Pd. Hong et Cm. Chou, Phase separation and gelation behaviors in poly(vinylidene fluoride)/tetra(ethylene glycol) dimethyl ether solutions, POLYMER, 41(23), 2000, pp. 8311-8320
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.