembly of block copolymers. This new strategy circumvents impediments associated with aligning and organizing high aspect ratio nano-objects normal to the surface. We successfully fabricated sub-nanometer (~0.7 nm) porous membranes containing high-density arrays of through channels on flexible substrates. Transport studies showed that the sub-nanometer porous membranes have size-selective separation and enhanced mass transport. Fundamentally, the hierarchical co-assembly strategy described demonstrates the feasibility of synchronizing multiple self-assembly processes to achieve hierarchically structured soft materials with molecular level control. In parallel, we focus on synthesizing cyclic nanotubes with molecularly defined size, shape and interior chemistry to control selectivity. By incorporating 3-amino-2-methylbenzoic acid in the D, L-alternating primary sequence of a cyclic peptide, we developed a facile route to present functional group in the interior of the nanotubes without compromising the formation of high aspect ratio nanotubes. The new design of such a cyclic peptide also enables us to modulate the nanotube growth process to be compatible with the polymer processing window without compromising formation of high aspect ratio nanotubes, thus opening a viable approach toward molecularly defined porous membranes.

This paper briefly describes recent progress in the development of microporous amorphous silica-based membranes for hydrogen separation. Synthetic methods using various metal-organic precursors, chemical compositions, related nanostructures and gas permeation properties of the amorphous silica-based membranes will be summarized and shown. Then, our recent study of novel amorphous silica-based composite membranes with multi component [Si-M1-M2-O, (M1, M2= hetero element)] system will be shown and discussed. The amorphous silica-based multi component membrane has been synthesized by dip-coating of homogeneous metal-organic precursor solution on a fine porous alumina support followed by the subsequent heat treatment at 873 K in air. The gas permeation properties of the membrane was found to depend strongly on the chemical composition of the Si-M1-M2-O membrane material system, and some transition metal cation-doped membranes exhibited a unique high-temperature H2 permeation behavior which was apparently different from that explained by the activated diffusion often observed for the metal-organic precursors-derived microporous amorphous silica membranes. To clarify the dominant mechanism for the H2 permeation, powdered samples were prepared using the same metal-organic precursor solution for membrane syntheses, then characterized by the X-ray diffraction (XRD), FT-IR measurement by using DRIFTS technique and the TPR/TPD analysis. From the results of these analyses, the reactivity toward hydrogen at high temperature was found to be significantly higher than that of dopant-free amorphous silica and these experimental results will be discussed from a viewpoint of application of the ceramic membranes for developing novel highly efficient hydrogen production, storage and transportation systems.

Pd-based hydrogen selective membranes performance can be affected by the gas components of a hydrogen containing mixture. In a hydrogen production process from natural gas, methane is converted into a mixture of CO2, CH4, CO, H2, H2O and inert gases, which can inhibit or even poison the membranes surface. Especially polluting compounds like H2S are very common in process streams derived from natural gas or oil refinery industry. Some studies have shown that Pd-alloy membranes have a better H2S resistance than the Pd ones. A PdCu membrane was prepared by electroless plating and tested in different conditions. H2S addition effect was analyze in two ways: (I) in a H2:H2S atmosphere, (II) in a complex mixture produced in a catalytic reactor from methane with H2S addition. The membrane operated for longer than 50 hours under variable composition complex mixtures with a H2 percentage between 27 and 34%. Between 60 and 70 % of the hydrogen fed to the membrane was recovered in the membrane module, regardless of the composition. In the first tests with H2S addition in H2:H2S mixtures, it was observed that sulfur negative effect was reversible. Hydrogen flow through the membrane decreased by around a 75% when H2S was added, but it went back to the previous values when removing it from the system. However, sulfur was found to attack weak areas like grain boundaries. When taking out the membrane from the module a crack was observed in the membrane area that had operated at the highest sulfur concentration. When analyzing the used membrane with SEM, rough surface was detected. The crystalline structure of the PdCu had not changed during the tests and it seemed that the Cu atoms were located inside the Pd crystalline net. Adsorbed sulfur was not detected by EDX, XRD or XPS.

Oxygen transport membranes (OTM) developed by Praxair have been fabricated and tested at 800-1000°C in an experimental coal gasifier using Utah PRB and Illinois coal blends. Oxygen flux was measured and found stable over approximately 100 hours of gasifier operation. Study of interactions between the OTM and coal ash and gas phase impurities indicated that the OTM components remain stable against coal ash and do not show any indication of solid or liquid (slagging) compound formation. The structure of the active layer exposed to the coal gas also remains stable and interactions with sulphur were not observed. Experimental results will be presented. Thermochemical analysis of the solid-solid and solid-gas interactions will be described.

