Molecular-Scale Mechanism of Thermal Resistance at the Solid-Liquid Interfaces: Influence of Interaction Parameters Between Solid and Liquid Molecules

The solid-liquid interfacial thermal resistance is getting more and more important as various solid-liquid systems are utilized in nanoscale, such as micro electro-mechanical systems/nano electro-mechanical systems (MEMS/NEMS) with liquids and nanoparticle suspension in liquids. The present paper deals with the transport of thermal energy through the solid-liquid interfaces, and the goal is to find a molecular-scale mechanism that determines the macroscopic characteristics of the transport phenomena. Nonequilibrium molecular dynamics simulations have been performed for systems of a liquid film confined between atomistic solid walls. The two solid walls have different temperatures to generate a steady thermal energy flux in the system, which is the element of macroscopic heat conduction flux. Three kinds of liquid molecules and three kinds of solid walls are examined, and the thermal energy flux is measured at the control surfaces in the liquid film and at the solid-liquid interfaces. The concept of boundary thermal resistance is extended, and it is defined for each degree of freedom of translational motion of the molecules. It is found that the interaction strength between solid and liquid molecules uniformly affects all boundary thermal resistances defined for each degree of freedom; the weaker interaction increases all the resistances at the same rate and vice versa. The boundary thermal resistances also increase when the solid and liquid molecules are incommensurate, but the incommensurability has a greater influence on the boundary thermal resistances corresponding to the molecular motion parallel to the interface than that for the normal component. From these findings it is confirmed that the thermal resistance for the components parallel to the interface is associated with the molecular-scale corrugation of the surface of the solid wall, and that the thermal resistance for the component normal to the interface is governed by the number density of the solid molecules that are in contact with the liquid.