Simulations of Heat Conduction at Thiolate-Capped Gold Surfaces: The Role of Chain Length and Solvent Penetration

We report on simulations of heat conduction through Au(111)/hexane interfaces in which the surface has been protected by a mixture of short- and long-chain alkanethiolate ligands. Reverse nonequilibrium molecular dynamics (RNEMD) was used to create a thermal flux between the metal and solvent, and thermal conductance was computed using the resulting thermal profiles near the interface. We find a nonmonotonic dependence of the interfacial thermal conductance on the fraction of long chains present at the interface and correlate this behavior to both solvent ordering and the rate of solvent escape from the thiolate layer immediately in contact with the metal surface. Our results suggest that a mixed vibrational transfer/convection model is necessary to explain the features of heat transfer at this interface. The alignment of the solvent chains with the ordered ligand allows rapid transfer of energy to the trapped solvent and is the dominant feature for ordered ligand layers. Diffusion of the vibrationally excited solvent into the bulk also plays a significant role when the ligands are less tightly packed.