Piezoelectric Response in Electrospun Poly(vinylidene fluoride) Fibers Containing Fluoro-Doped Graphene Derivatives

Herein, graphene oxide (GO) was suitably functionalized to obtain carboxylated and fluorinated GO (GOCOOH and GOF) derivatives, respectively, via the Hunsdiecker reaction. Electrospun mats of poly(vinylidene fluoride) (PVDF)/GO, PVDF/GOCOOH, and PVDF/GOF fibers were then prepared by electrospinning from well-dispersed GO derivatives. The piezoelectric coefficient (d(33)), as measured using piezoelectric force measurement (PFM), enhanced by more than 2 folds with respect to the control PVDF spun mat. The piezoelectric coefficient though enhanced upon the addition of GO and GOCOOH, however, enhanced significantly in the case of GOF. For instance, a drastic increase in piezoelectric response from 30 pm V-1(electrospun neat PVDF) to 63 pm V-1 (for electrospun PVDF/GOF) was observed as revealed from PFM results. The phase transformation in these fibers was systematically investigated by various techniques such as Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (XRD), Raman spectroscopy, and PFM. FTIR and XRD results revealed that the electrospun fiber mats showed predominantly beta-PVDF. Interestingly, the highest beta content was obtained in the presence of GOF. The drastic enhancement in beta phase is due to the presence of highly electronegative fluorine. The addition of GOCOOH and GOF in PVDF not only increases the polar beta phase but also changes the piezoelectric response significantly. More interestingly, PVDF/GOF films exhibited higher energy density and dielectric permittivity when compared with the control PVDF samples. These findings will help guide the researchers working in this field from both theoretical understanding and practical view point for energy storing device and charge storage electronics.