Exploration of Interfacial Thermal Conductance of Gold Nanoparticles Using Molecular Dynamics

In this dissertation I present work on the factors important to heat transport in gold nanostructures, particularly nanoparticles. I examine the effect of particle size, ligand layer rigidity, and surface gold vibrational freedom. The interfacial thermal conductance of various particle morphologies, as well as the thermal conductivity of nanoarrays, display trends of how heat transport is affected by particle size, shape, and volume fraction of a system. Direct simulations of interfacial thermal conductance of solvated gold nanoparticles were carried out using molecular dynamics.

Nanoparticles created in vitro contain a ligand layer at the surface of each particle that prevents aggregation and is a result of the method used in the synthesis of the particles. This moiety controls the movement of heat from a particle to the surrounding media. In particular, looking closely at how the rigidity of this ligand layer (and the length of the ligand) change thermal transport across the solvent-particle interface. This provides further insight into the factors that govern heat flow. Proposed mechanisms for heat transfer rely on two effects: the vibrational spectral overlap of the materials at the interface and the physical contact between the same materials.

Finding no direct relationship between particle size with the ligand layer and the thermal transport, a simpler system was examined: bare nanoparticles in a non-polar solvent. The particles consist of nanospheres, icosahedra, and cuboctahedra. The latter two structures display facets that are common in many nanostructures due to their stability. The interfacial thermal conductance (G) of the particles was examined as a function of particle radius and morphology. The coordination of gold atoms at the particle surface, which provides information about the vibrational spectrum, displayed a small correlation with G. This lends support to the proposed factors for heat transport that were discovered while investigating ligands.

The ideas from both previous chapters are combined to study Au_{144>/sub>PET60 particles, in both isolation, and in a nanoarray. These small particles (r ≈ 10 A) have highly undercoordinated gold atoms in the ligand layer. The thermal conductivity of the composite material is predicted using bulk properties and an estimation of boundary resistance. This prediction uses individual components of the composite systems, and is compared to results for simulated nanoarrays. In the predicted conductivity, the nanoarray thermal conductivity depends mostly on the geometric feature, vp, the particle volume fraction.}