Macromolecules, Vol.27, No.19, 5350-5358, 1994
Swelling Shrinking and Dynamic Light-Scattering-Studies on Chemically Cross-Linked Poly(Vinyl Alcohol) Gels in the Presence of Borate Ions
Swelling/shrinking behaviors of chemically cross-linked poly(vinyl alcohol) (PVA) gel complexed with borate ions were studied as a function of the borate ion concentration, b, and time. The equilibrium swelling ratio, Q/Q0, was compared with the intrinsic viscosity ratio, [eta]/[eta]0, of the corresponding PVA solutions in the presence of borate ions, where Q0 and [eta]0 are the equilibrium swelling volume of the gel and the intrinsic viscosity of the solution without borate ions, respectively. The b dependence of Q/Q0 was almost the same as that of [eta]/[eta]0. From the kinetic measurements of gel swelling and shrinking, the macroscopic diffusion coefficients for swelling and shrinking, D(macro) = D(swell) and D(shrink), respectively, were obtained. It was found that D(shrink) is about a tenth of D(swell). The dynamics of a gel network were also studied by dynamic light scattering, where two types of diffusion coefficients, D(HT) (the heterodyne method) and D(NE) (the nonergodic medium method), were evaluated by coupling the time and ensemble-average intensity correlation functions for swollen gels. It was disclosed that D(swell) is in good agreement with D(HT), not with D(NE). The physical meanings of D(HT) and D(NE) are discussed in connection with the macroscopic diffusion coefficients, D(swell) and D(shrink).