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Permeation Properties (permeation + property)
Selected AbstractsPhotoswitchable Gas Permeation Membranes Based on Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Eric G, owacki Abstract We have fabricated switchable gas permeation membranes in which a photoswitchable low-molecular-weight liquid crystalline (LC) material acts as the active element. Liquid crystal mixtures are doped with mesogenic azo dyes and infused into commercially available track-etched membranes with regular cylindrical pores (0.40 to 10.0 ,m). Tunability of mass transfer can be achieved through a combination of (1) LC/mesogenic dye composition, (2) surface-induced alignment, and (3) reversible photoinduced LC-isotropic transitions. Photo-induced isothermal phase changes in the imbibed material afford large and fully reversible changes in the permeability of the membrane to nitrogen. Both the LC and photogenerated isotropic states demonstrate a linear permeability/pressure relationship, but they show significant differences in their permeability coefficients. Liquid crystal compositions can be chosen such that the LC phase is more permeable than the isotropic,or vice versa , and can be further tuned by surface alignment. Permeability switching response times are 5 s, with alternating UV and >420-nm radiation at an intensity of 2 mW/cm2 being sufficient for complete and reversible switching. Thermal and kinetic properties of the confined LC materials are evaluated and correlated with the observed permeation properties. We demonstrate for the first time reversible permeation control of a membrane with light irradiation. [source] Bilayer localization of membrane-active peptides studied in biomimetic vesicles by visible and fluorescence spectroscopiesFEBS JOURNAL, Issue 22 2003Tanya Sheynis Depth of bilayer penetration and effects on lipid mobility conferred by the membrane-active peptides magainin, melittin, and a hydrophobic helical sequence KKA(LA)7KK (denoted KAL), were investigated by colorimetric and time-resolved fluorescence techniques in biomimetic phospholipid/poly(diacetylene) vesicles. The experiments demonstrated that the extent of bilayer permeation and peptide localization within the membrane was dependent upon the bilayer composition, and that distinct dynamic modifications were induced by each peptide within the head-group environment of the phospholipids. Solvent relaxation, fluorescence correlation spectroscopy and fluorescence quenching analyses, employing probes at different locations within the bilayer, showed that magainin and melittin inserted close to the glycerol residues in bilayers incorporating negatively charged phospholipids, but predominant association at the lipid,water interface occurred in bilayers containing zwitterionic phospholipids. The fluorescence and colorimetric analyses also exposed the different permeation properties and distinct dynamic influence of the peptides: magainin exhibited the most pronounced interfacial attachment onto the vesicles, melittin penetrated more into the bilayers, while the KAL peptide inserted deepest into the hydrophobic core of the lipid assemblies. The solvent relaxation results suggest that decreasing the lipid fluidity might be an important initial factor contributing to the membrane activity of antimicrobial peptides. [source] Structure and gas permeation properties of asymmetric polyimide membranes made by dry,wet phase inversion: Influence of the polyimide molecular weightJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Naoko Seki Abstract In this article, we report the influence of the polyimide molecular weight (1.2 × 105, 2.6 × 105, and 4.1 × 105) on the structure and the gas permeation properties of asymmetric polyimide membranes made by the dry,wet phase-inversion process. The apparent skin layer thickness of the asymmetric membrane increased with increasing molecular weight, and the thicknesses of the membranes prepared from the three polyimides with a casting polymer solution containing 8.0 wt % butanol were 132, 350, and 739 nm, respectively. That is, the gas permeance in the asymmetric membranes increased with decreasing molecular weight. In contrast, the gas selectivity of the asymmetric membranes did not depend on the skin layer thickness. The solvent evaporation in the dry phase-inversion process and the nonsolvent diffusion in the dry process were important factors that determined the formation of the asymmetric membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Impact of H+ ion beam irradiation on Matrimid®.