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The dynamics of hydronium ions and methanol molecules in hydrated SPAES and blend membranes are investigated via molecular dynamics simulations using the COMPASS force field. In addition to calculating the diffusion coefficients as a function of the hydration level, an amorphous cell with a specific composition of H2O molecules and H3O+ determined from the experimental data is constructed and tested. The water and methanol diffusion coefficients are considerably smaller at lower hydration levels and room temperature. The diffusion coefficient of the water and methanol molecules increases with increases in the hydration level, and this is in good agreement with experiment data. Analysis of the pair correlation functions supports the experimental observations of the membrane performance with hydration related to the water and methanol diffusion behavior in hydrated SPAES and blend membranes.

The new hydrophilic–hydrophobic comb-type anion exchange membrane (AEM) was prepared from SEBS grafted with hexyl quaternary ammonium (HQA) and fluorobenzoyl. As confirmed by XRD and TEM, a better phase separation was obtained by adding a highly hydrophobic fluorine-substituted pendant as an enhanced hydrophobic spacer to the conducting head group (which contained a hexyl spacer as a hydrophilic unit). The HQA-F1-SEBS and HQA-F5-SEBS membranes, with fluorobenzoyl and pentafluorobenzoyl pendants, respectively, showed enhanced hydrophobicity compared to their non-fluorinated counterpart (HQA-SEBS). The highest hydroxide ion conductivity (87.0 in water and 14.37 mS cm-1 at 95% RH) was obtained at 80 °C with HQA-F5-SEBS, which exhibited the most thermodynamic incompatibility between hydrophilic and hydrophobic units. The mechanical properties (tensile strength and Young's Modulus) of the HQA-F5-SEBS membrane were also improved; they were almost 2.5 times higher than those of the HQA-SEBS. The HQA-F5-SEBS showed a current density of 500 mA cm-2 at a potential of 0.6 V and a peak power density of 354 mW cm-2. It also showed stable-cell durability for up to 100 hours. Compared with the typical hydrophilic comb-type SEBS membrane and the previously reported SEBS-based AEM, its cell performance was significantly higher.

Poly(dibenzylated benzimidazolium) bromides (Bz-PBI-Br) were converted successfully to OH− ion conducting poly(dibenzylated benzimidazolium) hydroxides (Bz-PBI-hydroxides) by the treatment of KOH. The Bz-PBI-hydroxides obtained in this study showed an excellent alkali tolerance compared to previously synthesized poly(dimethylated benzimidazolium) hydroxides (Me-PBI-hydroxides). According to 1H-NMR analysis, Me-PBI-hydroxides were decomposed during KOH treatment. In order to find out the reason, density functional theory (DFT) calculations of two benzimidazolium structures, e.g., dimethylated benzimidazolium (Me-BI+) and dibenzylated benzimidazolium (Bz-BI+), were performed. Bz-BI+ showed lower electron affinity and OH−-binding energies at the C2 position of the benzimidazolium ring than Me-BI+. These DFT results strongly confirm that Bz-BI+ is less vulnerable to an OH− attack than Me-BI+; this contributes to the enhanced stability and OH− ion conductivity of the Bz-PBI-hydroxides.

The efficient CO2 separation process depends on the trade-off among permeability and selectivity requirements. In this work, copolymers of polyhedral oligomeric silsesquioxanes (POSS) with cage-like rigid structure and polyethylene glycol (PEG) with good CO2 affinity were synthesized by introducing allyl-POSS and allyl-EO into the side chain of polymethylhydrosiloxane (PMHS) in different proportions. The POSS80PEG20 copolymer fashioned into membrane showed good CO2 separation performance (permeability of 679 barrer and CO2/N2 selectivity of 38.1). The effect of POSS content on morphology, thermal stability and mechanical properties was also investigated. Multilayered composite membranes using POSS80PEG20 copolymer of different concentration as a selective layer, polyacrylonitrile (PAN) support layer and polydimethylsiloxane (PDMS) middle layer were also fabricated to achieve improved mechanical stability. The composite membrane with selective layer concentration of 0.25 wt% (POSS-PEG-0.25) offered optimum CO2/N2 and CO2/O2 selectivity performances. Moreover, the effect of feed pressure on mixed gas permeance was also reported.

Poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymers are prepared with 50% hexyl quaternary ammonium (HQA) and 20% alkyl chains of different chain lengths: C4 (50HQA-20C4-SEBS) and C12 (50HQA-20C12-SEBS). Their physicochemical and electrical properties are investigated for use as novel alkaline anion exchange membranes. In most other comb-type polymers, the alkyl chain is introduced as a hydrophilic spacer unit between the polymer backbone and conducting head group. In the current study, additional alkyl chains are grafted onto the SEBS polymer as hydrophobic side chains as well as typical hydrophilic side chains. Introduction of this extra hydrophobic alkyl spacer group is done to obtain well-connected morphology, increased free volume, enhanced water uptake and related conductivity, together with improved physicochemical properties of the membranes obtained. The results are compared with HQA-functionalized SEBS without the hydrophobic alkyl spacer group (50HQA-20C0-SEBS), and the effects of the alkyl chain lengths on the structure of polymers and physicochemical properties of the corresponding membranes are investigated.

An effective strategy to improve both the conductivity and alkaline stability of anion exchange membranes (AEMs) was proposed by incorporating quaternary ammonium functionalized polyhedral oligomeric silsesquioxane (QPOSS) into quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO). Glycidyltrimethylammonium chloride (GTMAC) was used as the main quaternized reagent for the synthesis of QPOSS. The introduction of QPOSS provided the hybrid membranes with additional ion hopping sites and ion conducting channels. The QPPO-QPOSS membrane with high ion exchange capacity of 4.81 meq g−1 possessed the hydroxide ion conductivity of 8.77 × 10−2 Scm−1 at 80 °C. Meanwhile, the hybrid composite membranes showed enhanced alkaline stability due to the steric hindrance offered by QPPO and QPOSS and good alkaline resistance of long alkyl chain from octaammonium and glycidyl trimethyl ammonium bulky substituents. The residual ratio of hydroxide conductivity of QPPO-QPOSS-3 after being treated with 1 M KOH at room temperature for 1200 h reached 102%. The improved interfacial compatibility among the matrix polymer and filler imparted the hybrid membranes enhanced mechanical properties, good dimensional and thermal stability. The H2/O2 fuel cell using composite membrane of 3 wt% QPOSS relative to QPPO reached a maximum power density of about 288 mWcm−2. The prepared hybrid membrane with promising characteristics exhibited the potential for applications in alkaline anion exchange membrane fuel cells in considering their integrative properties.

Crosslinked polyimides with a pendant piperazinium bromide acting as both the crosslinker and the CO 2 -philic functional group have been developed. These ionic-group-mediated crosslinked polyimide membranes showed excellent thermal, mechanical and chemical stabilities, as well as high tolerance to plasticization. Unlike other typical crosslinked polymers, the pendant piperazinium-mediated crosslinked polyimide membranes displayed high CO 2 permeability of 475.5 Barrer, together with high CO 2 /CH 4 (34.5) and CO 2 /N 2 (18) permselectivities. We also demonstrate that the CO 2 separation performances of these membranes can be tuned by changing the crosslinking method.

Copolymers based on glassy and rubbery units have been developed to take advantages of both domains to enhance solubility and diffusivity. Well-tuned microstructure in copolymers has provided high gas permeability and selectivity. In this study, we report on the syntheses and characterizations of copolymers using poly(ethylene glycol) and high free volume polysulfone. Bulky and flexible bis(phenyl)fluorene moiety is introduced in polysulfone domain. Comparison between conventional bisphenol-A based polysulfone and the polysulfone in this work is made in terms of fractional free volume and gas permeation properties. In the poly(sulfone-co-ethylene glycol), the composition of sulfone/ethylene glycol results in the improvement of thermal and physical properties. Copolymers are characterized using gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, wide angle X-ray diffraction, and gas permeation measurements.

