Dynamic‐mechanical behavior of hydrophobic–hydrophilic interpenetrating copolymer networks

Sequential interpenetrating polymer networks (IPNs) were prepared by free‐radical polymerization. One of the components of the IPN was a poly(butyl acrylate) (PBA) network, and the other one was a poly(methyl methacrylate‐co‐hydroxyethyl methacrylate) copolymer network. Dynamic‐mechanical experiments show that the IPNs are phase separated: two main α relaxations occur in all samples, the low temperature one corresponding to the PBA network and that appearing at higher temperature due to the copolymer network. The latter shows a shape analogous to a pure poly(hydroxyethyl methacrylate) (PHEMA) network independently of the copolymer composition. The influence of water absorption on the dynamic‐mechanical spectrum shows that only a small amount of water reaches the butyl acrylate segments. The dependence of the mechanical behavior of the poly(methyl methacrylate‐co‐hydroxyethyl methacrylate) copolymer networks with the copolymer composition has been also analyzed. POLYM. ENG. SCI., 46:930–937, 2006. © 2006 Society of Plastics Engineers     

Kinetic and thermomechanical analysis of hydrophobic–hydrophilic copolymer thermosets synthesized via free‐radical polymerization

The synthesis of a crosslinked copolymer of hydrophobic and hydrophilic monomers, diglycidyl ether of bisphenol A vinyl ester (VE), and 2‐acrylamido 2‐methyl 1‐propane sulfonic acid (AMPS) respectively, is discussed. A methodology for real‐time monitoring of the copolymerization reaction using transmission mode near infrared (NIR) spectroscopy was employed that resolves overlapping peaks associated with the reactive double bonds. The influence of solvent, monomer ratio, and initiator concentration on the kinetic behavior of the system was investigated. The method of Mayo and Lewis was used to provide a qualitative understanding of the microstructure being formed. At low conversions (<15%) and within the compositions of interest, greater VE homopolymerization as compared with AMPS homopolymerization was observed and the product of the reactivity ratios (r_AMPS.r_VE) was close to 0.5, suggesting the formation of a moderately random copolymer structure. Thermo‐mechanical analysis shows large concentrations of AMPS had a plasticizing effect on the network structure. Solvent removal using supercritical carbon dioxide and thermal drying were compared, and the drying technique were shown to have an effect on the glass transition temperature (T_g), with the lowest T_g being 146°C for supercritically dried samples and 121°C for thermally dried systems. Gel permeation chromatography shows that there is a significant fraction of an unbound mobile phase within the network structure that might be acting as a plasticizing agent for the copolymer structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.     

Solute permeation through perfluorocarboxylate membranes

The sorption and permeability of tetraalkylammonium chlorides and alkali chlorides in perfluorocarboxylate membranes were determined. The water content and density of the membranes were found to change with treatment in boiling water and with different tetraalkylammonium cations as counterions for the carboxylate fixed charge. This is attributed to a change in the structure of the membrane matrices. DSC measurements suggested the existence of three distinct phases in the membranes, i.e. a free water phase, a bound water phase, and nonfreezable water. The nonfreezable water was assumed to be in the fluorocarbon phase. The permeability sequence of the tetraalkylammonium chlorides was found to be TEACl > TMACl > TBACl. To interpret the results, a parallel permeation model was proposed.     

Heat‐resistant hydrophobic–oleophobic coatings

Thermally and chemically durable hydrophobic oleophobic coatings, containing different ceramic particles such as SiO₂, SiC, Al₂O₃, which can be alternative instead of Teflon, have been developed and applied on the aluminum substrates by spin‐coating method. Polyimides, which are high‐thermal resistant heteroaromatic polymers, were synthesized, and fluor oligomers were added to these polymers to obtain hydrophobic–oleophobic properties. After coating, Al surface was subjected to Taber‐abrasion, adhesion, corrosion, and thermal tests. The effects of the particle size of ceramic powders, organic matrix, and heat on the coating material were investigated. Coating material was characterized by FTIR spectrophotometer. Surface properties and thermal resistance of the coating materials were investigated by SEM and TGA analyses. After thermal curing, contact angles of these coatings with H₂O and n‐hexadecane were measured. It was observed that coatings like ceramic particles are more resistant against scratch and abrasion than the other coatings. Also, they are harder than coatings, which do not include ceramic particles. It was seen that coatings, containing Fluorolink D10H, have high‐contact angles with water and n‐hexadecane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2386–2392, 2006     

Selective ion permeation through fluorocarbon polymer membrane

Hydrophobic polymers have rarely been used for membrane materials, but ions permeated selectively through a very thin hydrophobic membrane under a pressure gradient. The membrane was prepared by coating fluorocarbon polymer on a Teflon membrane filter. The permeabilities of strongly hydrated hydrophilic ions and hydrophobic ions are high through the membrane, but those of weakly hydrated ions are low. The selectivities were enlarged in the mixed salts solution of a low concentration at a high pressure. For example, the permeability of KCl was 0.077 and that of LiCl was 0.80 at 1 × 10^?4 mol/dm³ and 40 kg/cm². The coupling between volume flux and ion flux was high for strongly hydrated ions, while the diffusion flux derived by a concentration gradient was high for weakly hydrated ions.     

