ATR-FTIR spectroscopic studies of the structure and permeability of sulfonated poly(ether sulfone) membranes .3. Effects of sorption and desorption, and of annealing

The diffusion of water into SPEES/PES polysulfone thin films, with different degrees of sulfonation, has been studied in situ using the FTIR-ATR (attenuated total reflection) technique. Both sorption and desorption processes have been modelled using dual-mode formalism, in order to examine differences in water uptake and retention as a function of cycling in an aqueous ambient. It has been found that, although the sorption kinetics are not dramatically affected by cycling, the desorption process is considerably slowed, to an extent which depends on the sulfonation level. This is particularly true for the third sorption, which also consistently leads to a lower uptake of water. Annealing of the films at temperatures up to 95 degrees C causes a severe reduction in both water uptake and sorption kinetics. These changes have been interpreted in terms of polymer packing density as a function of annealing temperature, and swelling as a function of water content.