Enhanced thermal conductivity in percolating nanocomposites: a molecular dynamics investigation

TL;DR

This study uses molecular dynamics to reveal a significant, unexpected enhancement in thermal conductivity in silica-gallium nitride nanocomposites due to phonon tunneling and particle orientation, surpassing predictions of traditional models.

Contribution

It demonstrates a stronger-than-expected percolation effect on thermal conductivity, highlighting the role of phonon tunneling and particle orientation in nanocomposites.

Findings

Thermal conductivity increases notably above 5% crystalline volume fraction.

Effective volume fraction for percolation is twice the actual, indicating enhanced tunneling.

Orientation of particles significantly influences thermal transport.

Abstract

In this work we present a molecular dynamics investigation of thermal transport in a silica-gallium nitride nanocomposite. A surprising enhancement of the thermal conductivity for crystalline volume fractions larger than 5% is found, which cannot be predicted by an effective medium approach, not even including percolation effects, the model systematically leading to an underestimation of the effective thermal conductivity. The behavior can instead be reproduced if an effective volume fraction twice larger than the real one is assumed, which translates in a percolation effect surprisingly stronger than the usual one. Such scenario can be understood in terms of a phonon tunneling between inclusions, enhanced by the iso-orientation of all particles. Indeed, if a misorientation is introduced, the thermal conductivity strongly decreases. We also show that a percolating nanocomposite clearly stand in a different position than other nanocomopsites, where thermal transport is domimnated by the interface scattering, and where parameters such as the interface density play a major role, differently from our case.