Tunneling and percolation transport regimes in segregated composites

TL;DR

This paper investigates how segregation in conductor-insulator composites enhances electrical conductivity by reducing interparticle distances and lowering percolation thresholds, using Monte Carlo simulations and effective-medium theory.

Contribution

It introduces a comprehensive model for tunneling and percolation transport in segregated composites, validated by simulations and theoretical analysis.

Findings

Segregation significantly increases conductivity by decreasing interparticle distances.

Effective-medium theory accurately predicts conductivity in segregated systems.

Percolation thresholds are lowered in lattice-segregated composites, enhancing conduction.

Abstract

We consider the problem of electron transport in segregated conductor-insulator composites in which the conducting particles are connected to all others via tunneling conductances, thus forming a global tunnelingconnected resistor network. Segregation is induced by the presence of large insulating particles, which forbid the much smaller conducting fillers from occupying uniformly the three-dimensional volume of the composite. By considering both colloidal-like and granular-like dispersions of the conducting phase, modeled respectively by dispersions in the continuum and in the lattice, we evaluate by Monte Carlo simulations the effect of segregation on the composite conductivity {\sigma}, and show that an effective-medium theory applied to the tunneling network reproduces accurately the Monte Carlo results. The theory clarifies that the main effect of segregation in the continuum is that of reducing the mean interparticle distances, leading to a strong enhancement of the conductivity. In the lattice-segregation case the conductivity enhancement is instead given by the lowering of the percolation thresholds for first and beyond-first nearest neighbors. Our results generalize to segregated composites the tunneling-based description of both the percolation and hopping regimes introduced previously for homogeneous disordered systems.