Polyvinylidene fluoride‐natural graphite flexible composite films: Formation of graphite nanosheets, electroactive phase, analysis of electrical and thermal properties

Solution blending technique has been employed to synthesize polyvinylidene fluoride (PVDF)‐natural graphite composite films. The surface tension of the solvent has been observed to play an important role in the reduction of graphite particle size and their dispersion in the polymer matrix as N‐N‐dimethylacetamide (DMAc) employed PVDF‐x wt% natural graphite (x = 3, 5) films exhibit higher conductivity than that of N‐N‐dimethylformamide (DMF) employed films of same composition. The dispersion of probe sonicated graphite particles in PVDF matrix has been observed to be better when DMAc solvent is used in comparison to DMF employed composite as revealed by optical microscope images. The electrical percolation threshold in PVDF‐natural graphite composites is identified below 0.5 wt% natural graphite due to remarkable reduction in the particle size of graphite which improved the network formation between them. FESEM analysis confirms the formation of graphite nanosheets. The coexistence of non‐polar α and electroactive γ phases of PVDF in the composites is confirmed by FTIR, XRD, and DSC analyses. Maximum fraction of γ phase, as calculated from FTIR, is 88% in PVDF‐3 wt% natural graphite composite. Thermal annealing of PVDF‐3 wt% natural graphite at 120°C for 5 h results in enhanced electroactive γ phase in the nanocomposite. The onset degradation temperature of PVDF is increased by 4°C in PVDF‐5 wt% natural graphite suggesting enhanced thermal stability of the composite. Room temperature I–V characteristics of PVDF‐x wt% natural graphite (x = 5, 7) composite supports space charge limited conduction to be the dominant mechanism of charge transport.