Polymer-water interactions in PAA hydrogels

Polymer-water interactions in poyacrylamide (PAA) hydrogels were investigat ed by means of broad-band dielectric relaxation spectroscopy (DRS, 10(-2)-1 0(6) Hz) and of thermally stimulated depolarization currents (TSDC) techniq ues (77-300 K) at several hydration levels. The critical water content for the saturation of primary hydration sites was determined to be h(c)=0.15 (d ry basis). For water contents h>h(c) plasticization effects dominate the be haviour of hydrogels. Two further critical water contents were determined f rom TSDC measurements at subzero temperatures related to freezing of water and to reorganization of water in the hydrogels, respectively. The activati on energy of DC protonic conductivity was determined to be 0.8+/-0.1 eV at h=0.25. (C) 1999 Elsevier Science B.V. All rights reserved.