Thermal transport mechanism at a solid-liquid interface based on the heat flux detected at a subatomic spatial resolution.

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Heat flux is a fundamental quantity in thermal science and engineering and is essential for understanding thermal transport phenomena. In this study, the heat flux in a solid-liquid interfacial region is obtained in a three-dimensional (3D) space at a subatomic spatial resolution based on classical molecular dynamics, yielding a 3D structure of the heat flux between the solid and liquid layers in contact. The results using the Lennard-Jones potential reveal the directional qualities of the heat flux, which are significantly dependent on the subatomic stresses in the structures of condensed phase systems. The heat flux and stress at the subatomic scale are related to the macroscopic transport quantities, which can be obtained using distribution functions; the stress and energy flux properties at the subatomic scale are comprehensively investigated using a single-interaction-based stress and energy flux to determine the origin of the thermal transport mechanism at the solid-liquid interface. The findings reveal that the density of states due to the stress caused by a single interaction exhibits a bandlike behavior. The net energy transport comprises positive and negative energy transport inside and outside the band. In addition, this is related to the intrinsic transport property of the atoms and molecules at the solid-liquid interface at the subatomic scale. The difference between the energy transport rates when a solid atom in the vicinity of the interface is near to or far from the liquid phase is the origin of the energy transport mechanism at the solid-liquid interface. 3D analysis of the heat flux and stress is carried out by varying the interaction strengths between the liquid molecules and solid atoms at the solid-liquid interface. This reveals that the directional quality of transport quantities is high at strong interaction strengths, thus indicating enhanced thermal transport. Furthermore, the influence of the temperature gradient in the system suggests that the energy transport imbalance between inside and outside the stress band in a high-stress field at the subatomic scale induces the net thermal transport across the interface in the nonequilibrium state.