DEPOLARIZATION THERMOCURRENT STUDIES IN POLY(HYDROXYETHYL ACRYLATE) WATER HYDROGELS

Detailed investigations on the dielectric relaxation mechanisms in pol y(hydroxyethyl acrylate) (PHEA), by means of the thermally stimulated depolarization currents (TSDC) method in the temperature range 77-300 K are reported. There is particular interest in the dependence of the dielectric relaxation mechanisms on the water content h, h = 0 - 0.5 w /w, in an attempt to contribute to a better understanding of the physi cal structure of water in the PHEA hydrogels. We employ thermal sampli ng (TS) and partial heating (PH) techniques to experimentally analyze the observed complex relaxation processes, due to the secondary (beta( sw)) and the main (alpha) relaxation, into approximately single respon ses and to determine the spectra of activation energies E(T) at differ ent h values. Measurements with different electrode configurations rev eal different aspects of the dynamics of the relaxation mechanisms and allow the distinction between dipolar and conductivity relaxation con tributions. It is shown that by means of these techniques we can deter mine certain temperature characteristics for the alpha relaxation and investigate their dependence on water content. We discuss the relation of these characteristic temperatures to the calorimetric glass transi tion temperature T(g). (C) 1994 John Wiley & Sons, Inc.