The Sol-Gel Transition and the Liquid-Liquid Phase Separation in Poly(vinyl chloride) Solutions

Abstract

The dynamics of the sol-gel transition in poly(vinyl chloride) γ-butyrolactone system was investigated by light scattering. The dynamical studies confirmed that this system has an UCST (upper critical solution temperature). In the phase diagram, temperature vs. concentration, the spinodal curve crosses the sol-gel transition curve. This situation has been predicted by Coniglio et al. as a result of the site-bond correlated-percolation problem. The gelation takes place both above and under the spinodal curve, suggesting two modes of gelation: one is accompanied by a spinodal decomposition and the other takes place without liquid-liquid phase separation. In the former case, the dynamics of phase separation at an early stage of gelation is well described within the framework of Cahn’s linearized spinodal decomposition theory. It is noted that, in order to understand the entire mechanism of sol-gel transition, one should clarify the three dynamical aspects on the liquid-liquid phase separation, percolation-type association, and liquid-solid transition.