Formation of piezoelectric β-phase crystallites in poly(vinylidene fluoride)-graphene oxide nanocomposites under uniaxial tensions

A combination of chemical addition and mechanical deformation is employed to develop a nearly pure beta crystalline phase in poly(vinylidene fluoride) (PVDF). The mechanical strains for the formation of pure beta phase in PVDF-graphene oxide (PVDF-GO) nanocomposites are found to be only half of that for PVDF deformed at the same temperature. Based on the creep experiments, piezoelectric force microscopy and mechanical anelastic relaxation, it is shown that the attachments of PVDF molecule chains to the GO sheets caused by the interaction between the -CF2 or -CH2 groups of PVDF and the functional groups of GOs could facilitate the formation of piezoelectric beta-phase crystallites in the stretched nanocomposites. A model is proposed to elucidate the easy formation of the piezoelectric beta phase in the PVDF-GO nanocomposites under uniaxial tensions.