Wetting behavior of low surface tension liquids on surface with re-entrant topological features

Abstract

Lophobic surfaces have been widely used in many emerging fields. In view of the diversity of working fluids in industrial production, controlling the wetting behavior of droplet with low surface tension has become the focus of many researches. Bionic studies have found that springtails could move freely on the water surface by means of its special-shaped microstructures with re-entrant angles on its skin surface. Based on the movement characteristic of springtails on the water surface, various forms of special-shaped surfaces have been developed for theoretical research, numerical simulation and experimental exploration. The local infiltration phenomenon of droplets on a special-shaped microstructure surface made the final suspension state of droplets unable to be characterized by the traditional Cassie equation. In this study, the silicon-based re-entrant microstructure surface was prepared by lithography, and a visualized system was set up. The wetting behavior of ethanol solution droplets with different concentrations on the re-entrant microstructure surface with different structure spacing was experimentally studied, and the wetting equation corresponding to the suspension state of the droplets on the special-shaped microstructure surface was theoretically derived. The results showed that the re-entrant microstructure surface could make the intrinsic lyophilic droplet become lyophobic. The decrease of structure spacing was beneficial to the formation of the Cassie state of droplet, but not conducive to the droplet rolling behavior. The larger the volume of droplet, the easier it was to roll on the structure surface. The droplet wicking phenomenon was a process from local breakthrough to overall spreading, so maintaining the structure integrity of surface was an important index to measure the surface lyophobic property.