Home About us Contact
|
Home About us Contact | ||
|
|
||
Asymmetric Membranes (asymmetric + membrane)
Selected AbstractsSelf-Supporting, Double Stimuli-Responsive Porous Membranes From Polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) Diblock CopolymersADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Felix Schacher Abstract Asymmetric membranes are prepared via the non-solvent-induced phase separation (NIPS) process from a polystyrene- block -poly(N,N -dimethylaminoethyl methacrylate) (PS- b -PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100,nm on top and a macroporous volume structure, the membranes are self-supporting. Furthermore, they exhibit a defect-free surface over several 100,µm2. Polystyrene serves as the membrane matrix, whereas the pH- and temperature-sensitive minority block, PDMAEMA, renders the material double stimuli-responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven-fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH-dependent filtration of silica particles with sizes of 12,100,nm. [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] Gas transport properties of asymmetric polyimide membranes prepared by plasma-based ion implantationPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2009Teppei Tezuka Abstract In this study, we report the gas permeance and selectivity of the asymmetric polyimide membrane prepared by plasma-based ion implantation (PBII). The asymmetric polyimide membranes were prepared using a dry,wet phase inversion process, and the surface skin layer on the membrane was implantated by He ions at 2.5,keV. The asymmetric membranes treated by PBII were measured using a high vacuum apparatus with a Baratron absolute pressure gauge at 76,cmHg and 35°C. The (O2/N2) and (CO2/CH4) selectivities in the He+ -implanted asymmetric membrane at 60,sec resulted in 1.5 and 1.8 time increases, respectively, when compared to those of the asymmetric membrane before PBII. On the other hand, the O2 and CO2 permeances in the asymmetric membrane after PBII decreased with an increase in the He+ treatment time. In this paper, we addressed, for the first time, the gas permeation behavior of the asymmetric polyimide membranes prepared by PBII. Copyright © 2009 John Wiley & Sons, Ltd. [source] Tailoring Macromolecular Expression at Polymersome SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Adam Blanazs Abstract A series of amphiphilic ABC triblock copolymers are synthesized by atom transfer radical polymerization, wherein the ,A' and ,C' blocks are hydrophilic and the pH-sensitive ,B' block can be switched from hydrophilic in acidic solution to hydrophobic at pH 7. Careful addition of base to the molecularly dissolved copolymer in acidic solution readily induces the self-assembly of such triblock copolymers at around neutral pH to form pH-sensitive polymersomes (a.k.a. vesicles) with asymmetric membranes. By systematic variation of the relative volume fractions of the ,A' and ,C' blocks, the chemical nature of the polymer chains expressed at the interior or exterior corona of the polymersomes can be selected. Treatment of primary human dermal fibroblast cells with these asymmetric polymersomes demonstrates the biological consequences of such spatial segregation, with both polymersome cytotoxicity and endocytosis rates being dictated by the nature of the polymersome surface chemistry. The pH-sensitive nature of the polymersomes readily facilitates their dissociation after endocytosis due to the relatively low endosomal pH, which results in the rapid release of an encapsulated dye. Selective binding of anionic substrates such as DNA within the inner cationic polymersome volume, coupled with a biocompatible exterior, leads to potential gene delivery applications for these pH-sensitive asymmetric nanovectors. [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] Semi-IPN asymmetric membranes based on polyether imide (ULTEM) and polyethylene glycol diacrylate for gaseous separationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Sundar Saimani Abstract Semi-interpenetrating polymer networks (semi-IPN) formed with commercial polyether imide (ULTEM®, PEI) and poly (ethylene glycol) diacrylate (PEGDA) were used to make asymmetric membranes. The effect of increasing amount of PEGDA on the bulk and the gas separation properties of semi-IPN membranes were studied. The formation of IPNs was confirmed by Fourier Transform Infra Red (FT-IR) spectroscopy. The 5% weight loss temperature decreased and the percent weight loss of the first step increased with increase in the PEGDA content, which indicated the incorporation of more poly (ethylene glycol) (PEG) segments to the semi-IPNs. The microscopic experiments revealed the change in morphology with change in PEGDA content. The Scanning electron micrographs exhibited typical finger-like voids in the sub layer, which is characteristic morphology of asymmetric membranes. The increase in PEGDA content up to 5.7 wt % increased the CO2/N2 selectivity of the semi-IPN after which the selectivity decreased and permeance increased. Although, the increase in the polar poly (ethylene glycol) molecules is expected to render better CO2 selectivity, the performance of the membrane was found to decrease as PEGDA content exceeded 5.7% for the given ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] A New Numerical Approach for a Detailed Multicomponent Gas Separation Membrane Model and AspenPlus SimulationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2005M. H. Murad Chowdhury Abstract A new numerical solution approach for a widely accepted model developed earlier by Pan [1] for multicomponent gas separation by high-flux asymmetric membranes is presented. The advantage of the new technique is that it can easily be incorporated into commercial process simulators such as AspenPlusTM [2] as a user-model for an overall membrane process study and for the design and simulation of hybrid processes (i.e., membrane plus chemical absorption or membrane plus physical absorption). The proposed technique does not require initial estimates of the pressure, flow and concentration profiles inside the fiber as does in Pan's original approach, thus allowing faster execution of the model equations. The numerical solution was formulated as an initial value problem (IVP). Either Adams-Moulton's or Gear's backward differentiation formulas (BDF) method was used for solving the non-linear differential equations, and a modified Powell hybrid algorithm with a finite-difference approximation of the Jacobian was used to solve the non-linear algebraic equations. The model predictions were validated with experimental data reported in the literature for different types of membrane gas separation systems with or without purge streams. The robustness of the new numerical technique was also tested by simulating the stiff type of problems such as air dehydration. This demonstrates the potential of the new solution technique to handle different membrane systems conveniently. As an illustration, a multi-stage membrane plant with recycle and purge streams has been designed and simulated for CO2 capture from a 500,MW power plant flue gas as a first step to build hybrid processes and also to make an economic comparison among different existing separation technologies available for CO2 separation from flue gas. [source] | ||||||||||