Theoretical Study On Didrected Wetting Behaviors Of Liquid On Microstructure Surface

It's reported that desert beetles are able to collect water from surroundings by their back,the spider as well as nepenthes alata can transport liquid directionally and droplets are free to roll on the lotus leaf.These interesting phenomena existing in nature have been broadening our understanding in design of functional materials for waterproof and anti-corrosion.The studies indicate that these phenomena are caused by the special micro/nano structure on its surface.Thus,it is significant to study the wetting behavior of liquid on the microstructures for understanding deeply of natural phenomena and facilitating industrial productions.In this work,we studied wetting behaviors of liquids on microstructures by Lattice Boltzmann Method(LBM)and main results are given as follows:(1)Firstly,theoretical calculations and two-dimentional LB simulations were conducted to investigate the interface effect of both chemical wetting gradient and anisotropic geometry pattern within microchannel on liquid directional flow.The results indicate that the traditional method to estimate interface barrier by calculating the difference of Laplace pressure at two equilibrium states is not quite appropriate.Actually,there are other factors existing,such as contact angle hysteresis and interfacial tensions.Finally,a general principal were proposed to regulate directional flow of microfludics by using anistropy of chemical gradient and geometry pattern.The principle has some guiding significance in predicting the direction of fluid and design of biomimetic materials for directional flow.(2)Secondly,we simulated the round interface effect by LBM.It is found that the interfacial effect of the round edge is much smaller than the straight one which has same apparent edge angle.(3)Lastly,we investigated the impact of drop on substrate which is composed of incline pillars.As is shown,the larger the pillars' incline angle is,the easier for the drop to rebound,and the middle incline angel is best for directional bounce.We conclude the difference of edge effect at two sides of pillar's top plays a key role in the impact results.The heterogeneous surface of pillar can lead to anisotropic receding of entrapped liquid and let drop rebound directionally.Based on foregoing principle,we optimized the substrate by mixing pillars of different incline angle,in which the less steep pillar only takes a tiny part.The results show that combination of different spaces of vertical pillars is optimal for achieving directional drop rebound.