A molecular dynamics study on the thermal energy transfer and momentum transfer at the solid-liquid interfaces between gold and sheared liquid alkanes

Solid-liquid (S-L) interfaces of linear alkane liquids contacting two parallel solid walls of gold with three types of face-centered cubic (FCC) of (100), (110) and (111) crystal planes were examined using nonequilibrium molecular dynamics simulations (NEMD). The liquid alkanes were sheared by the two parallel solid walls sliding at a constant speed and in opposite directions, which generates viscous heating in the liquid. The effect of the molecular length of the linear alkane liquids, methane, butane, octane, and tetracosane, was investigated in terms of the thermal energy transfer and momentum transfer at the S-L interfaces. The gap distance between the surface layer of the solid atoms and the adsorption layer of the liquid molecules was measured as a key feature of the interface. The slip length, which was defined as the extrapolated velocity of liquid into the solid walls where the tangential velocity vanishes, was measured and the mechanism that determines its magnitude was examined. The gap distance and the slip length were correlated with the molecular length of the liquid alkanes. The thermal boundary resistance at the S-L interfaces was measured and it was also correlated with the gap distance and molecular length of liquid alkanes. It was found that the differences in the surface structure of the solid walls between the three types of crystal planes affect the slip length at the S-L interfaces. The present results suggest that the factors affecting the thermal energy transfer and momentum transfer at the S-L interfaces were the gap distance, which differs significantly depending on the molecular length of liquid, and the surface structure of the solid walls.