Underwater Stability Of Trapped Air Layer And Wettability On Superhydrophobic Surface

It is known that the superhydrophobic surface can tap air in its rough grooves under water. The trapped air layer makes the underwater wettability of superhydrophobic surface possess lots of promising application, such as marine antifouling, anti-drag and so on. And because of the trapped air, the wetting with oil underwater on superhydrophobic surface becomes a complex liquid/liquid/air/solid multi-phase interface. For now, the study about stability of trapped air and the wettability with oil on superhydrophobic surface under water is not very much. In this paper, the influence of trapped air on underwater oil-wetting behavior of superhydrophobic surface has been investigated. Furthermore, we have explored the mechanization of oil-wetting behavior on superhydrophobic surface under water. In addition, the stability of trapped air on superhydrophobic surface under water has also been studied from both surface microstructure and chemical composition. The main contents are as follows:1. By studying the under water oil-wetting behavior on superhydrophobic surface, we have found that:(a) The underwater oil contact angle on superhydrophobic surface increases from0°to180°with the decay of trapped air and also the reduce of air layer continuity. The decay of trapped air in the grooves of superhydrophobic surface varies the continuity of three-phase contact line, causing the change of the oil wettability on the surface under water. The reduce of air layer continuity on superhydrophobic surface makes the area of oil drops spread decrease, accordingly underwater oil wettability on the surface changes.(b) By comparing with the situation of liquid on the other liquid in air, we find that the wetting behavior with liquid2in liquid1accord with the situation of liquid2on liquid1in air. It indicates that the underwater oil-wetting behavior on superhydrophobic surface can be explained by liquid spread theory.2. The superhydrophobic surface with different surface microstructure is obtained by fabricating organosilane on corroded rough aluminum plat after ultrasonicated for different time. And superhydrophobic surface with different surface chemical composition is prepared by adjusting the proportion of two kinds of organosilane in the process of modification. Then the stability of trapped air on the superhydrophobic surface under water has been investigated. The ultrasonication varies the surface microstructure, which makes the shape of the water/ air interface on the superhydrophobic surface under water change, and then influences the stability of trapped air on the surface; The lower the surface energy of the surface has, the severer the extent to concave down of the water/ air interface forming on the superhydrophobic surface under water is, so the trapped air layer on the surface underwater will more stable.