Polybenzimidazoles ( p -PBI and m -PBI) were synthesized by the reaction of 3,3-diaminobenzidine with terephthalic acid or isophthalic acid in polyphosphoric acid at 220 °C for 20 h. These PBI membranes were prepared by two methods: conventional casting (post-membrane fabrication) and direct casting ( in situ fabrication). Their properties were found to be dependant on their polymer structure as well as the membrane casting method used in the fabrication process. p -PBI demonstrated higher ion conductivity and greater mechanical properties than m -PBI. The membrane produced by the direct casting method resulted in higher ion conductivity than that produced by the conventional casting method. For these reasons, p -PBI membrane formed by a direct casting method promises to enhance the performance of proton exchange membrane fuel cells (PEMFCs).

Chemically robust membranes composed of the rubbery copolymers poly(styrene-co-butadiene) and poly(acrylonitrile-co-butadiene) along with the glassy polymer polyvinylchloride are prepared by solution casting, crosslinked with sulfur, and tested for their ability to separate benzene and cyclohexane. These polymer blends are not miscible across all compositions but careful solution casting art is used to create non-equilibrium but homogeneous blends through a process of “forced assembly.” Experimental results show a typical trade-off curve; fluxes increase as selectivity decreases. Increasing the temperature from 25 to 60 °C results in a relatively small decrease in permeate concentration (from 93.9 to 88.3 wt.%) but to an enormous increase in flux by a factor of nearly 20 (from 5.0 to 98.9 kg μm/m 2 h). It is demonstrated that while solubility parameters can be used to correlate the ideal swelling selectivity, they have no descriptive capability for actual membrane performance. Accordingly, a more predictive approach was investigated using group contribution methods in the form of UNIFAQ-FV. Quantitative agreement with experiment is not achieved because the equilibrium model cannot capture diffusion effects, however, the model does predict the best blend formulation (i.e. the optimal composition). Accordingly, multicomponent thermodynamic modeling can serve a limited role in providing a rational methodology for selecting blend components for specific separation or barrier purposes.

Sulfonated poly(arylene ether sulfone) copolymers derived from sulfonated 4,4′-dichlorodiphenyl sulfone (S-DCDPS), 4,4′-dichlorodiphenyl sulfone (DCDPS) and phenolphthalin (PP) were evaluated as polymer electrolyte membranes for direct methanol fuel cells. The change in ion exchange capacity, state of water content, proton conductivity, and methanol permeability with S-DCDPS content are discussed. The proton conductivity increased linearly from 5.1 × 10 –3 to 4.7 × 10 –2 S cm −1 at 30 °C and 95% RH with increasing sulfonation level. However, the methanol permeability increased linearly up to 20 mol% sulfonated monomer content, but then a sudden increase was observed, referred to as the “percolation threshold”, at sulfonated monomer content >20 mol%. The proton conductivity of the polymer membranes depended on the bound water and free water in the membrane, but their methanol permeability depended on the free water content. The maximum selectivity (i.e. proton conductivity/methanol permeability) of the membranes was obtained near the percolation concentration. The behavior of the proton and methanol transport mechanism is discussed in relation to the state of water in the membranes.

