Homogeneous poly(vinylidenefluoride)-graphene films with secondary percolation behaviors towards negative permittivity properties

With tunable negative permittivity, flexible and collapsible films composed of polyvinylpyrrolidone modified graphene and poly(vinylidene fluoride) were fabricated by solution casting method. Interestingly, a secondary percolation behavior was observed from σac, and two percolation thresholds ranged from 3.75 to 6.25 wt% and 12.5 to 18.75 wt%, respectively. Meanwhile, the results indicated that the obtained composite films achieved negative permittivity at a lower GR content (3.75 wt%), which was ascribed to better dispersion of the modified GR in the matrix. The negative dielectric curves could be well in accordance with Lorentz model and Drude model, respectively. It was also first discovered that different types of negative dielectric behavior corresponded well to the two percolation phenomena of σac, which was ascribed to the different microstructures.