ZnO-poly(acrylonitrile) composite films with improved piezoelectric properties for energy harvesting and sensing applications

Piezoelectric nanogenerators are one of the possible solutions for generating power in milliwatts for various mobility applications. They can also be utilized as tactile sensors. Since poly(acrylonitrile) (PAN) has a greater dipole moment (3.5 D) than poly (vinylidene fluoride) (PVDF), it has a strong potential for use as piezoelectric nanogenerators and pressure sensors. However, due to strong dipole-dipole repulsion, the nitrile groups are difficult to align in a zig-zag configuration resulting in reduced ability of the system to convert mechanical energy into electrical energy. To address this issue, we have incorporated ZnO nanoparticles (ZnP) and ZnO nanowires (ZnW) in PAN films. Due to the strong interaction of ZnO nanostructures with PAN, the dipole-dipole repulsion reduces resulting in increased zigzag conformation of PAN. Compared to ZnP, ZnW was found to show better alignment of PAN nitrile groups and faster relaxation of dipoles after removal of stress. Without any external poling, PAN, ZnP-PAN, and ZnW-PAN films based piezoelectric nanogenerators could generate 27.6, 79.3 and 86.3 mW/m2 of power, respectively. The incorporation of 5 wt% ZnP and ZnW also significantly improved the pressure sensitivities of the devices to 0.9 fFPa−1 and 1.1 fFPa−1, respectively, as compared to 0.1 fFPa−1 for pristine PAN film.