Roughness Effects on Continuous and Discrete Flows in Superhydrophobic Microchannels

The dynamic behaviors of continuous and discrete flows in superhydrophobic microchannels are investigated with a lattice Boltzmann model.Typical characters of the superhydrophobic phenomenon are well observed from our simulations,including air trapped in the surface microstructures,high contact angles,low contact angle hysteresis,and reduced friction to fluid motions.Increasing the roughness of a hydrophobic surface can produce a large flow rate through the channel due to the trapped air,implying less friction or large apparent slip.The apparent slip length appears to be independent to the channel width and could be considered as a surface property.For a moving droplet,its behavior is affected by the surface roughness from two aspects:the contact angle difference between its two ends and the surface-liquid interfacial friction.As a consequence,the resulting droplet velocity changes with the surface roughness as firstly decreasing and then increasing.Simulation results are also compared with experimental observations and better agreement has been obtained than that from other numerical method.The information from this study could be valuable for microfluidic systems.