Pervaporation performance of novel chitosan‐POSS hybrid membranes: Effects of POSS and operating conditions

Four types of polyhedral oligosilsesquioxane (POSS)–octaanion, octaammonium, octanitrophenyl, and octaaminophenyl–were incorporated into chitosan (CS) to fabricate inorganic–organic hybrid membranes. The hybrid membranes were employed for the pervaporation dehydration of ethanol aqueous solutions. The performance of the hybrid membranes was found to be influenced by the type and loading amount of POSS. In comparison with the neat CS membranes which showed a separation factor of 65.2 for 10 wt % water in the feed at 303 K, the hybrid membranes containing 5 wt % of octaanion and octaaminophenyl POSS showed high separation factors of 305.6 and 373.3, respectively. The effects of the operating conditions such as the feed composition and temperature on the pervaporation performance of the membranes were investigated. Activation energies for permeation in the membranes were estimated from Arrhenius relationship. The activation energies for ethanol permeation in the hybrid membranes were much higher than that in the CS membrane, which may account for the large enhancements in the selectivity of the hybrid membranes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Sulfonated polybenzimidazoles: Proton conduction and acid–base crosslinking

A series of soluble, benzimidazole‐based polymers containing sulfonic acid groups (SuPBI) has been synthesized. SuPBI membranes resist extensive swelling in water but are poor proton conductors. When blended with high ion exchange capacity (IEC) sulfonated poly(ether ether ketone) (SPEEK), a polymer that has high proton conductivity but poor mechanical integrity, ionic crosslinks form reducing the extent of swelling. The effect of sulfonation of PBI on crosslinking in these blends was gauged through comparison with nonsulfonated analogs. Sulfonic acid groups present in SuPBI compensate for acid groups involved in crosslinking, thereby increasing IEC and proton conductivity of the membrane. When water uptake and proton conductivity were compared to the IEC of blends containing either sulfonated or nonsulfonated PBI, no noticeable distinction between PBI types could be made. Comparisons were also made between these blends and pure SPEEK membranes of similar IEC. Blend membranes exhibit slightly lower maximum proton conductivity than pure SPEEK membranes (60 vs. 75 mS cm^?1) but had significantly enhanced dimensional stability upon immersion in water, especially at elevated temperature (80 °C). Elevated temperature measurements in humid environments show increased proton conductivity of the SuPBI membranes when compared with SPEEK‐only membranes of similar IEC (c.f. 55 for the blend vs. 42 mS cm^?1 for SPEEK at 80 °C, 90% relative humidity). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3640–3650, 2010     

Hierarchical structure in polymer‐based drug delivery systems as probed by calorimetric measurements

Thermoporosimetry (TPM), a differential scanning calorimetry technique that relies on the shift of transition temperatures caused by the confinement of liquids, was applied to elucidate the complex morphology of drug‐loaded polymeric microcapsules prepared by the emulsion solvent evaporation method. For the very first time, TPM has been applied simultaneously with two liquids as structural probes. It was found that Miglyol, which dissolves the selected drug (Ibuprofen), is confined inside vesicles having a mean radius of 26.3 nm, whereas water, which is the continuous phase, is trapped inside a swollen polymeric network of Eudragit with an average mesh radius of 1.7 nm. A proposed hierarchical structure is given, which predicts that Eudragit microcapsules are formed from a collection of inert oil vesicles partitioned by polymeric Eudragit membranes swollen by water. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1939–1945, 2010     

Anion exchange membranes: Current status and moving forward

This short review is meant to provide the reader with highlights in anion exchange membrane research, describe current needs in the field, and point out promising directions for future work. Anion exchange membranes (AEMs) provide one possible route to low platinum or platinum-free fuel cells with the potential for facile oxidation of complex fuels beyond hydrogen and methanol. AEMs and related stable cationic polymers also have applications in energy storage and other electrochemical technologies such as water electrolyzers and redox flow batteries. While anion exchange membranes have been known for a long time in water treatment applications, materials for electrochemical technology with robust mechanical properties in thin film format have only recently become more widely available. High hydroxide and bicarbonate anion conductivity have been demonstrated in a range of AEM formats, but intrinsic stability of the polymers and demonstration of long device lifetime remain major roadblocks. Novel approaches to stable materials have focused on new types of cations that employ delocalization and steric shielding of the positive center to mitigate nucleophilic attack by hydroxide. A number of promising polymer backbones and membrane architectures have been identified, but limited device testing and a lack of understanding of the degradation mechanisms in operating devices is slowing progress on engineered systems with alkaline fuel cell technology. Our objective is to spur more research in this area to develop fuel cell systems that approach the costs of inexpensive batteries for large-scale applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1727–1735, 2013     

