The formation of phase inversion membranes made by immersion precipitation from a ternary system consisting of an amorphous polymer, a solvent, and a nonsolvent has been rationalized by assuming a gelation process. The treatise is based on a hypothesis developed by Berghmans for a binary system consisting of a polymer and a solvent. The ternary phase diagram for the mixture of H2O−NMP (N-methylpyrrolidone)−PES (poly(ether sulfone)) was determined at 25 °C. In this system three boundaries could be identified, i.e., a vitrification, a gelation, and a binodal boundary. It was found that for this system and a system composed of H2O−DMAC (N,N-dimethylacetamide)−PSF (polysulfone), vitrification is the only mechanism responsible for the structure fixation of membranes prepared by liquid−liquid demixing due to immersion precipitation. For the system of MPD (2-methyl-2,4-pentanediol)−NMP−PES, it was found that a membrane can be formed by vitrification as a result of immersion precipitation prior to liquid−liquid demixing. The depressions of the glass transition temperature of PES by the addition of FP (N-formylpiperidine), DMSO (dimethyl sulfoxide), DMAC, or NMP as well as by a mixture of NMP and water are determined.
In this paper tailor‐made polymers like polyoxadiazoles, polytriazoles and polyimides are compared with conventional polymers as gas separation membrane materials. Because their permeation characteristics as a function of the free volume does not compare too well with that of the conventional ones the term free volume was reconsidered. Based on a unique relation between the diffusion coefficient and the jump of the heat capacity at the glass transition temperature Tg, the transport mechanism in the polymer matrix is considered to occur in jump motions from one cavity to an adjacent one. This mechanism was reconfirmed by a molecular dynamics study. It is shown that mass transport at high penetrant concentrations is not time‐independent but a phenomenon with transient characteristics. This transient character is also found in the volumetric behaviour during sorption. The polymer matrix is described as a network with topological constraints which changes its state upon high swelling stresses induced by the sorbed penetrant.
The meetmg was orgamsed on the occasion of the retirement of professor dr. C.A Smolders, who has directed the Membrane Technology group at the Umversity of Twente for 23 years The purpose of this meeting was to present a collection of papers on past achievements m membrane science, but mainly to enable enthusiastic membrane technologists to discuss the current state and future of this rapidly developing field of separation technology The broadness of the field can be Judged from the variety of papers which have been presented, ranging from the formation of macrovoids and nodules (Smolders et al) to the development of modules (Knops et al) and from the fundamentals of mass transport through membranes (Wesselmgh) to membrane apphcations (Banduu et al , Bleha et al and Kreulen et al) With its ca 250 participants from 26 countries the conference hosted a very competent audience which contributed to the success of the symposium This is one of mam reasons to organize a follow up m 1994 (June 2%July 1) The orgamzers would hke to thank all participants for their contributions and the authors for the preparation of the manuscripts which are now available m this special issue Finally I would hke to wish all the best to Kees and Leny Smolders THONIE VAN DEN BOOMGAARD
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