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Abstract Ion beam irradiation is an easily controlled method to modify the chemical structure and microstructure of polymers including the fractional free volume, free volume distribution and chain mobility, thus altering the gas transport properties of the irradiated polymers. The previous paper focused on the impact of H+ ion beam irradiation on chemical structural evolution of the polyimide Matrimid®. This paper focuses on the impact of H+ ion beam irradiation on microstructure and gas permeation properties of Matrimid®. Irradiation at low ion fluence resulted in slight decreases in permeabilities for five gases (i.e., He, CO2, O2, N2, and CH4) with increases in permselectivities for some gas pairs (e.g., He/CH4 and He/N2). In contrast, irradiation at relatively high ion fluences resulted in simultaneous increases in permeabilities and permselectivities for most gas pairs (e.g., He/CH4, He/N2, O2/N2, and CO2/CH4). While Matrimid® has bulk gas permeation properties that are below the range of commercially interesting polymers, samples irradiated at high ion fluences exhibited significant improvement in gas separation performances. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1670,1680, 2007 [source] Effect of metal-support interface on hydrogen permeation through palladium membranesAICHE JOURNAL, Issue 3 2009Ke Zhang Abstract Thin palladium membranes of different thicknesses were prepared on sol-gel derived mesoporous ,-alumina/,-alumina and yttria-stabilized zirconia/,-alumina supports by a method combining sputter deposition and electroless plating. The effect of metal-support interface on hydrogen transport permeation properties was investigated by comparing hydrogen permeation data for these membranes measured under different conditions. Hydrogen permeation fluxes for the Pd/,-Al2O3/,-Al2O3 membranes are significantly smaller than those for the Pd/YSZ/,-Al2O3 membranes under similar conditions. As the palladium membrane thickness increases, the difference in permeation fluxes between these two groups of membranes decreases and the pressure exponent for permeation flux approaches 0.5 from 1. Analysis of the permeation data with a permeation model shows that both groups of membranes have similar hydrogen permeability for bulk diffusion, but the Pd/,-Al2O3/,-Al2O3 membranes exhibit a much lower surface reaction rate constant with higher activation energy, due possibly to the formation of Pd-Al alloy, than the Pd/YSZ/,-Al2O3 membranes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Metal ion permeation properties of silk fibroin/chitosan blend membranesPOLYMER INTERNATIONAL, Issue 4 2006Chun-Hui Du Abstract Silk fibroin/chitosan (SF/CS) blend membranes were prepared and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy. It was found that SF and CS were compatible in the blend membranes and that the membranes were dense without microscopic phase separation. Swelling experiments showed that the swelling ratio of the blend membranes increased with CS content and reached the highest value when CS content was 70 wt%. Experiments indicated that the permeability coefficient of K+ through the blend membrane was 2,4 times higher than that of pure CS membrane, and 10 times higher than that of pure SF membrane. The permeation rate of K+ increased linearly with CS content in the blend membrane for the lower concentration feeding solution. For different metal ions, the permeability through SF/CS blend membranes was in the sequence K+ > Ca2+ > Cd2+ > Pb2+ > Cu2+ > Ni2+. Copyright © 2006 Society of Chemical Industry [source] Gas permeation properties of Seragel membraneASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010M. Saeidi Abstract Gas permeation behavior through a specific type of polymeric membrane was investigated in this work. The main objective of our study was to determine gas permeation properties of a specific polymeric membrane over a range of operating pressures. The diffusive layer of this membrane consists of Butadiene,Sulfone block copolymer and demonstrates high chemical stability in corrosive media. Permeances were determined at the temperature of 35 °C and pressures of 760, 1520, and 3040 cmHg for methane, carbon dioxide, and nitrogen. Gas permeances were also determined for actual binary mixtures of H2S/CH4. Average permeances of 23.17 and 3.75 GPU for H2S and CO2 were achieved respectively, at the pressure range of 380,1140 cmHg. Calculated permeances by a model developed for this membrane in previous literatures have been compared with experimental data in this study and the agreement of the model with H2S/CH4 mixture was also investigated. The results show that the agreement between the pure gas experimental permeances and the data from the model is more in comparison with the experimental gas mixture results. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||