A detailed study of the behavior and distribution of water inside ion selective membranes

Water uptake in plasticized polyvinylchloride based ion selective membranes is found to be a two-stage process. In the first stage water is dissolved in the polymer matrix and moves rapidly, with a diffusion coefficient of around 10/sup -6/ cm/sup 2//s. During the second stage a phase transformation occurs that is probably water droplet formation. Transport at this stage shows an apparent diffusion coefficient of 2*10/sup -8/ cm/sup 2//s at short times, but this value changes with time and membrane additives in a complex fashion. The results show clear evidence of stress in the membranes due to water uptake, and that a water-rich surface region develops whose thickness depends on the additives. Hydrophilic additives are found to increase the equilibrium water content, but decrease the rate at which uptake occurs.<>