Facilitated phase transformation of PVDF in its composite with an ionic liquid

The phase transition of poly(vinylidene fluoride) (PVDF) from ?-to ??-phase is hardly accessible, especially for the low-temperature crystallized ?-phase, owing to the diminished thermal energy available for transformation. In this study, the phase transition ability of ?-PVDF is greatly improved in its composites with a typical imidazole ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The enhanced phase transition is achieved by two thermal steps, including the crystallization of ?-phase and subsequent annealing at a higher temperature. The transformed lamellar morphology is dependent on the crystallization temperature of ?-phase, while the phase transition efficiency mainly rests with the annealing temperature. The phase transition is always accompanied by the thermal degradation with elimination of HF, which is significantly accelerated by [BMIM] [PF6]. The introduction of molecular defects and carbon-carbon double bonds probably increase the fraction of planar chain conformation, therefore, enhancing the phase transition efficiency.

Automated summary

This study demonstrates that the use of imidazole ionic liquid in composites greatly improves the phase transition ability of PVDF, leading to enhanced phase transition efficiency. During the phase transition, the transformed lamellar morphology depends on the crystallization temperature, while the phase transition efficiency is mainly influenced by the annealing temperature.