Electrical and optical percolation behavior of carbon nanotube-doped graphene reinforced polyvinylpyrrolidone/polymethyl methacrylate nanocomposite films

Abstract

In this study, multifunctional poly (vinylpyrrolidone)/poly (methyl methacrylate)/carbon nanotube-doped graphene (PVP/PMMA/CNTG) nanocomposite films were fabricated, and their electrical conductivity and optical transmittance were quantitatively analyzed within the framework of percolation theory. The pure PVP/PMMA blend exhibited an insulating behavior a very low electrical conductivity of 2.7 × 10^-7 S m^-1. Upon the incorporation of CNTG fillers, a dramatic enhancement in electrical conductivity was observed, reaching 2.46 × 10² S m^-1 at 3.00 vol% loading, corresponding to an increase of approximately nine orders of magnitude. Electrical percolation analysis revealed a low percolation threshold of ${\varphi }_{\sigma }$ = 0.30 vol%, which is attributed to the synergistic interaction between one-dimensional carbon nanotubes and two-dimensional graphene sheets forming an efficient three-dimensional conductive network. The critical exponent was determined to be $t_{\sigma }$ = 2.62, indicating a non-ideal, tunneling assisted three-dimensional percolation mechanism. Optical characterization performed at a fixed wavelength of 600 nm demonstrated a progressive decrease in optical transmittance with increasing CNTG content, due to enhanced photon scattering and absorption arising from refractive index mismatch and increased structural heterogeneity. In contrast to the electrical behavior, optical percolation occurred at a higher filler content, with an optical percolation threshold of ${\varphi }_{op}$ = 1.20 vol% and a critical optical exponent $t_{op}$ = 0.41, which is close to the theoretical site percolation value. A strong inverse correlation between electrical conductivity and optical transmittance was observed, highlighting the inherent trade-off between electrical performance and optical transparency.