Dielectric studies of molecular mobility in hydrogels

Abstract

We report on polymer–water interactions and on the organization of water in two hydrogel systems, investigated by dielectric relaxation spectroscopy (DRS) measurements. The hydrogels are based on poly(hydroxyethyl acrylate) (PHEA) and on polyacrylamide (PAM), respectively. The water content was systematically varied up to 0.46 g water/g dry material in the PHEA hydrogels and up to 1.5 g/g in the PAM hydrogels. The measuring techniques include broadband DRS in the 5 Hz to 20 GHz frequency range and thermally stimulated depolarization currents (TSDC) techniques in the 77–300 K temperature range. Information on specific polymer–water interactions and on the organization of water in a separate water phase in the pores of the hydrogels is obtained by systematically investigating the effects induced by water on the secondary and main dielectric relaxation mechanisms and on DC conductivity and by looking at the reorientation of water molecules themselves. The PHEA hydrogels were studied extensively, whereas only preliminary results are reported for the PAM hydrogels.