Selective permeation of sour gases through polymeric membranes modified by sulfolanes. I. Study of selective permeation of CO2 through modified polymeric membranes determined on different systems

Several sulfolanes such as 3-methylsulfolane, sulfolane, and 3-sulfolene were tested as modifiers in poly(trimethylsilyl methyl methacrylate) (PTMSMMA) and poly(trimethylsilyl propyne) (PMSP) to improve the selectivity of CO₂. The gas permeabilities for the PTMSMMA-blend membranes containing high 3-methylsulfolane content were determined on a nonvacuum system in which the membranes started to be measured at their steady states at 30°C; those for all the other membranes were determined in a vacuum system in which those membranes were measured after they reached their unsteady states at 30°C. The PTMSMMA-blend membrane containing 40% 3-methylsulfolane was found to give the best separation of CO₂ under the conditions in this study compared to all the PTMSMMA-blend membranes and the others prepared in our work; its ideal separation factors for CO₂ over N₂ were above 40 and its permeability coefficients of CO₂ increased to above 250 Barrer. The modifications of PMSP membranes by impregnating with sulfolane and blending with sulfolene were found to be effective in improving the selectivity for CO₂ over N₂ for the PMSP membrane. The ideal separation factors for CO₂ over N₂ for the modified PMSP membranes impregnated with 30% sulfolane and blended with 25% 3-sulfolene were improved to above 10 and 13, respectively. © 1996 John Wiley & Sons, Inc.     

Selective permeation of carbon dioxide through synthetic polymer membranes having pyridine moiety as a fixed carrier

Sorption and permeation of CO₂ were investigated by using synthetic polymer membranes having pyridine moiety or pyridine–Cu(II) complex group as a fixed carrier. The solubility data for CO₂ were interpreted by the dual sorption model, Henry's law plus Langmuir-type adsorption. The permeation results of CO₂ through the present membranes containing pyridine moiety were analyzed in terms of the partial immobilization model, while the solubilities and permeablities of O₂ and N₂ obeyed Henry's law. Permselectivity of the present membrane for CO₂ was achieved. These results were explained by the acid-base interaction between CO₂ molecules and fixed carrier in the present membrane.     

Modelling of the pervaporative flux through hydrophilic membranes

This work presents a simplified model of wide applicability for the determination of the pervaporation flux through hydrophilic membranes, provided that the adsorption isotherm of the permeating species onto the pervaporation membrane has a linear shape. The model predicts the pervaporation flux as a function of the activity of the penetrant in the liquid phase and the operation temperature. Experimental results obtained working with two polymeric membranes (CMC‐CF‐23 and Pervap 2256) applied to the dehydration of tetrahydrofuran (THF) and to the separation of methanol from alcohol–ether mixtures, respectively, have been satisfactorily correlated and the characterising parameters have been obtained. Furthermore, the model has been also tested against results obtained with two ceramic membranes, Pervap SMS and zeolite NaA, applied to the dehydration of ketonic mixtures and of tetrahydrofuran respectively. Copyright © 2005 Society of Chemical Industry     

Permeation of water through some heterogeneous hydrophilic membranes

The permeation of water through glyceryl methacrylate (2,3-dihydroxypropyl methacrylate) and 2hyphen;hydroxyethyl methacrylate hydrogels was increased by the incorporation of silica fillers. Both the amount of water at equilibrium and the amount of filler in the gel contribute to increase the permeability of these membranes.     

Characteristics of ammonia permeation through porous silica membranes

A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH₃) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H₂ > NH₃ > N₂. These results suggest that, for permeation through silica membranes, the molecular size of NH₃ is larger than that of H₂, despite previous reports that the kinetic diameter of NH₃ is smaller than that of H₂. At high temperatures, there was no effect of NH₃ adsorption on H₂ permeation characteristics, and silica membranes were highly stable in NH₃ at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH₃ molecules adsorbed on the silica improved NH₃‐permselectivity by blocking permeation of H₂ molecules without decreasing NH₃ permeance. The maximal NH₃/H₂ permeance ratio obtained during binary component separation was ～30 with an NH₃ permeance of ～10^?7 mol m^?2 s^?1 Pa^?1 at an H₂ permeation activation energy of ～6 kJ mol^?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Hydrogen permeation through sol–gel-coated iron during galvanostatic charging

One-layer sol–gel silica–zirconia and two-layer silica–zirconia and zirconia coatings were deposited on one side of iron membranes by spin-coating, densified in air and annealed up to 800 °C in vacuum. Hydrogen permeation through the membranes, coated and uncoated, polarised cathodically under galvanostatic control in 0.1 M NaOH solution was studied using the electrochemical permeation technique. During the initial period, the effect of the sol–gel coatings was insignificant. However, the coatings quite efficiently prevented the iron surface become more active to hydrogen entry during a long-lasting cathodic polarisation. In addition, the electrochemical-corrosion behaviour of the coated iron and the effect of the sol–gel coatings on the effective diffusivity of hydrogen in the coated membranes were studied. On the basis of the polarisation curves and the hydrogen permeation data it was proved that the sol–gel coatings blocked the iron surface for the hydrogen evolution reaction and, consequently, for the hydrogen entry into iron. The effective coating coverage was determined by comparison of the hydrogen fluxes permeating the coated and uncoated membranes. Finally the real concentration of hydrogen beneath the uncoated iron sites and the amount of hydrogen stored in a membrane were evaluated.     

