http://worldcat.org/entity/work/id/3558706

Mosaic Membranes for Desalination

Charge mosaic membranes are amphoteric membranes of composite structure, i.e., these membranes consist of small regions of anion selective material interspersed with small regions of cation selective material. In order to be useful in piezodialysis, each ionic region has to extend substantially uniformly from one surface of the membrane to the other one. For practical application the membranes must possess sufficient mechanical strength to withstand pressures up to 1600 psi. Three different approaches were investigated in the preparation of charge mosaic membranes, all of them being based on the incompatibility of different polymers. In the first approach phase separation in block copolymer films composed of styrene and vinyl pyridine was utilized. Films with regularly arranged phases were obtained which could be chemically transformed into cationic and anionic domains. The smallness of the domains (average domain width of the order of several hundred Angstroms) prevented them to extend undisturbed through the film thickness. Piezodialysis effects were not observed with these membranes in their amphoteric state, very likely for two reasons, improper film morphology and formation of extended regions of poly-poly salts on the boundaries between the anionic and cationic domains. jg p9.

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