Stress Relaxation of Non-electrolytic Thermo-reversible Gels Concentration Dependence of Distribution Function of Relaxation Times. Polyvinyl Alcohol-Glycerin-Water Gels

From a stress relaxation experiment by means of a chainomatic balance relaxometer the stress relaxation curves were obtained for the gel of polyvinyl alcohol-glycerin-water system, which was taken as an example of non-electrolytic thermoreversible gel. Gels of 8.3%, 9.9% and 12.1% were used. The temperature of the samples was changed between about 2°C and 75°C. Master relaxation curves were obtained for each concentration over the range of time, 10−4∼105 hours, using the time temperature superposition principle. According to Alfrey’s approximation, relaxation spectra were calculated. The following results were obtained. 1) The master relaxation curves exhibit a fairly complicated nature on concentration dependence. 2) The logar vs. T–Ts relation obeys approximately the formula by Williams, Landel and Ferry in the range of T–Ts, −40∼0°C, but outside the range deviates fairly from it. 3) The apparent activation energy is 60 kcal./mole, which is nearly kept constant over the temperature- and concentrationrange in the present work. 4) The shift of the relaxation spectrum due to the change of concentration is not uniform over the region of box type. The maximum point in that region shifts upwards and to the longer-time side with increase of concentration.