Connectivity percolation in suspensions of hard platelets

TL;DR

This study investigates how the percolation threshold in suspensions of hard platelets depends on aspect ratio, revealing a non-monotonic behavior influenced by phase transitions, which challenges common assumptions for designing composite materials.

Contribution

It demonstrates that the percolation threshold for hard platelets does not follow the inverse aspect ratio rule and is affected by isotropic-nematic transitions, providing new insights into anisotropic particle networks.

Findings

Percolation threshold is non-monotonic in aspect ratio for platelets.

Isotropic-nematic transition influences percolation behavior.

Common strategies for low-concentration fillers may fail with plate-like particles.

Abstract

We present a study on connectivity percolation in suspensions of hard platelets by means of Monte Carlo simulation. We interpret our results using a contact-volume argument based on an effective single--particle cell model. It is commonly assumed that the percolation threshold of anisotropic objects scales as their inverse aspect ratio. While this rule has been shown to hold for rod-like particles, we find that for hard plate-like particles the percolation threshold is non-monotonic in the aspect ratio. It exhibits a shallow minimum at intermediate aspect ratios and then saturates to a constant value. This effect is caused by the isotropic-nematic transition pre-empting the percolation transition. Hence the common strategy to use highly anisotropic, conductive particles as fillers in composite materials in order to produce conduction at low filler concentration is expected to fail for plate-like fillers such as graphene and graphite nanoplatelets.