Enhancement of physical, mechanical, and gas barrier properties in noncovalently functionalized graphene oxide/poly(vinylidene fluoride) composites

Sulfonated poly(ether-ether-ketone) functionalized graphene oxide (SPG)/poly(vinylidene fluoride) (PVDF) composites have been prepared by a solvent evaporation technique. The -SO3H group of SPG interact with the >CF2 dipole of PVDF to integrate graphene uniformly into a PVDF matrix. The cross-sectional field emission scanning electron microscopy micrograph shows folded-chain lamella of spherulitic PVDF crystallites spread outwards from the growth center. The spherulitic crystallites decrease with the incorporation of SPG into the PVDF matrix and the composite containing 3 wt.% SPG (SPG3) does not show spherulite, but fiber-like crystallites. Fourier transform infrared spectroscopy, wide angle X-ray scattering and differential scanning calorimetry (DSC) results suggest that piezoelectric β-polymorph formation begins with the incorporation of SPG into the PVDF matrix, and SPG3 shows the formation of the fully β-polymorph. DSC cooling curves show that SPG acts as an effective nucleating agent for the crystallization of PVDF. Study of the mechanical properties shows that there is a simultaneous enhancement of the stress and the strain at break indicating the enhanced toughness of the PVDF composites compared to pure PVDF. Young's modulus increases 160% and the oxygen permeability coefficient decreases by 91% in the SPG3 composite film compared to pure PVDF.