Poly(imide siloxane) (PIS) precursors have been synthesized in different compositions and appraised in their ability to form carbon membranes containing silica (C–SiO 2 ). During inert pyrolysis, the imide domains in the PIS were transformed into a carbon-rich phase conferring a molecular sieving capability for molecular pairs of small gases, such as H 2 /N 2 , He/N 2 , CO 2 /N 2 , and O 2 /N 2 . The siloxane domains in the PIS were converted into a silica-rich phase, which provided further gas pathways. The siloxane chain length in the PIS influenced the gas permeation characteristics of the C–SiO 2 membranes. A change in the siloxane chain length of the polydimethylsiloxane (PDMS) segment in the PIS precursor directly influenced the gas permeation and separation properties of the C–SiO 2 membranes. For a constant volume fraction of PDMS moieties, a longer siloxane chain in the PIS led to a drastic increase in gas permeability and a reduction in gas selectivity of the C–SiO 2 membranes. Moreover, the diffusion coefficients of selected gases were also affected by the silica phase, which was embedded in the continuous carbon matrix. The contribution of mobility (diffusion) selectivity to the overall selectivity decreased with volume fraction of PDMS moieties in the PIS precursor. Mixed gas separation experiments were conducted at 25 °C and at a feed pressure of 5 atm (1 atm = 101325 Pa) using feed gas mixtures, such as O 2 /N 2 (71%/29%) and CO 2 /N 2 (15%/85%). For mixed gas separation, carbon-coated microporous alumina tubes were fabricated by dip-coating alumina tubes into siloxane-containing poly(amic acid) (SPA) solutions followed by pyrolysis at temperatures up to 600 °C. The separation properties of the composite membranes showed good agreement with the results obtained from single pure gas permeation experiments.

Imide-siloxane block copolymer/silica hybrid membranes with covalent bonds were prepared via sol–gel reaction. Thestructural informations of these hybrid membranes were obtained by using Fourier transform-infrared spectrometry (FT-IR), 29 Si nuclear magnetic resonance ( 29 Si NMR), XPS and thermogravimetric analysis (TGA). The gas separation properties ofthe hybrid membranes were also investigated in terms of organosiloxane (PDMS) or silica content at various temperatures. Inthe hybrids, the addition of PDMS phase increased the permeabilities of gases such as He, CO 2 ,O 2 , and N 2 , indicating thatthe gas transport occurred mainly through rubbery organic matrix. Meanwhile, the PDMS phase contributed the decreasedgas selectivities to nitrogen but the reduction in selectivities was very small in comparison with other siloxane containingpolymeric membranes. This might be due to the restriction of chain mobility by the existence of inorganic component suchas silica network in the hybrids. Additionally, the increase of silica content in these hybrid membranes considerably retardedthe falling-off of gas selectivity at elevated temperature. The increase of silica content in hybrid membranes resulted inwell-formed silica networks and hence these inorganic components restricted the plasticization of organic matrix by thethermal segmental motion of organic components, leading to preventing the large decrease of the gas selectivity.© 2003 Elsevier B.V. All rights reserved.

Pore-filling concept was applied to prepare high permselective composite membranes for CO2 separation. The membrane is composed of two polymeric materials: a porous substrate and filling polymers that fills the pore of the substrate. In this study, asymmetric polyacrylonitrile (PAN) membrane was used for a substrate and methoxy poly(ethylene glycol) acrylate (MePEGA, Mw=454) was used for a photoinitiated graft polymer. The analysis of graft membrane by Fourier transform infrared and attenuated total reflection (FT-IR, FT-IR/ATR), electron spectroscopy for chemical analysis (ESCA) and field emission scanning electron microphotography (FE-SEM) revealed that the graft polymer filled the pores of the substrate. High CO2/N2 permselectivity was shown by this pore-filling membrane: carbon dioxide permeation flux, J CO 2 =5.65 GPU (10−6 cm3(STP)/cm2 s cmHg) and selectivity of CO2 over N2, JCO2/JN2=32.4 at 30°C, measured by the time-lag method. The high permselectivity of the present pore-filling membrane is attributed to the high solubility selectivity due to the affinity of CO2 to PEO segment.

Poly(acrylonitrile) (PAN)-based co-polymers containing phosphoric acid moiety were synthesized for the dehydration of aqueous pyridine solution. The in situ complex, formed between the phosphoric acid moiety in the membrane and the pyridine in the feed, enhanced the separation capacity of poly(acrylonitrile-co-monoacryloxyethyl phosphate) (PANPH) membranes. All the PAN-based phosphoric acid containing membranes were very selective towards water. The pervaporation performance depended on the content of the phosphoric acid moiety in the membrane, operating temperature, and feed concentrations. The pervaporation separation of water–pyridine mixtures using PANPH membranes exhibited over 97% water concentration in the permeate and a flux of 6–132 g m −2 h −1 , depending on the content of MAEP and the operating temperature.