Characterizing fracture energy of proton exchange membranes using a knife slit test

Pinhole formation in proton exchange membranes (PEM) may be caused by a process of flaw formation and crack propagation within membranes exposed to cyclic hygrothermal loading. Fracture mechanics can be used to characterize the propagation process, which is thought to occur in a slow, time‐dependent manner under cyclic loading conditions, and believed to be associated with limited plasticity. The intrinsic fracture energy has been used to characterize the fracture resistance of polymeric material with limited viscoelastic and plastic dissipation, and has been found to be associated with long‐term durability of polymeric materials. Insight into this limiting value of fracture energy may be useful in characterizing the durability of proton exchange membranes, including the formation of pinhole defects. In an effort to collect fracture data with limited plasticity, a knife slit test was adapted to measure fracture energies of PEMs, resulting in fracture energies that were two orders of magnitude smaller than those obtained with other fracture test methods. The presence of a sharp knife blade reduces crack tip plasticity, providing fracture energies that may be more representative of the intrinsic fracture energies of the thin membranes. Three commercial PEMs were tested to evaluate their fracture energies (G_c) at temperatures ranging from 40 to 90 °C and humidity levels varying from dry to 90% relative humidity (RH). Experiments were also conducted with membrane specimens immersed in water at various temperatures. The time temperature moisture superposition principle was applied to generate fracture energy master curves plotted as a function of reduced cutting rate based on the humidity and temperature conditions of the tests. The shift with respect to temperature and humidity suggests that the slitting process is viscoelastic in nature. Also such shifts were found to be consistent with those obtained from constitutive tests such as stress relaxation. The fracture energy is more sensitive to temperature than on humidity. The master curves converge at the lowest reduced cutting rates, suggesting similar intrinsic fracture energies; but diverge at higher reduced cutting rates to significantly different fracture energies. Although the relationship between G_c and ultimate mechanical durability has not been established, the test method may hold promise for investigating and comparing membrane resistance to failure in fuel cell environments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 333–343, 2010     

Radiation‐grafted ion‐exchange membranes: Influence of the initial matrix on the synthesis and structure

A series of commercial fluoropolymer films was irradiated with an electron beam, grafted with styrene, and sulfonated. The influence of the initial fluoropolymer on the grafting yields and the properties of the grafted and sulfonated membranes were investigated. The same synthesis procedure can be followed for most fluoropolymers and samples with a similar degree of grafting, and a homogenous polystyrene distribution can be prepared by varying the absorbed dose. The main difference among different fluoropolymer‐based membranes is the water uptake from liquid water that has a roughly linear dependence on the crystallinity of the sample. The more amorphous the initial material, the greater the water uptake. Mechanical properties of the membranes at 50% relative humidity differ less than those of the starting materials and are comparable to those of Nafion® 105. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3008–3017, 2001     

Simulation study of the equilibrium morphology in ionomers with different architectures

The influence of the side chain and the backbone segment length on the shape of the hydrophilic clusters in an ionomer with sulfonate‐terminated side chains is investigated by molecular dynamics computer simulations. Different ionomer architectures, ranging from Nafion‐like molecules to ionomer structures with extremely long side chains and backbone segments, are analyzed. It is shown that the size and the sulfonate population of hydrophilic clusters are differently affected by the variation of the backbone length in homologous membranes. Although the clusters swell when the backbone length is increased, they contain fewer head groups, and the average sulfonate–sulfonate separation in these swollen clusters becomes larger. An increase in the equivalent weight (EW) of homologous membranes thus hinders proton transport through hydrophilic channels. We also have shown that larger sulfonate clusters are formed in modified membranes with longer side chains. Compared to the case of membranes with shorter side chains but the same EW, those with longer side chains have a higher proton diffusivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

Nanoporous and proton conductive hydrophobic–hydrophilic copolymer thermoset membranes

