Molecular Dynamics Analysis of Contact Line Depinning on Bubble Growth on the Wall Surface with Nano-Scaled Roughness.

The roughness on wall surfaces significantly affects the behavior of bubble nucleation and its growth during boiling. In this study, molecular dynamics simulations of bubble growth on a wall with periodic roughness were performed in order to examine the effect of nanoscale roughness on the contact line motion with bubble growth from a molecular-scale perspective. The contact line was pinned at the edge of the bumps, and its depinning behavior depended on the fluid density in the grooves. In this study, the depinning behavior is classified into three types based on the fluid density in the grooves. The first type was that the contact line was newly formed when the gas-liquid interface contacted the edge of neighboring bump, which occurred when the fluid density in the groove was same as that of the liquid phase. The second type was that the liquid molecules near the contact line detached from the top surface of the bump, which occurred when the fluid density in the groove was same as that of the gas phase. The third type was that the fluid density in the groove fluctuated between those of the liquid and gas phases, and the fluid in the groove was regarded as a part of the gas-liquid interface.