Study of the structure of asymmetric cellulose acetate membranes for reverse osmosis using electron spin resonance (ESR) method

Electron spin resonance (ESR) technique was used to study the structure of the skin layer of asymmetric cellulose acetate membranes for reverse osmosi s. TEMPO (2,2,6,6-tetramethyl-1-piperridinyloxy-free radical) was used as a spin probe that was brought into the membranes either by reverse osmosis e xperiments with feed solutions involving TEMPO, or by blending TEMPO into c asting solutions. It was found that the mobility of TEMPO in the asymmetric membrane shrunk at 90 degreesC was the same as TEMPO in a dense homogeneou s membrane prepared from the same casting solution as that used for the pre paration of the asymmetric membranes. On the other hand, TEMPO was more mob ile in the asymmetric membranes when they were shrunk at lower temperatures and less mobile in a dense homogeneous membrane when the latter is prepare d from a casting solution without pore former (magnesium perchlorate and wa ter). Reverse osmosis experiments were also performed using feed aqueous so lutions of sodium chloride and/or TEMPO. (C) 2001 Elsevier Science Ltd. All rights reserved.