EXPERIMENTS ON POLYMER GELS - SWELLING AND DEFORMATION OF POLY(VINYL ACETATE) NETWORKS IN EQUILIBRIUM WITH A THETA-DILUENT

Deswelling of chemically cross-linked poly (vinyl acetate) gels swollen by isopropyl alcohol at the θ-temperature (T=52°C) was induced by two independent methods: (1) the activity of the diluent around the stress-free gels was lowered by dissolving a polymer in the equilibrium liquid phase and (2) gels equilibrated with pure diluent were subjected to unidirectional compressive stress. In addition, shear modulus measurements were performed on the gels at different stages of deswelling. The results are described by relationships derived between the swelling pressure, shear modulus, deformation ratio and polymer concentration. The concentration dependence of the shear moduli of poly (vinyl acetate) gel homologues in the fully swollen state exhibits a power-law exponent 2.96, which is close to the theoretical value of 3. It is shown that for gels subjected to unidirectional compressive stress, the difference in chemical potential between the pure diluent and the diluent in the deswollen gel, Δμ1, is given by the equation Δμ1=G(φ) (1 - Λ- 8 9e), where G(φ) is the shear modulus and Λe is the deformation ratio relative to the length of the freely swollen undeformed sample. © 1990.