Multiple stage crystallization of gamma phase poly(vinylidene fluoride) induced by ion-dipole interaction as revealed by time-resolved FTIR and two-dimensional correlation analysis

The polymorphic gamma poly(vinylidene fluoride) (PVDF) induced by an ionic surfactant, cetyltrimethyl ammonium bromide (CTAB), is studied by using time-resolved Fourier transform infrared (FTIR) and two-dimensional (2D) correlation analysis. It is found that an extremely low content of CTAB can effectively induce gamma PVDF due to the existence of strong ion-dipole interactions. Five stages are identified and intensive information on the growth and phase transition of alpha and gamma phases in each stage is offered. Specifically, an induction periods observed for both alpha and gamma phases in the stage I. In stage II, the alpha phase is initiated while the gamma phase is still in the induction period, i.e., the nucleation and development of alpha phase are prior to the gamma phase, although the resultant sample presents exclusively pure gamma phase. The nucleation effect of CTAB for the gamma phase is triggered in stage III, but alpha phase still grows faster than that of gamma phase. Incorporating more CTAB impedes the growth of alpha phase while accelerates the development of gamma phase. In stage IV, an alpha-gamma phase solid transition accompanies the melt crystallization of the gamma phase, and the alpha-gamma phase transition is accelerated by CTAB molecules dramatically. Finally, the melt crystallization of the gamma phase is completed, only alpha-gamma phase transition is observed. This effort indicates that the pure gamma phase of PVDF induced by ion-dipole interactions could originate from multiple phase behaviors, which could be helpful for understanding and manipulation of PVDF polar. phases. (C) 2014 Elsevier Ltd. All rights reserved.