The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H2 can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single-step under high temperature conditions. Polymer-derived porous and amorphous silicon-based ceramics are candidate materials for membrane applications, in particular due to their extraordinary high temperature stability with respect to phase separation, crystallization and corrosion phenomena. For example, three times Si-B-C-N coated multilayer membranes based on Si-B-C-N/γ-Al2O3/α-Al2O3 systems show higher H2/CO permselectivities of about 10.5 and a H2 permeance of about 1.0 x 10-8 mol m-2 s-1Pa-1. If compared to the state of the art of microporous membranes, multilayer Si-B-C-N/γ-Al2O3/α-Al2O3 membranes are appeared to be interesting devices for hydrogen separation because of their tunable nature and high-temperature and high-pressure stability. References: 1. Ravi Mohan Prasad, Yuji Iwamoto, Ralf Riedel and Aleksander Gurlo, “Multilayer amorphous-Si-B-C-N / γ-Al2O3 / α-Al2O3 membranes for hydrogen purification”, Adv. Eng. Mater. 12 (2010) 522-528. 2. Ravi Mohan Prasad, Aleksander Gurlo, Ralf Riedel "Microporous ceramic coated SnO2 sensors for hydrogen and carbon monoxide sensing in harsh reducing conditions“, Sensors & Actuators: B. Chemical 149 (2010) 105-109. 3. Mahdi Bazarjani Seifollahi, Hans-Joachim Kleebe; Mathis Müller, Claudia Fasel, Yazdi Mehrdad Baghaie, Aleksander Gurlo, Ralf Riedel, "Nanoporous Silicon Oxycarbonitride Ceramics Derived from Polysilazanes in-Situ Modified with Nickel Nanoparticles", Chemistry of Materials 23 (2011) 4112-4123. 4. Ravi Mohan Prasad, Gabriela Mera, Koji Morita, Mathis Müller, Hans-Joachim Kleebe, Aleksander Gurlo, Claudia Fasel, Ralf Riedel, “Thermal decomposition of carbon-rich polymer-derived silicon carbonitrides leading to ceramics with high specific surface area and tunable micro- and mesoporosity”, J. Europ. Ceram. Soc. 32 (2012) 477-484.

We will describe the preparation and study of a new class of proton-conducting membrane materials, namely, nanoporous colloidal membranes whose proton conductivity results from the nanopore surface modification with polysulfonic acid brushes. Our design has a number of unique features that are fundamentally different from the traditional polyelectrolyte or composite organic-inorganic membranes. In it, the highly ordered silica colloidal crystal with the continuous network of nanopores serves as a matrix providing mechanical stability and water retention and supporting the proton-conducting polymers, therefore eliminating the need to optimize simultaneously the mechanical and proton-conducting properties of the polymer. The inorganic matrix also allows achieving high degrees of acid functionalization of the polymer without the danger for the membrane to become water soluble, and maintaining mechanical stability under the oxidative conditions and high temperature. We prepared sintered self-assembled nanoporous silica colloidal crystals modified with poly(3-sulfopropylmethacrylate), pSPM, and poly(stryrenesulfonic acid), pSSA, brushes covalently attached to the nanopore surface. The resulting robust membranes possess temperature and humidity-dependent proton conductivity of ~2 × 10^-2 S cm^-1 at 30 °C and 94% R.H., ~1 × 10^-2 S cm^-1 at 85 °C and 60% R.H., and water uptake of ca. 20 wt% at room temperature. We also studied the proton conductivity of the membranes containing co-pSPM/poly(2-ethoxyethylmethacrylate) brushes as a function of sulfonic acid content, and measured the open circuit potential (OCP) of model fuel cells containing these membranes. In both cases, we found an S-shaped dependence of conductivity and OCP on the amount of sulfonated monomer in the polymer brush.

The global needs of new polymeric materials that can fulfill the requirements of the innovative technologies e.g. fuel cell, flow battery and water desalination is nowadays essential. Herein we present such a polymer which is based on a well known structure of polystyrene and possessing simultaneously excellent ion-conductive properties and high resistance to thermal and oxidative treatments. Highly sulfonated poly(pentafluorostyrene) (sPFS) is obtained in three steps: (i) emulsion polymerization of the pentafluorostyrene, (ii) thiolation with metal sulfide and (iii) oxidation of the thiol-functions to the corresponding sulfonic acids. The advantages of the radical polymerization in emulsion in compare to commonly used polycondensation reaction, lie in the higher molecular weights (1000 - 100 kDa), the milder conditions (T = 90 °C in water) and the shorter reaction time (1-2 hrs). Structural analysis of sPFS confirmed a 100% sulfonation (each pentafluorostyrene unit is sulfonated), which gave us an access to polymer with extremely high ion-exchange capacity of 3.9 mequiv./g. The contrivance is in the cumulative electron withdrawing effect of the fluorine functions. This simultaneously facilitates the thiolation reaction (ii) to the level of a “click-reaction” and enhances acidity of the finally obtained sulfonic acid. Beside the high resistance to oxidative and thermal treatment (Tdecomp.= 268 °C at 70% oxyden atm.), the most important consequence is the tremendous increase of the proton-conductivity being 35 mS/cm (at 160°C, 1 atm. water vapor pressure), which is an order of magnitude higher than those of Nafion measured under the same conditions. Moreover, sPFS showed very small dependence of the ion-conductivity onto the water content, which is extremely important for the performance of the polyelectrolyte in the fuel cells above 100 °C. This makes sPFS the best ion-conducting polymer besides disulfonated polyphenylenes of Morton Litt (1) and sulfonated polysulfones of Klaus-Dieter Kreuer (2). All this makes us to believe in the very high potential of the sPFS as a polyelectrolyte for the fuel cell applications. (1) S. Granados-Focil, M. H. Litt Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2004, 49(2), 529. (2) M. Schuster, C. C. de Araujo, V. Atanasov, H. T. Andersen, K.-D. Kreuer, J. Maier Macromolecules 2009, 42, 3129.