Copolymers of hydrophobic diglycidyl ether of bisphenol A (DGEBA) vinyl ester (VE) and hydrophilic 2‐acrylamido 2‐methyl 1‐propane sulfonic acid (AMPS) were evaluated as proton conducting membranes for fuel cell applications. Membranes were synthesized using free radical copolymerization in the presence of a common solvent for both monomers, dimethyl formamide (DMF), followed by solvent removal by supercritical CO₂ to induce porosity. Micrographs revealed pore sizes below 60 nm with porosity proportional to the initial solvent fraction used. Studies on the states of water showed that the presence of this pore volume significantly altered the freezable water fraction at equivalent AMPS concentrations. Comparison of the moles of water per mole of sulfonic acid (λ) between copolymer membranes and AMPS monomer solutions showed that the nonfreezable water (λ|_nonfr) was depressed at high AMPS concentrations, suggesting that differences in interatomic distances between sulfonic acid groups might alter λ|_nonfr. The highest average through plane conductivity of membranes was determined to be 30 mS/cm and was comparable to that of Nafion®117 (27 mS/cm). The effective proton mobility, μ_eff, was calculated and suggested to be a parameter used to capture the effects of membrane structure and swelling while acting as a comparison between different membrane types. Fuel cell tests on membranes at low ion exchange capacities were compared to Nafion®117, with suggestions on improvements of copolymer structures for improved performance. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1245–1255, 2010     

Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter δ, surface tension γ, viscosity η and boiling temperature were used to generate mixtures for electrospinning cellulose acetate (CA) (degree of substitution, DS = 2.45). Although none of these solvents alone enables continuous formation of fibers, mixing DMAc with either acetone or acetic acid produced suitable solvent systems. The 2:1 acetone:DMAc mixture is the most versatile mixture because it allows CA in the 12.5–20% concentration range to be continuously electrospun into fibrous membranes. These CA solutions have η between 1.2 and 10.2 poise and γ around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to ～1 μm. Fiber sizes generally decrease with decreasing CA concentrations. The nature of the collectors affects the morphology as well as packing of fibers. Fibers collected on paper have more uniform sizes, smooth surfaces, and fewer defects, whereas fibers collected on water are more varied in size. Electrically conductive solid collectors, such as Al foil and water, favor more tightly packed and less porous membranes. Porous collectors, like paper and copper mesh, produce highly porous membranes. The pores in membranes collected on the Al foil and paper are much better interconnected in the planar directions than those in membranes collected on water. There is evidence that electrospinning induces order in the fibers. Deacetylation of CA membranes is more efficient and complete in NaOH/ethanol than in aqueous NaOH, producing DS values between 0.15 and 2.33 without altering fiber surfaces, packing, or organization. The fully regenerated cellulose membranes are similarly hydrophilic as commodity cellulose fibrous matrices but absorb nearly 10 times as much water. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119–2129, 2002     

Secondary relaxations and electrical conductivity in hyperbranched polyester amides

Broadband dielectric spectroscopy is used to investigate molecular dynamics and charge transport in three hyperbranched polyester amides with hydroxyl, phenyl, and stearate terminal groups. At higher temperatures, the dielectric spectra are interpreted in terms of hopping conduction in a spatially randomly varying energy landscape, whereas two secondary dipolar relaxations attributed to librations of the terminal and amide groups dominate the low temperature regime. Despite a shift of more than 3 decades in the dc conductivity upon variation of the end groups, the Barton–Nakajima–Namikawa relation is shown to hold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1651–1657, 2010     

Proton‐conductive polymer nanocomposite membranes prepared from telechelic fluorinated polymers containing perfluorosulfonic acid side chains

New classes of fluorinated polymer–polysilsesquioxane nanocomposites have been designed and synthesized. The synthesis method includes radical polymerization using the functional benzoyl peroxide initiator for the telechelic fluorinated polymers with perfluorosulfonic acids in the side chains and a subsequent in situ sol–gel condensation of the prepared triethoxylsilane‐terminated fluorinated polymers with oxide precursors. The telechelic polymer and nanocomposites have been carefully characterized by ¹H and ¹⁹F NMR, FTIR, TGA, and TEM. The ion‐exchange capacity (IEC), water uptake, the state of the absorbed water, and transport properties of the composite membranes have been extensively studied as a function of the content and structure of the fillers. Unlike the conventional Nafion/silica composites, the proton conductivity of the prepared membranes increases steadily with the addition of small amounts of the polysilsesquioxane fillers. In particular, the sulfopropylated polysilsesquioxane‐based nanocomposites display proton conductivities greater than Nafion. This is attributed to the presence of pendant sulfonic acids in the fillers, which increases IEC and offers continuous proton transport channels between the fillers and the polymer matrix. The methanol permeability of the prepared membranes has also been examined. Lower methanol permeability and higher electrochemical selectivity than those of Nafion have been demonstrated in the polysilsesquioxane‐based nanocomposites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Energy diagrams and stability restrictions for electroelastic generators

