Aligned P(VDF-TrFE) Nanofibers for Enhanced Piezoelectric Directional Strain Sensing

Piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibers fabricated by electrospinning have drawn increasing levels of attention in the fields of flexible sensors and nanogenerators. However, the directional dependence of piezoelectricity of electrospun nanofibers remains elusive. In this study, the piezoelectric performances of individual nanofibers are characterized by piezoresponse force microscopy (PFM), while the effects of annealing on β-phase crystallinities are investigated by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The experimental results reveal that the as-spun P(VDF-TrFE) nanofibers form higher content of β-phase compared with spin-coated films, and the content of β-phase increases by annealing. The annealed P(VDF-TrFE) nanofiber exhibits distinct vertical polarization switching characteristics. The high piezoelectric output in the thickness direction and low piezoelectric output in the longitudinal direction of the nanofiber mats further confirm that the preferential dipole orientation of electrospun P(VDF-TrFE) nanofibers is normal to the surface of the substrate. Highly aligned P(VDF-TrFE) nanofibers show directional strain sensing ability due to the piezoelectric and mechanical anisotropy