Flow-Induced Crystallization of Crosslinked Poly(vinylidene fluoride) at Elevated Temperatures: Formation and Evolution of the Electroactive β-Phase

Abstract

Flow-induced crystallization of poly(vinylidene fluoride) (PVDF) was investigated for a broad temperature range from 160 to 220 °C by in situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Unexpectedly, the electroactive β-phase is obtained directly from the melt with an extensional flow at 160-200 °C, which is in contrary to the quiescent crystallization of generating the pure α-phase. For 220 °C, the observation of an equatorial SAXS streak without WAXD signals indicates the generation of fibrillar shish. Second, within the isothermal process after flow, the evolution of the flow-induced structure exhibits a strong temperature dependence. The generated β-phase triggers subsequent crystallite growth at 160-180 °C. However, at 190-220 °C, flow-induced fibrillar shish relaxes partially. Third, cooling triggers the crystallization of the α-phase, which competes with the β-phase to determine the final phase constitute. This work reveals the detailed formation and evolution processes of the flow-induced β-phase, which provides an effective approach to obtain the electroactive PVDF materials.