Structure–Piezoelectric Property Relationships of Thin Films Composed of Electrospun Aligned Poly(vinylidene fluoride) Nanofibers

In the past two decades, many studies on piezoelectric nanofibers (NFs) prepared from poly(vinylidene fluoride) (PVDF) and its copolymers, including single NFs, randomly oriented nonwoven mats, and aligned NFs, have been reported. However, studies on the relationships between the PVDF NF diameter, the orientation of the β-phase crystals inside NFs, and the piezoelectric properties of the NFs are still limited. In this study, the effect of the fiber diameter on the internal molecular packing/orientation and piezoelectric properties of aligned PVDF NF thin films was investigated. Herein, piezoelectric thin films composed of densely packed, uniaxially aligned, PVDF NFs with diameters ranging from 228 to 1315 nm were prepared by means of electrospinning with a rotating collector and successive hot-pressing and poling. The effect of the diameters of PVDF NFs on their internal structures, as well as the piezoelectric properties of the thin films, was investigated. All prepared NFs mainly contained β-phase crystals with a similar total crystallinity. The orientation of the β-phase crystals inside the NFs increased with an increase in the fiber diameter, resulting in an improved transverse piezoelectric coefficient (d31) for the thin films. The output voltage of the prepared thin films reached a maximum of 2.7 V at 104 Hz.