Enhanced solid α- to γ′-phase transition of poly(vinylidene fluoride) via polar nanodomains with high-concentration ionic liquids

Timesaving but efficient fabrication strategy of γ′-poly(vinylidene fluoride) (PVDF) materials is highly demanded for manufacturing PVDF-based electronic devices, yet remains challenging so far. In this work, over 90 % γ′-phase crystals have been obtained in just 50 min in microphase-separated PVDF-co-(PVDF-g-IL) [i.e., the copolymer of PVDF and PVDF grafted with ionic liquid (IL, 1-butyl-3-vinylimidazolium tetrafluoroborate)]. Our results indicate that the PVDF-g-IL nanodomains with high-concentration ILs induced by microphase separation play multiple roles in the fast and high-efficiency solid phase transition of PVDF crystals. Firstly, they produce nucleation effect instead of depression effect on the crystallization of PVDF matrix since all miscible ILs have been restricted in these domains; secondly, the high-concentration ILs in PVDF-g-IL nanodomains facilitates to induce polar conformation of PVDF segments and the consequent γ′-phase PVDF crystals; finally, the solid phase transition can be spread to the whole specimen with the help of widely distributed PVDF-g-IL nanodomains within PVDF matrix, regardless of the thickness of specimen. Our results are significant for not only the fabrication of γ′-PVDF composites, but also the basic understanding of solid α- to γ′-phase transition.