Investigations of structure development, electrical and thermal properties of polyvinylidene fluoride-expanded graphite nanocomposites

From natural graphite, expanded graphite (ExGr) has been synthesized using perchloric acid. Polyvinylidene fluoride (PVDF)-ExGr nanocomposites have been synthesized through non-solvent precipitation method followed by melt crystallization at 200 degrees C and quenching in water at room temperature. The electrical percolation threshold has been found to be above 4 wt% ExGr in PVDF. With the addition of 0.5 wt% sonicated ExGr in PVDF-7 wt% graphite, the electrical conductivity is enhanced to two orders when compared to that of PVDF-7 wt% graphite. Thermogravimetric analysis proves very good dispersion of graphite nanosheets, as there exists at least 20 degrees C enhancement in the onset temperature of thermal degradation with the addition of 3 wt% ExGr in PVDF. Structure development in PVDF due to the incorporation of ExGr particles has been understood through lattice mismatch theory. The impedance decreases with increase in the concentration of ExGr in PVDF at room temperature due to the formation of conducting channels. In another set of experiment, annealing of solution-casted films at 120 degrees C for 5 h results in the formation of electroactive gamma-phase, as confirmed through Fourier transform infrared and X-ray diffraction (XRD) analyses of representative samples. The composites are characterized by XRD, scanning electron microscopy and transmission electron microscopy.