Nafion is the industry standard proton exchange membrane (PEM) (also known as a polymer electrolyte membrane), a critical component in the conversion of chemical energy into electrical energy in H2/O2 fuel cells. It is well-known that Nafion&’s complex morphological structure comprised of hydrophilic, ionic domains dispersed in a semicrystalline, hydrophobic matrix plays an integral role in the performance properties (i.e., proton conductivity, mechanical properties, swellability, and transport). The proton conductivity in Nafion, which is critical to fuel cell performance, has been directly connected to the level of hydration of the membrane. Although significant efforts have been made in water management for optimal fuel cell performance, there is still a general lack of knowledge on the response of Nafion at interfaces and confined to very thin layers. Within the membrane electrode assembly (MEA) in a fuel cell, Nafion is heterogeneously dispersed as an ionically conductive binder and often confined to thin layers that are on the order of 2 nm to 10 nm thick.1,2 This interfacial boundary region mediates the transport of reactant gases, ions, electrons, and water, which affect the performance of the entire fuel cell. However, the structure, transport, and performance properties of Nafion thin films, where interfacial interactions dominate, are still poorly understood. A limited number of studies have demonstrated deviations in either the morphology, water (or solute) sorption or proton conductivity from their bulk values in Nafion thin films. In this presentation, we study Nafion films in the range of 20 nm to 222 nm thick on Si substrates as a model system for Nafion confined on the catalyst particles and carbon supports in the electrode layer of a MEA. The water absorption and transport kinetics are characterized as a function of relative humidity. While the humidity-dependent equilibrium swelling ratio, volumetric water fraction, and effective diffusivity are relatively constant for films thicker than ca. 60 nm, we observe measurable suppressions of these properties in films less than ca. 60 nm. Below this transition thickness, we also studied the structure by varying interfacial interations between Nafion and substrate. Water transport was found to be dependent on the interfacial structure in case of confined Nafion layers and discussed in terms of enhanced interfacial impedance. 1. More, K. L. DOE Hydrogen Program Annual Progress Report 2005, November. 2. Mashio, T.; Malek, K.; Eikerling, M.; Ohma, A.; Kanesaka, H.; Shinohara, K. Journal of Physical Chemistry C 2010, 114, (32), 13739-13745.

In this study, we investigate the nanophase-segregated structures and transport properties of quaternary ammonium grafted polysulfone membranes using molecular dynamics simulation method. For this, we develop a new force field from a reference density functional theory modeling with B3LYP and 6-31G** in order to describe the hydroxide anion. The bond stretching force constant is determined to reproduce the quantum mechanical vibrational frequency. The atomic charges are determined by Mulliken population analysis. Through the annealing procedure, the nanophase-segregated structure is developed as a function of water contents such as 10 and 20 wt %. The extent of nanophase-segregation is evaluated by the structure factor analysis, which can be compared with the experimental small angle scattering data. Once the equilibrium structures are obtained, we run long MD simulations to analyze the diffusion of water and hydroxide using the mean-square displacement analysis with an assumption of Gaussian diffusion. The nanophase-segregated structures and the transport properties will be compared to the proton exchange membrane consisting of the same polymer backbone except for the acidic functional group.

We explored here changes in the methanol permeation due to the deposition of ultrathin films of graphite oxide and graphene onto Nafion membranes. Direct Methanol Fuel Cells (DMFCs) are promising candidates to produce more clear and efficient power supplies due its high energy density, low pollution, fast recharge and room temperature operation. Therefore, fuel poisoning from methanol permeation hinders possible commercial applications of DMFCs. In this sense, the layer-by-layer (LbL) technique was exploited here to assembly different graphene supramolecular architectures onto a Nafion membrane, in order to minimize the methanol permeation. Graphite oxide (GO) was synthesized by the Hummers method and was further reduced using hydrazine in the presence of PSS, producing stable graphene aqueous suspension (GPSS), suitable for LbL applications. GO and GPSS powder samples were analyzed by FTIR and XRD, and the LbL PAH/GO and PAH/GPSS films were monitored by UV-vis spectroscopy, presenting good linear growth and adhesion, checked by repeated washings of the LbL films using ultrapure water. These graphene LbL architectures were also characterized by FTIR measurements and deposited onto a Nafion membrane, with voltammetric analysis indicating changes in the methanol permeation of the modified membranes, emphasising further application in DMFCs.

