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 γ 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 γ PVDF due to the existence of strong ion-dipole interactions. Five stages are identified and intensive information on the growth and phase transition of α and γ phases in each stage is offered. Specifically, an induction periods observed for both α and γ phases in the stage I. In stage II, the α phase is initiated while the γ phase is still in the induction period, i.e., the nucleation and development of α phase are prior to the γ phase, although the resultant sample presents exclusively pure γ phase. The nucleation effect of CTAB for the γ phase is triggered in stage III, but α phase still grows faster than that of γ phase. Incorporating more CTAB impedes the growth of α phase while accelerates the development of γ phase. In stage IV, an α–γ phase solid transition accompanies the melt crystallization of the γ phase, and the α–γ phase transition is accelerated by CTAB molecules dramatically. Finally, the melt crystallization of the γ phase is completed, only α–γ phase transition is observed. This effort indicates that the pure γ 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.