Polyaniline (PANi) was synthesized by oxidative polymerization and doped with poly(acrylic acid) (PAAc) for pervaporation of aqueous isopropanol. PANi membranes were prepared by solution blending with N -methyl pyrrolidone (NMP) and exhibited the high oxidation stability enough to adopt as dehydration membranes. The conformational hindrance and bulkiness of PAAc chains caused PANi membranes disordered structures. The d-spacings of PANi/PAAc indicated a strong interaction between these two polymers by complexation. When the content of PAAc in doped membrane was 20 wt%, water concentration in permeate decreased to 97 wt%, while permeate flux increased to ca. 200 g/m 2 h due to the affinity of PAAc toward water. Water flux of PANi/PAAc membrane increased with PAAc mixing ratio of up to 30 wt%. Membranes containing more than 30 wt% PAAc showed the analogous results that flux and water concentration in permeate were about 300 g/m 2 h and ∼100 wt%, respectively. Permeate flux through PANi/PAAc membrane decreased with increasing feed IPA concentration while water concentration in permeate was maintained to be over 85 wt%. Water concentration in permeate was much higher than IPA concentration because of high affinity of PANi complex membrane toward water molecules. The activation energy for permeation from an Arrhenius-type expression was ca. 50 KJ/mol.

We investigated the efficiency of pervaporation separation of methanol/methyl-t-butyl ether (MTBE) mixture through chitosan composite membrane modified with sulfuric acid and four surfactants. Effects of feed concentration, temperature, crosslinking degree and type of surfactants were studied. The chitosan composite membrane modified with sulfuric acid showed the pervaporation performance of over 70 wt% methanol in the permeate and flux of 100 g/m2 h measured at 25°C. At 50°C, the separation factor decreased while the flux increased exceeding 300 g/m2 h. For the membrane complexed with surfactants, the permeate showed 98.3 wt% methanol concentration and 470 g/m2 h of permeate flux at 25°C. With increasing operating temperature, the permeate flux remarkably increased to 1170 g/m2 h and the permeate showed 97.8 wt% methanol concentrations.

An ionically surface crosslinked chitosan composite membrane was prepared for pervaporation of ethylene glycol–water mixture. Chitosan membranes exhibited an optimum dehydration performance from ethylene glycol (EG)–water mixtures at 80 min crosslinking time. At 80°C and 80 wt% feed EG concentration, permeation flux of 1130 g/m2 h and water concentration of permeate greater than 99.5 wt% were achieved. Effects of operational conditions including feed EG concentration, operating temperature, and annealing temperature of chitosan membranes on the pervaporation performances of chitosan composite membranes were investigated. At EG concentrations from 70 to 95 wt%, water concentration was higher than EG concentration in the permeate and permeation flux decreased with increasing feed EG concentrations. Annealing of chitosan composite membranes reduced the permeation flux and separation performance of chitosan composite membranes. At high EG concentration in the feed mixture, the membrane was more sensitive to operating temperatures and had higher activation energy of permeation. Water selective chitosan membranes can be applied to evaporation–pervaporation hybrid system for dehydration in the recycle of anti-freezing agent and EG production process.

Chitosan composite membranes were prepared by casting solution onto a porous polyethersulfone ultrafiltration membrane with various surface crosslinking densities. Pervaporation performance of water-alcohol mixtures through the surface crosslinked chitosan composite membranes exhibited a high selectivity value with a low permeation flux. By increasing feed ethanol concentration, permeate flux decreased and water concentration in the permeate decreased drastically at a feed ethanol concentration above 97 wt%. Permeation rate of chitosan composite membranes is less temperature-dependent than that of PVA. IPA-water mixture has a similar tendency as that of ethanol-water mixture in pervaporative dehydration performances.