Enhanced Piezoelectric Performance of Various Electrospun PVDF Nanofibers and Related Self-Powered Device Applications.

The piezoelectric polymer poly(vinylidene fluoride) (PVDF) has been widely employed for energy harvesting or sensors. Its piezoelectricity originates from the unique crystal structure and the oriented electric dipoles. Generally, electrospinning (ES) is able to improve the crystallinity and piezoelectricity of PVDF. In this investigation, three types of ES, including far-field ES with random (R-PVDF-FFES) or aligned distribution (A-PVDF-FFES) and near-field ES (PVDF-NFES), are applied to fabricate a one-step polarized PVDF membrane. To compare the piezoelectricity of separated PVDF-NFES fibers, the array of PVDF-NFES fibers is encapsulated in polylactic acid (PLA). The result shows that the piezoelectricity of PVDF is dramatically enhanced by NFES and FFES. In d31 mode, the current density of PVDF-NFES-PLA is 75.63 pA cm-2 with a 2 Hz shear force, which is four times larger than A-PVDF-FFES (17.62 pA cm-2) or seven times larger than R-PVDF-FFES (10.63 pA cm-2). Due to its outstanding property, the PVDF-NFES-PLA membrane is designed to be applied as a self-powered device. The unimorph cantilevers are prepared to harvest the vibration energy and their output power density reaches 95.3 μW m-2 at a resonance frequency of 31 Hz. Meanwhile, the flexible bending sensor and pressure sensor are fabricated with a PVDF-NFES-PLA membrane, which shows the stable response for pressure with sensitivity values of 864.68 and 22.6 mV kPa-1, respectively.