Role of surface roughness on thermal conductance at liquid–solid interfaces

The fractal Cantor structure is introduced to characterize the surface topography of solid wall. By this fractal characterization, a molecular dynamics simulation of heat conduction in rough nanochannels is conducted to investigate how surface topography affects the thermal conductance at liquid–solid interfaces. The role of surface roughness on temperature profiles, liquid atom trajectories, interfacial interaction energy and interfacial conductance are all examined and analyzed. The results indicate that, the temperature jump at liquid–solid interfaces is observed irrespective of surface condition, and the existence of surface roughness reduces the interfacial temperature jump. When compared with smooth surface, the presence of surface roughness diminishes the motion capability of liquid atoms in the wall-neighboring region and these atoms could maintain contact with the solid surface for a long time, which intensifies the energy transfer between the liquids and solid surface and hence contribute to large thermal conductance at a liquid–solid interface. Interestingly, it is found that the thermal conductance at a rough liquid–solid interface is affected by more than just statistical roughness height, but also fractal dimension (topographical irregularity). In addition, increases in liquid–solid interaction strength, roughness height and fractal dimension are all beneficial to enhance thermal conduction at liquid–solid interfaces. In particular, a longer trapping time of liquid atoms inside the valley of the fractal surfaces is observed for a larger fractal dimension.