Viscometric and Light Scattering Studies on Microgel Formation by γ-Ray Irradiation to Aqueous Oxygen-free Solutions of Poly(vinyl alcohol)

Abstract

The gelation process of aqueous oxygen-free solutions containing poly(vinyl alcohol) (PVA) by γ-ray irradiation was studied as a function of polymer concentration. Dynamic and static light-scattering techniques as well as the usual viscometric method were employed. PVA solutions turned into a bulk gel upon irradiation at high concentrations around 20 g/L, which corresponds to about 10 times that termed the critical concentration. Increases in the intrinsic viscosity ([n]) and hydrodynamic radius (R h ) were observed before the gelation. The bulk gel did not form from diluted PVA solutions (1.6-2.0 g/L) but the solution became turbid due to the formation of microgel particles. In this process, both [n] and R h rapidly increased when increasing the irradiation dose up to a certain level (ca. 0.3 Mrad) at which solution turbidity appeared. When the irradiation was continued over this dose, [n] decreased and R h leveled off. We thus examined the changes in the molecular weight (M w ) and radius of gyration (Rg) and found that R g decreased while M w increased almost linearly. Thus, a decrease in R g /R h from 1.5 to 0.98 was observed in doses > 0.3 Mrad. On the basis of the results obtained, we discussed in detail the mechanism ofmicrogel formation from PVA in its diluted solution by γ-ray irradiation.