Development of Flexible Piezoelectric Nanogenerators From Electrospun Nanofabrics of Poly(Vinylidene Fluoride)/Nanosheets Composites

Abstract

Poly(vinylidene fluoride) (PVDF) is a versatile polymer due to its dielectric, piezoelectric and ferroelectric properties. However, a range of processing routes and/or additives is often necessary to enhance such properties. In this study, PVDF nanocomposite based electrospun nanofabrics were synthesized for piezoelectric energy-harvesting applications. Functional nanofillers such as organically modified Ni-Co layered double hydroxide (OLDH), talc nanosheets, and carboxyl functionalized graphene nanosheets (FGNS) were used to tune the electroactive β- phase of PVDF. Morphology, crystallinity, polymorphism, dielectric, and piezoelectric properties of these nanofabrics were studied in detail. The presence of these nanofillers in PVDF nanofabrics led to the enhancement of the polar β-phase in PVDF, which was corroborated from the results of Fourier transform infrared spectroscopy and X-ray diffraction. A nanogenerator, that was custom made from the OLDH/PVDF nanofabrics exhibited a maximum output voltage of 6.9 V and power density of 0.92 μW/cm2 under human finger tapping mode. The synergistic effect of OLDH and electrospinning contributed to the enhancement of the β-phase content, thereby the piezoelectric response of the OLDH/PVDF composite nanofabrics. The electromechanical response of talc nanosheets/PVDF composite nanofibers was studied using piezoresponse force microscopy and accordingly exhibited well-defined ferroelectric characteristics with an enhanced piezoelectric coefficient (d33) of 43.3 pm/V compared to 10 pm/V measured for the pristine PVDF nanofibers. It was observed that the piezoelectric coefficient values strongly depended on the morphology and electroactive phase fraction of the ensuing composite nanofiber. Also, these talc nanosheets/PVDF composite nanofabrics recorded a maximum piezoelectric response of 9.1 V. Finally, the developed talc nanosheets/FGNS/PVDF hybrid composite nanofabrics resulted in an enhanced piezoelectric response of 12.9 V and 61 pm/V, respectively. The advantage of a high aspect ratio, surface charges, and electrically conductive network offered by nanofillers alongside the electrospinning augmented the composite nanofibers’ piezoelectric response. Improved flexibility, mechanical robustness, and enhanced piezoelectric responsiveness of these PVDF based composite nanofabrics could possibly pave the way to their use in flexible energy-harvesting devices.