Oxygen permeation through Teflon–PFA tubing into flowing helium

The permeability coefficient for oxygen diffusing through a sample of Teflon-PFA tubing has been determined experimentally. The source of the diffusing oxygen was ambient air surrounding a 1.835 m length of PFA tubing. Pressurized high purity helium was directed through the center of the PFA tubing. Oxygen permeating from the low pressure ambient air source, through the PFA tubing, and into the flowing pressurized helium was observed in the effluent gases as they passed through a trace oxygen analyzer. By this means, oxygen concentrations in the effluent helium were determined as a function of varying helium flow rates, at helium gas pressures of 1.92 and 4.40 atm (absolute), within the tubing bore. All measurements were carried out at ambient temperatures of 23.5 ± 1.3°C. In addition, a theoretically related graphical method of evaluating the experimental data was employed to actually determine the oxygen permeability coefficient for this system.     

A novel model equation for the permeation of hydrogen in mixture with carbon monoxide through Pd–Ag membranes

Hydrogen permeance decrease, owing to the covalent interaction of carbon monoxide with the Pd–Ag membrane surface, represents a considerable drawback, since this decreases the efficiency of the alloy membranes. This work proposes a novel Sieverts–Langmuir's model taking into account the mentioned adsorption. The proposed model equation, in order to take into account the fraction of the membrane surface not active for hydrogen permeation, introduces Langmuir's isotherm, which is the surface loading in the classical Sieverts’ permeation equation. The evaluation of the parameter and the Langmuir affinity constant involved in the proposed model was carried out using experimental data measured using a 60 μm thick Pd–Ag commercial membrane at 647 K (374 °C), up to a total pressure of 700 kPa. The presented model yields, in a parametric form, a quantitative assessment of hydrogen permeance decrease caused by the adsorption of gases on Pd–Ag membrane surfaces. Therefore, this novel Sieverts–Langmuir's equation models hydrogen permeation through Pd–Ag-based membranes in the presence of inhibitor gases such as CO. In addition, by ab initio evaluation of the and the Langmuir affinity constant, the proposed Sieverts–Langmuir's equation can identify a new membrane with better efficiency.     

Effect of metal‐support interface on hydrogen permeation through palladium membranes

Thin palladium membranes of different thicknesses were prepared on sol‐gel derived mesoporous γ‐alumina/α‐alumina and yttria‐stabilized zirconia/α‐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/γ‐Al₂O₃/α‐Al₂O₃ membranes are significantly smaller than those for the Pd/YSZ/α‐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/γ‐Al₂O₃/α‐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/α‐Al₂O₃ membranes. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Preparation of thermosensitive cellophane-graft-N-isopropylacrylamide copolymer membranes and permeation of solutes through the membranes

Thermosensitive membranes with high mechanical strength were prepared by heterogeneous graft copolymerization of N-isopropylacrylamide (NIPAAm) onto cellophane in a nitric acid solution using cerium ammonium nitrate as an initiator, and the permeation behavior of solutes such as lithium chloride and poly(ethylene glycol)s (PEGs) through the membranes at various temperatures was investigated. The degree of graft copolymerization of NIPAAm on cellophane depended on temperature, time, initiator concentration, and so on. The copolymer membranes having a high content of the NIPAAm moiety could be obtained at 25°C for 24 h. The permeation of Li⁺ through the membranes was affected by temperature, i.e., the permeation rate of Li⁺ increased with increasing temperature up to 32°C and then decreased rapidly above 35°C. The permeation rate of Li⁺ through the copolymer membranes at 40°C decreased considerably, but that at 20°C decreased slightly with an increasing amount of the NIPAAm moiety in the membranes. The permeation rate of PEGs with a molecular weight more than 1000 through the cellophane-g-NIPPAm copolymer membranes was considerably suppressed and only the permeation rate of PEG300 increased with increasing temperature up to 35°C and then decreased at 40°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 209–216, 1997     

On the permeation rate of copper extraction through liquid membranes

The understanding of the permeation rate of metal ions through liquid membranes is important for the design of such systems. In this paper, the permeation rates of copper ions through liquid surfactant membranes, including interfacial reaction rates and the diffusion rate of the copper ion, were analyzed using a model based on a mobilized hollow spherical globule configuration. The analysis shows that the extracting reaction is dominant at the external interface of the membrane and the stripping reaction is dominant at the internal interface; this means the reactions at both interfaces are not in equilibrium during the course of extraction. It also shows that the extraction rate, the diffusion rate and the stripping rate are not of equal value, especially at the early stage of the run.