Effect of rolling temperature on the microstructure and electric properties of β-polyvinylidene fluoride films

Abstract

Due to its outstanding dielectric, ferroelectric and piezoelectric properties among polymers, β-poly(vinylidene fluoride) (PVDF) has been widely used in flexible sensors, transducers and energy harvesters. These applications trigged tremendous interest infabrication of β-PVDF films with high electric performance over decades. Herein, the traditional solution casting method combined with a novel low-temperature double rolling approach was developed to fabricate β-PVDF films with superior dielectric, ferroelectric and piezoelectric properties. A systematic investigation was performed to study the effect of rolling temperature on the microstructure and electric properties of original β-PVDF obtained from solution casting. The results showed that rolling at temperatures between 25 and 60 °C could slightly influence the crystal forms of the β-PVDF films, but induce a well-oriented β-phase structure. Moreover, rolling at temperatures below 60 °C can significantly reduce the crystallite size of PVDF. With declined crystallite size, improved chain orientation and morphological continuity along the rolling direction, the double rolled β-PVDF exhibited notably enhanced dielectric and ferroelectric properties. Furthermore, due to the higher breakdown field and lower coercive electric field in comparison with the original β-PVDF films, the rolled β-PVDF films can be efficiently poled to obtain excellent piezoelectric properties. A maximum piezoelectric coefficient d33 of 29pC/N was obtained in the rolled β-PVDF films with a rolling temperature of around 50 °C.