The relation between electric and mechanical properties of dielectric elastomers allows using them as energy convertors under some conditions. The process is based on the relations between mechanical and electrical energy stored on the material. In this work, cycles of maximal mechanical energy to be converted into electrical energy are presented. The purpose of this article is to give a general formulation of electroelastic generator relations considering (1) Mooney‐Rivlin materials, (2) floating sample between electrodes and sample with compliant electrodes, and (3) explicit thermodynamic stability criteria. Estimations on the maximal energy to be converted are made. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2023–2028, 2010     

Aquaporin-Based Biomimetic and Bioinspired Membranes for New Frontiers in Sustainable Water Treatment Technology: Approaches and Challenges

Biomimetic and bioinspired membranes are the efficient membrane technology when it comes to multiple usage scenarios, including next generations of biomaterials within the commercial separation applications, as well as, water and wastewater treatment technologies. In recent years, aquaporin biomimetic membranes for water separation have raised considerable interest. These membranes have displayed distinguished properties and outstanding performances, as diverse interactions, varying selective transport mechanisms, superior stability, maximum resistance to membrane fouling, and distinct adaptability. The biomimetic membranes have made significant contributions when it comes to water stress, environmental threats and energy. It has the potential to produce clean water more efficiently than reverse osmosis membranes (RO), while saving up to 80% of the energy used for desalination processes. More than half of the 15000 desalination plants around the world utilize RO technologies, and the implementation of biomimetic membranes on a large scale could save hundreds of millions of dollars in energy cost annually (potential savings of $1.45 million/year for 100 ML/day desalination plant). This paper discusses the interplay of the main components of aquaporin biomimetic membranes: aquaporin proteins, block copolymers for aquaporin proteins reconstitution, and polymer-based supporting structures. We focus specifically on the challenges and review recent developments on the interplay between aquaporin proteins and block copolymers. The recent efforts in embedding reconstituted aquaporin proteins in membrane designs that are based on conventional thin film interfacial polymerization techniques are evaluated. In addition, emerging challenges and opportunities for biomimetic membranes are studied from the perspective of current and future applications.     

A molecular dynamics simulation study of three polysulfones in dry and hydrated states

Molecular dynamics (MD) simulations of three polysulfones (poly(ether sulfone) PESU, poly(phenylene sulfone) PPSU and polysulfone PSU) in dry and hydrated states were undertaken in order to study the specific interactions between water and glassy polymer matrices of the same structural family. Dry polysulfone models were generated using a hybrid pivot Monte Carlo‐MD single‐chain sampling technique and the resulting relaxed densities were found to be in close agreement with experimental data. Hydrated systems are found to reproduce quite well volumetric changes experimentally observed. The concentrations of sulfonic groups can explain qualitatively their different water solubilities. Water is preferentially hydrogen‐bonded to two sites which either link two polymer sites, or one polymer site and another water, or two other waters. A detailed analysis of these water bridges that are formed is presented. Only a small quantity of potential bridging sites are occupied for water contents near the experimental saturation. The free fractional volumes, the probe accessible volumes, the swelling of the polymers, the water‐polymer interactions and the hydrogen bond lifetimes, are also presented for these polysulfones. Water‐water interactions and water clusters are found to be more important in the more hydrophilic PESU in comparison to the less hydrophilic PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Dependence of methanol permeability on the nature of water and the morphology of graft copolymer proton exchange membranes

