Effect of annealing treatment on PVDF nanofibers for mechanical energy harvesting applications

Piezoelectric nanofibrous films with superior flexibility have attracted the emerging applications including sensors and actuators, piezoelectric nanogenerators (PNG) and energy storage devices. Herein, polyvinylidene fluoride (PVDF) piezoelectric nanofibrous film have been made by the electrospinning technique and been exposed to annealing as a post processing treatment at 40, 70, 100 and 130 degrees C for 4 h in air-flow oven. Four kinds of samples annealed at various temperatures have been pointed out as PVDF40, PVDF70, PVDF100 and PVDF130, respectively. The crystalline phases and thermal responses of the annealed film have been examined with XRD, FTIR and DSC. Also, mechanical and electroactive investigations exhibited that annealing treatment has effectively enhanced the dielectric constant, piezoelectric coefficient and the polar beta-phase. Moreover, the annealed PVDF film acts as an effective layer of the PNG with enhanced crystalline structure and polar beta-phase fraction. When the film is annealed at 100 degrees C, the voltage output of the PNG can attain maximum microstrain of 1000 mu epsilon. The developed PVDF100 nanofibrous film-based PNG can generate output voltage of 0.516 V and 0.505 V with a tensile and compressive microstrain measured using the microstrain indicator of 1000 mu epsilon. It shows better results compared to PVDF40 of 0.221 V. The enhanced voltage output of the PNG is recognised to be the collaborative involvement of the electrospinning and annealing treatment which could improve the piezoelectric response of the annealed film. This work presents that the annealed PVDF nanofibrous film based highly compliant PNG could be a promising candidate for flexible self-powered electronic applications.