Water vapor sorption in naphthalenic sulfonated polyimide membranes

The water vapor uptake of sulfonated polyimides (SP) was investigated by el ectronic microbalance (IGA, Hiden) from 15 to 55 degreesC. The sigmoidal is otherms obtained (BET II type) are considered as dual sorption (concave par t) plus clustering (convex part) and are fitted with good agreement by Park 's equation, Zimm-Lundberg's method is used to study the clustering process of water molecules limit clustering activity, alpha*, and the number of mo lecules per cluster are estimated. To obtain a better understanding of polymer structure and isotherm analysis , H+ (counter-ions of sulfonic groups) were replaced by ions with a smaller hydration shell (Cs+ and EDAH(+)). Comparison of the three isotherms shows no significant difference in the water affinity of the cations. This is at tributed to a partial control of the sorption by microcavities existing in the membrane. (C) 2001 Elsevier Science B.V. All rights reserved.