Novel polymers with controlled microstructures were prepared and studied to further advance the understanding of structure–property relationships of proton conducting membranes. PAN‐g‐macPSSA membranes, which contained poly(styrenesulfonic acid) (PSSA) grafts of defined graft length, are compared with PVDF‐g‐PSSA membranes, prepared by radiation‐grafting, and Nafion® 117. The intrinsic properties of PAN‐g‐macPSSA membranes are insensitive to the macromonomer graft length but are highly dependent on the ion exchange capacities (IEC). Increasing the IEC increases the content of free water absorbed by the membrane. Self‐diffusion coefficients of water in water‐swollen PAN‐g‐macPSSA were found to be similar to that of N117, despite PAN‐g‐macPSSA's higher water content. Of the polymers studied, PAN‐g‐macPSSA exhibited the lowest methanol permeability, which is explained on the basis of it containing a more tortuous ionic network. Methanol permeability decreased with decreasing volume of free water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2240–2252, 2006     

Synthesis and characterization of poly(arylene ether ketone)s bearing pendant sulfonic acid groups for proton exchange membrane materials

A bisphenol monomer (2,5‐dimethoxy)phenylhydroquinone was prepared and further polymerized to obtain poly(arylene ether ketone) copolymers containing methoxy groups. After demethylation and sulfobutylation, a series of novel poly(arylene ether ketone)s bearing pendant sulfonic acid group (SPAEKs) with different sulfonation content were obtained. The chemical structures of all the copolymers were analyzed by ¹H NMR and ¹³C NMR spectra. Flexible and tough membranes with reasonably good mechanical properties were prepared. The resulting side‐chain‐type SPAEK membranes showed good dimensional stability, and their water uptake and swelling ratio were lower than those of conventional main‐chain‐type SPAEK membranes with similar ion exchange capacity. Proton conductivities of these side‐chain‐type sulfonated copolymers were higher than 0.01 S/cm and increased gradually with increasing temperature. Their methanol permeability values were in the range of 1.97 × 10^?7–5.81 × 10^?7 cm²/s, which were much lower than that of Nafion 117. A combination of suitable proton conductivities, low water uptake, low swelling ratio, and high methanol resistance for these side‐chain‐type SPAEK films indicated that they may be good candidate material for proton exchange membrane in fuel cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Effect of crosslinking on the secondary relaxation in polyvinylethylene

The effect of network formation on the secondary (Johari–Goldstein) β‐relaxation was investigated for polyvinylethylene (PVE). Crosslinking affects the segmental (α‐) process in the usual fashion, the networks exhibiting slower and more temperature‐sensitive dynamics. However, the effect on the β‐process is the opposite. The secondary relaxation becomes faster and the activation energy slightly decreases with crosslinking. The strength of the intermolecular cooperativity governing the behavior of the α‐process was assessed using the coupling model, with consistent results obtained from analysis of both the timescale separating the α‐ and β‐relaxations and the activation energy for the latter. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 582–587, 2010     

Sample‐to‐sample fluctuations in heterogeneous DNA

We studied the structure of heterogenous DNA in the native state. There are two different regimes in the sample‐to‐sample fluctuations of the free energy in the native state, which can be interpreted via the concept of local free energy of base pairs. In the first low‐temperature frozen regime, local free energies are random and there are large sample‐to‐sample fluctuations for short DNAs. In the high‐temperature molten regime, the weakly bounded base pairs are opened and do not give random contribution to the free energy of native DNA. As a result, sample‐to‐sample fluctuations are suppressed in the molten regime. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Water sorption and diffusion coefficients of protons and water in PVDF-g-PSSA polymer electrolyte membranes

Water sorption properties, proton NMR spectra, and diffusion of water and protons in poly(vinylidene fluoride)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) polymer electrolyte membranes were studied. Sorption curves for the membranes with different degrees of grafting in protonated and Na⁺ form were measured by equilibrating the membranes over saturated salt solutions. The membrane water content was found to be sensitive to changes in relative humidity (RH). The water/sulfonic acid ratio λ for the protonated samples was around 2 at 20% RH and increased to λ ∼ 30 at 100%. Proton NMR, pulsed field gradient proton NMR (PFG-NMR), and impedance measurements were made on membranes with different λ. In the proton NMR spectra only one peak was found, originating from the water in the membrane. The chemical shift of the peak was found to be dependent on the counterion and the water content. The water self-diffusion coefficients D_H2O, measured by PFG-NMR, increased with degree of grafting and water content of the membranes. The proton conductivity and the calculated proton mobility decreased more steeply than the D_H2O with decreasing water content. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2893–2900, 1999