Poly (vinylidene fluoride)/graphene oxide nanocomposites for piezoelectric applications: Processing, structure, dielectric and ferroelectric properties

Graphene oxide (GO) based poly (vinylidene fluoride) (PVDF) nanocomposites were prepared using high-shear solution mixing followed by compression moulding, with the aim to enhance the ferroelectric and piezoelectric properties of PVDF/GO nanocomposites. Prior to the high-shear mixing, ultrasonication alone and ultrasonication followed by centrifugation of GO were used to exfoliate GO. Optical microscopic observations indicated an increase in the GO ‘agglomerate’ size in the PVDF matrix, the increase being ∼1.5 to ∼ 2.9μm as the GO concentration was increased from 0.05 to 0.50 wt%. However, the PVDF/GO composite of 0.18 wt% GO showed an ‘agglomerate’ size of ∼ 1.6μm, which indicates the influence of ‘centrifugation’ along with ultrasonication in obtaining a finer dispersion of GO. FEG-SEM morphological investigations revealed GO stack thicknesses of ∼0.6 and ∼ 0.09μm at 0.15 and 0.18 wt% GO in the PVDF/GO nanocomposite, whereas the pure GO film showed an average stack thickness of ∼ 1.35μm. FTIR spectroscopic analysis showed the variation of -CF2 peak shift as a function of GO concentration, which indicates a maximum peak shift in the case of the PVDF/GO composite of 0.15 wt% GO, suggesting the highest extent of interfacial interaction. Moreover, FTIR analysis established that the PVDF/GO nanocomposite of 0.15 wt% GO showed a maximum polar phase fraction of ∼61%. The PVDF/GO nanocomposite of 0.15 wt% GO exhibited the highest dielectric constant of ∼119 at 0.1 Hz, which showed a remnant polarization Pr value of 0.0014 μC/cm2. The PVDF/GO nanocomposite of 0.15 wt% GO exhibited a d33 value of ∼36 pm/V, as estimated from piezoresponse force microscopy, which was significantly higher as compared to pure PVDF. Further, strain-sensing investigations revealed maximum peak-to-peak voltages of ∼3 and ∼4 V corresponding to PVDF/GO nanocomposites of 0.15 and 0.18 wt% GO, respectively.