The Renewable Fuels Standard (RFS) and Energy Independence and Security Act of 2007 (EISA) mandated that 36 billion gallons of biofuels should be blended into transportation fuel by 2022. Implementing this will help reduce greenhouse gas emissions, reduce petroleum imports and encourage the development and expansion of US renewable fuels sector within rural America. Of the 36 billion gallons of biofuels, 16 billion gallons is expected to be from lignocellulosic biomass such as trees and grasses. The Black Hills of South Dakota is rich in ponderosa pine. This feedstock for bioethanol production, which is widely available due to recent pine beetle infestation, will not only add to the RFS requirement, it will also have a positive impact on rural economies in South Dakota. From the wood chips of pine, after acid pretreatment and enzymatic hydrolysis, the fermentable sugars obtained are relatively dilute in concentration (~20-30 g/L). Hence, within a biorefinery, to increase the fermentation efficiency and decrease downstream processing cost of the biofuels, concentrating the sugars can be beneficial. In this study, Reverse Osmosis (RO) and Nanofiltration (NF) membranes were tested with complex lignocellulosic hydrolysate samples for their ability to concentrate sugars prior to fermentation. Fouling analysis and membrane characterization for both RO and NF membranes were performed by SEM, AFM, BET, contact angle and FTIR spectroscopy. Efficiency of membranes for their ability to separate fermentation inhibitors (e.g., organic and mineral acids, furans and phenolic compounds) from sugars, while simultaneously concentrating the sugars was studied to make the bio-ethanol production process cost and energy efficient. In addition, molecular modeling and simulations were used as a tool to validate experimental data and to theoretically evaluate the interactions between different membrane chemistries and the components present in a lignocellulosic enzymatic hydrosylate. Molecular modeling was also used to guide the design of membrane modifications that could be used to potentially improve performance. Several commercial membranes as well as surface modified membranes produced in our labs to optimize the separation have been evaluated for throughput and purification.

In this talk, we will discuss structure, dynamics and transport of fluids in confined environments, e.g. nanopores. The interfacial structure of fluids is computed by a multiscale quasi-continuum theory. The results from quasi-continuum theory compare well with molecular dynamics (MD) and the quasi-continuum theory is several orders of magnitude faster compared to MD. The structure obtained from the multiscale theory is coupled with the particle transport equation to compute dynamics and transport in nanopores. We will discuss several applications of fluid transport through nanopores.

Grafting the ruthenium catalyst to the network of swollen chemo-responsive polymer gel creates a new class of materials, which exhibit the autonomous, coupled chemical and mechanical oscillations induced by the ongoing Belousov-Zhabotinsky (BZ) reaction. In the course of the BZ reaction, the catalyst undergoes the periodic redox variations. The mechanical oscillations occur due to the hydrating effect of the oxidized Ru that causes the gel to swell and de-swell repeatedly. The BZ gels can be used as the active medium for designing such autonomously functioning devices as micro-pumps, actuators, etc. For example, Yoshida et al. fabricated the self-driven gel conveyer from the BZ gel. Here, we present the results of computational modeling of the BZ gel-based membrane having circular perforations. Our computational approach is based on the Oregonator model for the BZ reaction kinetics, and the gel lattice spring model for the gel dynamics. First, we consider a single pore and demonstrate that both chemical and mechanical stimuli could be used to control the amplitude and frequency of oscillations of the pore size. Then, we show that introducing multiple perforations into BZ gels can drastically affect the dynamic behavior of the system. In particular, the BZ gel with two perforations can exhibit the oscillatory or non-oscillatory behavior depending on the distance between the pores. The observed effect of perforation on the BZ gel is due to accumulation of the dissolved reactants within the pores that leads (for the model parameters used) to a switching of the BZ reaction to the non-oscillatory regime. Finally, we demonstrate that the collective dynamics of pores is sensitive to macroscopic deformations of the BZ membrane.

Cyclic peptide nanotubes (CPNs) have unique chemical and mechanical features that make them squarely positioned to tackle persistent challenges in novel biomaterials, sensors, and selective membranes. These self-assembled hierarchical nanostructures are highly organized at the nanoscale and feature exceptional thermodynamical stability arising from the collective action intersubunit hydrogen bonds networks. Understanding the assembly, mechanics and transport behavior of CPNs through a multi-scale analysis is crucially important for developing science-based approaches to designing the molecular subunits and hierarchical assemblies of these materials into polymer membranes. In pursuit of addressing this need, here we report atomistic and coarse-grained simulations of cyclic peptides conjugated with polymers. Our approach involves estimation of the free energy landscape of the system along the reaction coordinate from atomistic simulation trajectories using nonequilibrium statistical thermodynamics formulations, which enables bridging scales through mapping to coarse-grain or continuum descriptions. We demonstrate the basic multi-scale approach for investigating the stability of cyclic peptide based organic nanotubes (CPNs), mapping out the elastic range of intersubunit interactions along with the large deformation and disassembly (Ruiz and Keten, Int. J. of Applied Mechanics, 2011,Journal of Engineering Mechanics, 2012). We quantify how functional chemical mutations in the interior of the nanotube as well as through conjugation onto sidechains govern assembly dynamics and selective transport. Our work illustrates the potential of atomistically informed simulations for predicting and enhancing the transport, self-assembly and mechanical behavior of peptide nanotubes simultaneously, enabling a science based approach to the synthesis of novel membranes with highly tunable properties (Hourani et al. JACS, 2011).

