Dynamics of electric charge transport and determination of the percolation insulator-to-metal transition in polyvinyl-pyrrolidone / nano-graphene platelet composites

TL;DR

This study investigates how nano-graphene platelet concentration affects charge transport and the insulator-to-metal transition in PVP composites using dielectric spectroscopy, revealing a percolation threshold influenced by quantum effects.

Contribution

It provides new insights into the percolation behavior and charge dynamics in PVP/nano-graphene composites, highlighting the quantum penetration effects at the threshold.

Findings

Identification of the insulator-to-conductor transition point.

Observation of different dielectric dynamics below and above the threshold.

Confirmation of quantum penetration influencing percolation.

Abstract

Polyvinyl-pyrrolidone (PVP) loaded with different fractions of dispersed nano-graphene platelets (NGP) were studied by Broadband Dielectric Spectroscopy in the frequency range from 1 mHz to 1 MHz. Complex permittivity and dynamic ac conductivity as a function of frequency, temperature and composition were explored. The concentration-dependent insulator-to-conductor transition was traced through dependence of the dc conductivity and the onset of the dispersive ac ac conductivity. The temperature evolution of the dielectric spectra, below and above the fractional threshold exhibits different dynamics and signs the critical percolation threshold. Percolation is dictated by quantum penetration of the effective potential barrier set by the polymer matrix operating in parallel with conduction along physical contact of NGP, in accordance with predictions for systems consisting of a semi-conducting matrix and dispersed conducting inclusions.