Toru Kawaguchi

A molecular dynamics study on heat transfer characteristics at the interfaces of alkanethiolate self-assembled monolayer and organic solvent

In this paper, we present molecular dynamics (MD) simulations of interfaces composed of self-assembled monolayers (SAMs) and solvents in order to investigate the heat transfer characteristics at the interface. Two typical normal alkylthiolate SAMs with different chain lengths, i.e., 1-propanethiol C(3)H(7)SH and 1-dodecanethiol (C(12)H(25)SH) chemically adsorbed on Au(111) substrate surfaces, were used, and toluene was adopted as the organic solvent. In addition to the SAM systems, an interface composed of the bare solid substrate and solvent (without SAMs) was analyzed for comparison. Nonequilibrium MD simulations, in which a temperature gradient perpendicular to the interface was imposed, were performed and the difference in thermal boundary resistance in the interface systems was discussed. We observed that the SAM interfaces have smaller thermal resistance when compared with that of the bare solid interface. In order to understand the mechanisms of the small resistance at the SAM-solvent interfaces, the vibrational character of molecules in each phase, which contacted each other at the interface was analyzed and a detailed adsorbed structure of solvent molecule in the interface region was extracted. As a result, a clear difference in these characters was found between the SAM interfaces and bare solid interface.

A Molecular Dynamics Study on Heat Transfer Characteristics Over the Interface of Self-Assembled Monolayer and Water Solvent

We performed molecular dynamics simulations of the interface which is comprised of self-assembled monolayer (SAM) and water solvent to investigate heat transfer characteristics. In particular, local thermal boundary conductance (TBC), which is an inverse of so-called Kapitza resistance, at the SAM–solvent interface was evaluated by using the nonequilibrium MD (NEMD) technique in which the one-dimensional thermal energy flux was imposed across the interface. By using two kinds of SAM terminal with hydrophobic and hydrophilic properties, the local TBCs of these interfaces with water solvent were evaluated, and the result showed a critical difference due to an affinity between SAM and solvent. In order to elucidate the reason for this difference, microscopic components contributing to thermal energy flux across the interface were evaluated in detail, i.e., the total thermal energy flux is decomposed into the contribution of molecular transport and that of energy exchange by molecular interactions.Copyright