The Transient Response of the Swelling in Mixed Solvent for the Freeze/Thawed Polyacrylonitrile Gel Observed in Association with the Polymer Elution

Abstract

The swelling properties of polyacrylonitrile gel prepared by the repeating cycle of freezing and thawing were examined, as its transient response toward the equilibrium swollen states varies with the variation of mixing ratio (r) of the immersion solvent which consisted of N, N–dimethylacetamide and benzene. Two experimental protocols were used; successive solvent exchanges were conducted in Protocol 1, and no solvent exchange but the varying of the volume of immersion solvent was conducted in Protocol 2. Also, the aging time was set between the end of the freezing and thawing cycle and the start of the swelling experiment. As a result, the equilibrium swelling ratio decreased with the increase in the aging time. Significant discrepancies for the transient responses were found for the immersion solvents between r ≤ 0.74 and r ≥ 0.78 both in Protocol 1 and 2, in which the elution of polyacrylonitrile molecules was related to the responses. A characteristic overshoot curve was observed in the swelling with r ≥ 0.78 in Protocol 2, which was also attributed to the polyacrylonitrile elution. The polymer solvent interaction parameter was calculated on the basis of the osmotic pressure equilibrium, which was associated with the interpretation of the transient response data.