Phase separation and gelation behaviors in poly(vinylidene fluoride)/tetra(ethylene glycol) dimethyl ether solutions

In this work, the phase separation and gelation behaviors in poly(vinyliden e fluoride)/tetra(ethylene glycol) dimethyl ether (PVDF/TG) solutions were studied through the time-resolved light scattering and the gelation kinetic analyses. Combination of the phase diagram and the results of gelation kin etics shows that the gelation behaviors in PVDF/TG solutions could be separ ated into three diverse regions. According to the initial thermodynamic con ditions, one can divide the gelation processes into two major parallel reac tions. At the gelation temperature above the spinodal temperature (T > T-s) , the gelation should he virtually independent of phase separation and then the gelation should occur in terms of bimolecular association and pure cry stalline nucleation. When T < T-s, the crystallization and phase separation occur simultaneously and the gelation depends on the kinetic conditions of two competitive processes. Two gel regions could be separated by a kinetic transition concentration, C-trans* which is obtained from various rate-det ermining mechanisms at the gelation temperature below T-s. When the lower c oncentration PVDF solutions undergo spinodal decomposition, the phase separ ation is the rate-determining step on the gelation and is known as diffusio n control. Meanwhile, the nucleation or reaction control is the rate-determ ining step for the higher concentration ones, indicating that the influence of phase separation on the gelation behavior may be weakened when the conc entration is increased beyond C-trans*. (C) 2000 Elsevier Science Ltd. All rights reserved.