Swelling/shrinking kinetics of chemically cross-linked poly(vinyl alcohol) gels in the presence of borate ions

The swelling/shrinking kinetics of chemically cross-linked poly(vinyl alcohol) (PVA) gels with borate ions has been studied by measuring the gel size as a function of time. The experimental process consisted of two steps, i.e., (I) immersion of a gel in a mixture of NaOH and boric acid aqueous solutions. and (II) subsequent immersion in deionized water or in a NaOH solution without borate ions. In step I, the gel swelled or shrank depending on the borate ion concentration and reached individual equilibrium values within 5000 min. After equilibration, the gel was transferred to the second bath and step Il was initiated. When a gel was immersed in deionized water, the gel swelled considerably and then deswelled gradually to the original size. On the other hand, when a gel was dipped in a bath containing NaOH, a reverse process of step I took place and the gel size gradually reduced to the original size. The diffusion coefficients in these steps are discussed in conjunction with those obtained by dynamic light scattering. (C) 1996 American Institute of Physics.