The goal of this work is to model the miscibility and interfacial properties of ionic liquid/polymer composites, which affect the stability and efficiency for applications like membrane gas separation, energy storage, biosensors, drug delivery, etc. For example, supported ionic liquid membranes are materials of interest for gas separations, including the separation of CO2/N2, CO2/H2, and CO2/CH4. These membranes consist of a polymer support structure that is embedded with an ionic liquid, which is a liquid salt that can be tuned to have excellent gas transport properties. The stability of this ionic liquid/polymer composite is highly dependent on the surface tension of the ionic liquid and the contact angle of the ionic liquid with the polymer. Using atomistic molecular dynamics, the miscibility between ionic liquids (e.g. 1-hexyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide, and 1-ethyl-3-methylimidazolium ethyl sulfate), and polymers (e.g. polyester, nylon6, 6 and polysulfone) has been determined based on energy calculations and conformation analysis. The ionic liquid and polymer chain systems require an intensive level of computing resources to reach equilibrium using an atomistic simulation. Therefore in this work, a simple coarse-grain model and force fields have been developed for the ionic liquid/polymer system, and verified with atomistic simulations and experimental measurements. Utilizing the force-field coarse-grain simulation, the interfacial tensions and contact angles between ionic liquids and polymer films have been determined. These computational efforts will also provide molecular design guidance for the next generation of ionic liquid/polymer composites.

Most organic molecules pack in such a way to minimise free space therefore exhibiting minimal void volume and hence permanent porosity is rare. However, previously we have shown that tetrahedral organic cages can be synthesized and then desolvated to generate porous crystals that adsorb small guest molecules such as nitrogen, hydrogen, methane and carbon dioxide. We have also shown that it is possible to control the particle size of these systems by altering the building blocks used within the makeup of the material. These all exhibit a 3D-diamondoid pore network and by altering the modulus there is an impact on the pore size; as a result the diffusion of gases through them changes. Upon the generation of a bespoke force field, it has been possible to simulate how the diffusion of small gases alter dependant on their particle size. Using molecular dynamic simulations we have unlocked phenomena such as gas selectivity, rare-event hopping and displacement of gases to regions previously considered inaccessible; all of which help to rationalize experimental observations. The aim here is to predict materials which show good selectivity to one gas over another. In the future, there is much scope to use this force field to understand the uptake of larger guests such as halogens and solvents within a whole host of different cage systems leading on the use of MD analysis for in silico screening of cage materials for particular molecular separations. If reliable, this could be faster than the associated sorption experiments. We will also investigate phenomena which are difficult to study by direct experiments, such as mobility of guests into formally occluded voids, with the view to unlocking on why such materials are highly porous.

Although the first reports on zeolite membranes can be traced back to the 1940's, it is only since the 1990's that renewed research efforts were devoted to achieve this goal. To manufacture highly selective supported zeolite membranes, a deposition process to form crack-free, compact, polycrystalline zeolite thin films on porous substrates is essential. Despite the promising proof-of-concept demonstrations, commercial implementation is lagging behind because cost-effective, reliable and environmentally benign thin film deposition methods that can be scaled up to produce commercially relevant film quantities do not exist. Zeolite membrane technology for industrial-scale operations depends on reliable manufacturing that can generate hundreds to thousands of square meters of membrane area and achieve essential membrane characteristics: continuity with low defect density, appropriate out-of-plane orientation, and thin membrane thickness. I will describe an emerging potentially scalable zeolite membrane fabrication method based on zeolite nanosheets. This concept was introduced by our research group about a decade ago and is based on materials with structures intermediate between those of crystalline zeolite frameworks and typical layered materials, such as clay minerals. In these "layered zeolites", each layer includes a porous network (similar to zeolites), while the gallery between layers (as in clays) provides the ability for intercalation and exfoliation. Layers with different sizes of apertures are available, and recent progress in exfoliation techniques is enabling the synthesis of nanosheet suspensions for coatings. In addition to enabling thin film formation, zeolite nanosheets can find use in the synthesis of new catalytic materials. Recent progress in novel catalyst assembly from zeolite nanosheets will be presented.

