Melt-stretched poly(vinylidene fluoride)/zinc oxide nanocomposite films with enhanced piezoelectricity by stress concentrations in piezoelectric domains for wearable electronics

Till date, fabrication of polymeric-inorganic piezoelectric nanocomposites with enhanced piezoelectricity is considered a potential solution for future high-performance flexible sensing devices. Herein, we report the preparation of poly(vinylidene fluoride)/zinc oxide (PVDF/ZnO) piezoelectric nanocomposite films via a combined approach of adding nanofillers, irradiation crosslinking and melt stretching. The melt-stretched film contains closely aligned β-phase nanofibrils with a high content (>90 % of the crystalline phase) serving as piezoelectric domains. Meanwhile, the incorporation of ZnO nanoparticles creates stress concentrations, promoting the piezoelectric response of β-nanofibrils and also the stress-induced polarization under loading. As a result, the film displays not only a superior mechanical strength (>100 MPa), but also largely enhanced piezoelectric output performance after poling, including wide response range, high sensibility to weak force and excellent working durability (>10,000 cycles). The optimal film with ZnO content of 5 wt% has a pressure sensitivity of ∼ 1.7 V/kPa under 0–1 kPa, almost twice that (∼0.8 V/kPa) of the pure PVDF without nanofillers. With the outstanding piezoelectric properties, potential applications of film as a flexible wearable sensor in monitoring human motions and subtle physiological signals are demonstrated. The results provide a new melt processing strategy that is easily scalable for developing high-performance PVDF-based piezoelectric nanocomposite films towards wearable electronics.