Mosaic Membranes and Piezodialysis

Miyaki and Fujimoto and co-workers [16,17] have obtained an even finer distribution of fixed charge groups by casting films from multicomponent block copolymers such as poly(isoprene- -styrene- -butadiene- -(4-vinyl benzyl)dime-thylamine- Msoprene). These films show a very regular domain structure with a 200-500 A spacing. After casting the polymer film, the (4-vinyl benzyl) dimethy-lamine blocks were quatemarized with methyl iodide vapor, and the styrene blocks were sulfonated with chlorosulfuric acid. 

Using the block copolymer membranes described above, significant selectivi-ties for electrolytes over non-electrolytes have been observed. Some data reported by Hirahara el al. [17] are shown in Table 13.1. The ionizable electrolytes were 100 times more permeable than non-ionized solutes such as glucose and sucrose, suggesting a number of potential applications in which deionization of mixed solutions is desirable. The permeabilities of salts in these membranes are also 

A second potential application is pressure-driven desalination. When a pressure difference is applied across the membrane, the concentrated ionic groups in the ion exchange domains are swept through the membrane, producing a salt-enriched permeate on the low-pressure side. This process, usually called piezodialysis, has a number of conceptual advantages over the alternative, conventional reverse osmosis, because the minor component (salt), not the major component (water), permeates the membrane. 

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