Advanced porous membranes are of significant importance to dozens of industries including chemicals, oil and gas, automobiles, batteries, semiconductors, food and beverage, biotech and pharmaceutics, waste treatment, environmental protection and remediation by means of filtration or separation. Organic polymeric membranes currently dominate these markets due to their bendable feature and relatively low manufacture cost; however, these organic polymeric membranes suffer from several drawbacks, such as low stability at elevated temperature, low stability in acids and bases, swelling in organic solvents, and fast degradation in oxidative environments. Ceramic membranes, with the advantages of high chemical, thermal and mechanical stability, should be the attractive alternatives to polymeric varieties; however, ceramic membranes have not been widely adopted due to their high manufacture cost, rigid structure, low packing density, and low throughput. It has been a long time dream to make a membrane with both the advantages of polymeric membranes and ceramic membranes. The advantages of nanoscience and nanotechnology make such a dream a reality. Using titania nanowires, Novarials has developed a Bendable Ceramic Paper Membrane platform technology. Titania nanowires are thin strands having diameters in the range of about 10nm to about 100nm, and lengths of from a few microns to tens and even hundreds of microns. Titania nanowires are prepared by cost effective hydrothermal process, and the paper-like ceramic membranes are fabricated by wet laid process. The membranes are porous, bendable/flexible and sufficiently strong, suitable for nanofiltration and ultrafiltration. Potential advantages of these membranes are low manufacturing cost, high porosity, superior chemical and thermal stability and for TiO2, the ability to react with UV light to remove organic material. The presentation will provide detailed information of Novarials Bendable Ceramic Paper Membranes.

Specific surface area is a critical performance characteristic for separation membranes. Frequently, higher surface area is achieved at the expense of reduced mechanical strength. This talk will describe a method for precisely controlling the specific surface area of a given porous membrane without compromising the strength. Silica nanoparticles (12 and 22 nm diameter) were infiltrated into porous membranes that had been created via freeze-casting and sintering a gel formed with silica nanoparticles and kaolinite clay particles. After infiltration, the nanoparticles were secured in place with partial sintering. This infiltration process could be repeated multiple times, allowing the resulting specific surface area to be precisely controlled. (Values up to hundreds of square meters per gram were obtained.) The relationships between surface area, porous microstructure, and permeability were investigated and will be described. Characteristics of the infiltrated membranes (e.g., specific surface area) before and after water flux testing were also evaluated and found to be unchanged. Because the principles of infiltration and securing with sintering involve physical versus chemical interactions, the approach should also be possible with other types of membrane materials and particles.

Anodic aluminum oxide (AAO) nanoporous templates formed on planar Al foils have been widely used for synthesis and self-assembly of nanowires, nanodots, and photonic crystals, while free-standing AAO membranes have been used for catalysis and filtration applications. However, there has not been much foray into the synthesis of AAO on curved surfaces such as Al wires 10 to100&’s of µm in diameter, which can lead to exciting, new applications. For example, it is possible that AAO templates on wires can be inserted inside catheters in biomedical devices and used as sensors for bioanalyte detection. Similarly, multifunctionality can be added to Al wire ‘meshes&’ with applications in energy generation and storage. Thus with a view to expand AAO applications, we performed AAO growth on high purity Al wires and analyzed their pore growth mechanism. Al wires with radius of 50µm were immersed in 0.3M oxalic acid solution maintained at 8°C. Using a first source-measure meter, constant voltage anodization was performed at 40V. These conditions are known to be ideal for forming ordered pores on planar Al foils. Using a second source-measure meter, resistance measurement of the Al wire was made in real time. Since wire resistance is related to its cross section and length, monitoring the resistance allowed us to ascertain the radius of the Al wire during anodization. Pore growth rates obtained from the resistance measurements were found to be severely retarded as compared to pore growth rates on planar Al substrates. Further, the amount of Al₂O₃ (using charge passed from first meter) could be correlated to the growth of the AAO pores (using resistance data from second meter). Contrary to our expectation, the depth of AAO pores calculated from the charge passed data showed a marked deviation from the depth of AAO pores calculated with the resistance data. We found that this deviation occurred at a critical radius of 35 µm for a 50µm radius wire. Cross section SEM studies on anodized wire segments indicated that the pore growth fronts rarely had circular cross sections and many instances of pore merging and cracking was observed at high pore depths. These results along with the retarded growth rates suggest that AAO pore growth on curved surfaces occur under non equilibrium conditions and is dominated by stress effects. Sustained growth of AAO pores is not possible as it leads to pore closure and cracks in the AAO film. However, nanoporous AAO can be grown on Al wires up to a critical pore depth (~ 15µm for a 50µm radius wire) at which point stress relaxation occurs either via cracking of the AAO film or via pore merging. This phenomena coincides with the deviation in estimated radius calculated from charge passed and measured Al wire resistance data. The study thus sets up an upper limit to the depth of AAO pores possible on Al wires before stress relaxation effects cause damage to the porous structure of the AAO.

