Temperature-Induced Swelling of Alkali Metal Polyacrylate Gels in Aqueous Organic Solvent Mixtures

Abstract

ABSTRACTIt has been known that some polyelectrolyte systems, e.g., betaine polymer and polycations, have an upper critical solution temperature (UCST) in water while polyanions seldom show such a temperature-dependent phase separation. Recently we have found a significant counterion- and solvent-specific UCST-type behavior for alkali metal poly(acrylate)s (PAAM) in aqueous organic solvent mixtures. Namely, the reduced viscosity significantly increased with increasing temperature which was ascribed to disintegration of the ion-clusters or the aggregated ion-pairs formed at the lower temperature. In the present study, we prepared PAAM gel samples by irradiating the aqueous solutions with γ-rays in variable doses to find that a significant gel swelling was induced by a temperature jump from 5 to 40°C in various kinds of aqueous organic solvent mixtures. The UCST-type behavior and the counterion- and solvent-specificities for the gel swelling turned out to be parallel to those for the corresponding solution systems. In addition to these expected results, an appreciable LCST-type deswelling was unexpectedly observed for collapsed gels in a relatively higher solvent concentration region. Further, the γ-ray doses, i.e., the degree of crosslinking, proved to affect the UCST behavior; the gel swelling ratio was more significant for gels prepared with higher doses.