High performance piezoelectric polymer film with aligned electroactive phase nanofibrils achieved by melt stretching of slightly crosslinked poly(vinylidene fluoride) for sensor applications

Flexible, transparent and lightweight polymer piezoelectric films are promising for emerging sensor applications, including wearable electronics and human–machine interfaces. However, it remains a great challenge for large-scale fabrication of high-quality polymer piezoelectric films by a cost-effective melt processing approach, mainly due to the difficulty of acquiring well-defined electroactive phases. Herein, a readily implementable and scalable strategy is reported to achieve poly(vinylidene fluoride) (PVDF) film with ultrahigh content of electroactive β-phase (∼96%) via melt stretching of slightly crosslinked PVDF. Upon controlled temperature and stretch ratio, the β-phase adopts an oriented nanofibril (diameter, 21.6 nm) morphology, while nanofibrils are further densely and parallelly aligned to fill the film space. The hierarchical nanoscale phase morphology endows the slightly crosslinked film with high optical transmittance (∼90%), good flexibility and also superior mechanical properties. Moreover, flexible piezoelectric device constructed on the film is demonstrated to have excellent electrical output with sensitive and repeatable responses in sensing dynamic pressure (0–250 kPa), temperature variation (3.3 mV oC-1), human motions and subtle physiological activities. This study therefore paves the way towards scalable manufacturing of high-performance piezoelectric polymer film through simple melt stretching.