Influence of small amount of wetting impurity on the slip of liquid flowover non-wetting surface

The nanofluidic systems has great promise applications in many areas because of high efficiency and economic performance. During to the very large rate of surface and volume, the interface slip effect will significantly influence the flow properties in nanofluidic systems. The non-equilibrium molecular dynamics simulation was used to investigate the slip properties as liquid flows past non-wetting solid wall which contains small amount of wetting impurity. The underlying mechanism was also discussed based on the molecular kinetic theory. The simulation results indicate that the wetting impurity (uniformly or concentrated distributed) show insignificant influence on density profile of liquid but significantly alters the solid-like structure and slip property of liquid. As the percent of wetting impurity increasing, the solid-like phenomenon of liquid near walls becomes more significant and the contact density increases linearly. At the same time, the average velocity of liquid decreasing and the slip length decreases fast in a linearly way. The uniformly distributed wetting impurity reduces the magnitude of slip more significantly than concentrated distributed at the same percent of wetting impurity. For example, as the percent of wetting impurity is 28%, the slip length decreases 50% (concentrated distributed) and 56% (uniformly distributed) relative to the homogeneous non-wetting wall. The analysis based on the molecular kinetic theory indicates that the existence of wetting impurity enlarges the energy barrier as liquid atoms hopping from one sites to another in the first liquid layer. Thus, the probability of liquid atoms hoping along the flow direction was decreased, i.e. smaller the slip length. In the case of uniformly distributed wetting impurity, the smaller slip arbitrated to the decreasing incommensurability between fluid and wall.