Phonon Transport and Thermal Conductivity Percolation in Random Nanoparticle Composites

In this paper, we investigated the effective thermal conductivity of three dimen-sional nanocomposites composed of randomly distributed binary nanoparticles with large differ-ences (contrast ratio) in their intrinsic (bulk) ther-mal conductivity. When random composites are made from particles with very different thermal conductivity (large contrast ratio), a continuous phase of high thermal conductivity constituent is formed when its volumetric concentration reaches beyond the percolation threshold. Such a contin-uous phase of material can provide a potentially low resistance pathway for thermal transport in random composites. The percolation theory pre-dicts the thermal conductivity of the random com-posites to increase according to a scaling law with increasing concentration of the high thermal con-ductivity constituent after percolation. However, when the characteristic size of the particles in the nanocomposites is comparable to or smaller than the phonon mean free path, the phonon scattering at interfaces between two materials can introduce significant thermal resistance in the highly con-ductive phonon pathway. Such interfacial thermal resistance can reduce the thermal conductivity of the nanoparticle composites. The thermal con-ductivity of the random nanoparticle composites thus deviates significantly from the predictions of the percolation theory. In this study, the Monte Carlo simulation was employed to generate ran-dom distribution of nanoparticles and to simulate the phonon transport in random nanoparticle com-posites. The effects of particle size, thermal con-