Biofiltration membranes currently used (e.g. for medical blood filtration therapies) are typically prepared from polymers and often show a wide pore size distribution. Furthermore, sterilization is challenging and adhesion of various protein and immune components frequently occurs. A good way to overcome some of these aforementioned drawbacks may arise from metal oxide membranes formed by electrochemical anodization. This simple and low cost technique, widely used for corrosion protection, provides self-organizing nanostructures if electrolytes containing etching / complexing agents are used. The competition between solvatization and compact oxide formation leads to an almost perfect hexagonal array of oxide nanopores or nanotubes aligned perpendicular to the substrate. Anodization time and etching rate define the tube length; the diameter of the channels is mainly controlled by the applied voltage. Most notably, arrays from anodic aluminium oxide (AAO) and titanium oxide (ATO) have attracted great scientific and technological interest in recent years for their manifold applications: e.g. as templates for nanotube formation, in drug delivery, or the use of semi conductive ATO&’s in dye sensitized solar cells, photocatalysis and gas sensors. Although free-standing membranes with through-hole morphology would also be favorable for non-filtering applications, there are only few reports due to the fragile nature of the membranes. Usually, very thick membranes (of some hundred µm) were tested for their permeability and were of low efficiency. Herein, we would like to present strategies to obtain thin and simultaneously stable AAO and ATO membranes. A key role in producing membranes is the lift-off process from the substrate, followed by opening the closed bottoms. Common ultrasonic splitting destroys the membranes, so electrochemical pulsing or other approaches have to be used. Furthermore, we will show how curling of the resulting membranes can be anticipated. Improved methods for opening the membranes prevent formation of “nano grass” on its surface. Additionally, alternative pathways to obtain stable filters, comprising completely anodized metal foils and stabilizing grit structures (within and on top of the membranes), will be presented. Finally, the effect of functionalization of the hydrophilic membranes on filtering efficiency will be discussed.

Free volume in polymeric materials, typically in less than 1 nm in scale, derived from packing disorder, and free volume element size and shape change in time and space since organic chains are dynamically flexible. Ordinarily, free volume elements in polymers have a wide range of sizes and topologies, and this broad range of free volume element sizes compromises the polymer&’s ability to perform molecular separations. In this presentation, we present the importance of free volume structures in dense, vitreous polymers that enable outstanding molecular and ionic transport along with separation performance surpassing the separation limits obeyed by traditional polymers. The unusual microstructure in these materials can be systematically tailored using thermally-driven “molecular rearrangement” processes. Free volume topologies can be tailored by controlling the degree of rearrangement, flexibility of the original chain, and judicious inclusion of small dopant molecules. Most of all, the greatest benefit of these thermally rearranged-polymers is the ability to control their separation performances for specific gas applications including CO2 capture from flue gas by using various polymer structures and templating molecules with heating time and temperature. On the other hand, for high temperature fuel cell application, extensive efforts have been made to develop sulfonated hydrocarbon polymers such as poly(phenylene)s, poly(arylene, ether sulfone)s, polyimides as potential PEMs. Herein we introduce our strategies of novel sulfonated hydrocarbon polymers and their performance as PEM based on effective nanochannel formation. The size of hydrophilic nano ion channel is one of the critical issues that need to be considered in transporting protons. Lithium ion transport using high temperature polymers is also very important in battery application along with high cell density and fast charging-discharging cycles. A novel polymer with tuned nanochannels can be applied as high temperature lithium ion battery separator as well. In this presentation, we present the importance of nano ion channels in polymers for potential application in separation and energy industry.

Improvements to the performance of thin solid polymer electrolytes for use as proton exchange membranes (PEMs) are critical for the advancement of the electrochemical energy devices such as direct methanol fuel cells (DMFCs). The essential properties for polyelectrolyte PEM used in DMFCs include: high ionic conductivity, low fuel/charge crossover, and mechanical stability. PEM fabrication by spray-assisted layer-by-layer (LbL) assembly of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) and poly(diallyl dimethyl ammonium chloride) [sPPO/PDAC] onto an electrospun fiber mat (EFM) scaffold has been shown to provide ionic conductivity comparable to that of the industry standard, Nafion®, while achieving a two order of magnitude reduction in methanol crossover. Electrospinning is used to create porous nanoscale polymer fiber scaffolds to provide mechanical support as well as mimic the percolated, fibrillar structure of water-swollen Nafion®. Poly(trimethyl hexamethylene terephthalamide) [PA 6(3)T], was used as the electrospun nanofiber “endo-skeleton” for the PEM due to its inherently high mechanical strength, tunable fiber diameter, high porosity, and relative ease of fabrication. Coating the PA 6(3)T EFMs by the vacuum-assisted spray-LbL technique produces composite membranes with conformally coated fibers throughout the bulk of the EFM and gives nanometer control of the thickness of the coating. Since the LbL process treats each fiber as an individual growth surface, entire EFMs (thickness ranging from 25 - 80 mu;m) can be filled up to 70%with less than 1 mu;m thick LbL coatings, while retaining up to 50% of the pristine LbL conductivity. In the absence of vacuum, the spray-LbL process forms a film covering all the pores of the EFM without penetrating into the fibers, thus creating a coherent methanol-impermeable capping layer. The mechanical properties of these composite LbL/EFM membranes are drastically improved over those of the LbL film alone, exhibiting the stiffness of PDAC/sPPO films when dry and the strength of the underlying EFM when hydrated. Improvements in the mechanical performance of the composite LbL/EFM PEMs are achieved by manipulating the structure of the underlying nanofiber matrix by heat treatment of the EFM post-spinning to increase the number of weld points between fibers and thus create a stronger fiber network. The dimensional stability of the composite PEMs under humidity cycling is superior to most conventional polyelectrolyte membranes, and the mechanical durability of the LbL/EFM PEMs was also found to be comparable to Nafion®. The composite LbL/EFM PEMs have been tested in a DMFC and preliminary results show higher open circuit voltage compared to Nafion®, as the result of reduced methanol permeability and comparable membrane impedance. Further optimization of the membrane electrode assembly and PEM conditioning indicate the potential for improved fuel cell output.

