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

Abstract

In this work, the phase separation and gelation behaviors in poly(vinylidene 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 kinetics shows that the gelation behaviors in PVDF/TG solutions could be separated into three diverse regions. According to the initial thermodynamic conditions, one can divide the gelation processes into two major parallel reactions. At the gelation temperature above the spinodal temperature ( T> T s), the gelation should be virtually independent of phase separation and then the gelation should occur in terms of bimolecular association and pure crystalline 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-determining mechanisms at the gelation temperature below T s. When the lower concentration PVDF solutions undergo spinodal decomposition, the phase separation is the rate-determining step on the gelation and is known as diffusion control. Meanwhile, the nucleation or reaction control is the rate-determining step for the higher concentration ones, indicating that the influence of phase separation on the gelation behavior may be weakened when the concentration is increased beyond C trans ∗.