A molecular dynamics study on heat conduction characteristics inside the alkanethiolate SAM and alkane liquid

In the present study, we performed molecular dynamics (MD) simulations of the self-assembled monolayer (SAM) and alkane solvent interface. In particular, 1-dodecanethiol (C12H25S) SAM chemisorbed on a gold substrate contacting with n-dodecane (C12H26) solvent was examined to compare the heat transfer mechanisms inside both the SAM and solvent phases from a microscopic viewpoint. The nonequilibrium MD (NEMD) simulation, in which a constant heat flux across the SAM interface was imposed, was performed. Here, we introduced the novel approach to clarify the molecular-scale mechanism on heat conduction in both SAM and alkane solvent. This approach enables us to decompose the macroscopic heat flux into the microscopic “building blocks”, i.e., the contribution of energy transfer associated with molecular motion and those of energy exchange by intermolecular (nonbonded) and intramolecular (covalent bond) interactions. Interestingly, we have obviously demonstrated that inside the SAM layer, almost all of the energy is transferred by the intramolecular interaction along the alkyl chain. On the other hand, inside the alkane liquid, the intramolecular and intermolecular interactions have similar contributions to the total heat flux in spite of the same molecular structure and alkyl chain length as the SAM molecules. This striking difference in heat conduction mechanism originates from the ordering structure of alkyl chains in the SAM layer.