Assimilating hydrophilic hollow polymer spheres (HPS) into Nafion matrix by a loading of 0.5 wt% led to a restructured hydrophilic channel, composed of the pendant sulfonic acid groups (-SO3H) and the packed hydrophilic hollow spheres. The tiny hydrophilic hollow chamber was critical to retaining moisture and facilitating proton transfer in the composite membranes. To obtain such a small cavity structure, the synthesis included selective generation of a hydrophilic polymer shell on silica microsphere template and the subsequent removal of the template by etching. The hydrophilic HPS (100-200 nm) possessed two different spherical shells, the styrenic network with pendant sulfonic acid groups and with methacrylic acid groups, respectively. By behaving as microreservoirs of water, the hydrophilic HPS promoted Grotthus mechanism and hence enhanced proton transport efficiency through inter-sphere path. In addition, the HPS with the -SO3H borne shell played a more effective role than those with the -CO2H borne shell in augmenting proton transport, in particular under low humidity or at medium temperatures. Single H2-PEMFC test at 70oC using dry H2/O2 further verified the impactful role of hydrophilic HPS in sustaining higher proton flux as compared to pristine Nafion membrane.

Proton exchange membrane fuel cells (PEMFC) have received attention to become alternative energy sources for stationary, vehicles and portable devices, because of their high efficiency, environmental friendly fuels and various potential applications. One of the key issues of proton exchange membranes (PEMs) is to get high proton conductivity and excellent mechanical properties. Therefore, many researches of hydrocarbon polymer membranes have been investigated for alternative PEM materials. These membranes exhibit excellent chemical, thermal stabilities and high proton conductivity. However, their major problem, such as excessive water swelling and weak durability, are unsuitable to satisfy practical PEMFC operations. Cross-linking is a simple and efficient method to reducing water uptake and also enhancing mechanical properties and dimensional stability. Numerous researchers have reported such as ionically, covalent cross-linking and photo cross-linking. However, most of these methods suffer from loss of proton conductivity or the complicated preparation process problems. In this study, end group cross-linking methods via specific reaction were introduced to PEMs. The reaction has the advantages of short reaction time, a wide range of functionalities, a high yield and superior region selectivity. We expected end group cross-linking is one of the effective ways for highly sulfonated PEMs because end group cross-linking improves PEM properties without loss of acid sites or affecting chemical structure change of the polymer main chain. End group cross-linked membranes with high degree of sulfonation showed improved dimensional and mechanical stability, while enhanced the proton conductivity and long term stability.

Anion exchange membrane fuel cells (AEMFCs) are an alternative to proton exchange membrane fuel cells (PEMFCs) with potential benefits that include low cost (i.e. platinum-free), facile electrokinetics, low fuel crossover, and use of CO-resistant metal catalysts. In spite of these advantages, widespread use of AEMFCs has not been achieved. More highly conductive anion exchange membranes (AEMs) are needed that do not exhibit impaired physical properties. With the objective of maximizing conductivity and stability, one promising strategy is to develop a membrane material with a well-developed nanochannel structure. We have developed synthetic schemes for preparing anion-conductive multiblock copolymers that should exhibit nanophase separation due to the presence of hydrophobic and hydrophilic segments. Nanochannel morphology can be tuned by controlling the hydrophilic segment length, the polarity difference of each block, and optimizing ion exchange capacity. Extensive nuclear magnetic resonance (NMR) methods are employed to examine exact molecular structure and quantitative ion and liquid transport dynamics inside the AEM. Ultimately, these new multiblock copolymers will be used as membranes or ionomers in hybrid polymer electrolyte fuel cells and alkaline direct methanol fuel cells. Ex-situ characterization techniques include conductivity, water uptake, and fuel permeability. In-situ fuel cell performance testing is also being conducted.