Dielectric studies of molecular mobility in hydrogels

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 syst ematically varied up to 0.46 g water/g dry material in the PHEA hydrogels a nd up to 1.5 g/g in the PAM hydrogels. The measuring techniques include bro adband DRS in the 5 Hz to 20 GHz frequency range and thermally stimulated d epolarization 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 obtain ed by systematically investigating the effects induced by water on the seco ndary and main dielectric relaxation mechanisms and on DC conductivity and by looking at the reorientation of water molecules themselves. The PHEA hyd rogels were studied extensively, whereas only preliminary results are repor ted for the PAM hydrogels. (C) 1999 Elsevier Science B.V. All rights reserv ed.