Enhanced αγ′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing
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Poly(vinylidene fluoride) (PVDF) exhibits pronounced polymorphs. Its γ phase is attractive due to the electroactive properties. The γ-PVDF is however difficult to obtain under normal crystallization condition. In a previous work, we reported a simple melt-recrystallization approach for producing γ-phase rich PVDF thin films through selective melting and subsequent recrystallization. We reported here another approach for promoting the αγ′ phase transition to prepare γ-phase rich PVDF thin films. To this end, a stepwise crystallization and subsequent annealing process was used. The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition. It was found that crystallizing the PVDF melt first at 152 °C for 4 h, then quenching to room temperature and finally annealing the sample at 160 °C for 100 h was the most efficient to produce γ-PVDF rich films. This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 °C, which favors the formation of γ-PVDF crystals for triggering the αγ′ phase transition.
KeywordsPoly(vinylidene fluoride) Step crystallization Annealing Phase transition
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