ION EXCHANGE MEMBRANES

The importance of membranes in physical chemistry as well as in the biological sciences is due to their twofold character. On the one hand, membranes are restrictive barriers which selectively influence the transportation and exchange by diffusion, osmosis or otherwise of the various molecular and ionic species contained in the two compartments which are separated by the membrane. On the other hand, membranes, by virtue of their being barriers, act also as physicochemical machines which regulate the flow of the energetic processes which occur across their thickness; and, in doing this, they transform various forms of energy into others, for instance, osmotic energy into mechanical work or into electrical energy.’ Membranes which are known today to be of ion exchange character have been investigated for many decades by physical chemists, and more extensively by biologists. Virtually all the fundamental electrochemical membrane phenomena were thoroughly described and basically understood before the true underlying physical mechanism, the ion exchange nature of the membranes, was clearly realized. After the ion exchange character of electrochemically active membranes was recognized and extensive theoretical and experimental work started on this new basis, it was more than ten years before membranes prepared from conventional, commercial type ion exchanger material were described. Thus, ion exchangers of the high capacity, commercial type which, after all, are only one special class of a much larger group, are late comers in the membrane field. Up to the present, hardly a single significant, new observation has been made with a membrane prepared from the commercial type of ion exchangers which has not been described earlier and with a higher degree of accuracy. At present, numerous investigators here and abroad, using commercial type ion exchangers, are beginning to study the electrochemistry of membranes, primarily looking for technological applications. There is little doubt in the mind of the author that, in the long run, membranes, prepared with the aid of methods more or less common in ion exchange technology, will assume industrial importance? The current process of merging of the knowledge of electrochemistry of membranes with the vast body of experience in the ion exchanger field is bound to be of great mutual benefit. It is too early at present to predict where the first “big break” from an industrial point of view will come, and in which direction the membrane technology of the future will develop. The main purpose of this paper is not to indulge in speculations along these lines, but rather to present the fundamental aspects of the electrochemistry of membranes of ion exchange character; to indicate the methods of preparing