Effect of pre-wetting on the wettability of laser ablated Al superhydrophobic/superhydrophilic surface
Zheng Zhixia1, Yang Huan2     
1. School of Mechanical and Electrical Engineering, Putian University, Putian, Fujian 351100, China;
2. Sino-German College of Intelligent Manufacturing, Shenzhen Technology University, Shenzhen, Guangdong 518118, China

Overview:The special wettabilities of solid surfaces have important roles in self-cleaning, anti-corrosion, anti-icing, resistance reduction, anti-bacterial, oil-water separation, oil-water-gas separation, and so on. In recent years, the research on special wettability has gradually developed from solid/water two-phase to solid/water/oil/air four-phase systems. It is of great significance to study the special wettability of superhydrophobic/superhydrophilic surface in water, oil, and the behavior of bubbles on it. This type of surface can be applied to oil-water separation, underwater bubble location and collection, liquid transportation and so on. By controlling the laser processing parameters, such as wavelength, pulse width, frequency, and scanning speed, the micro-nano scale structure with special wettability can be fabricated on the surfaces of various materials. In this paper, micro-nano scale structures on aluminum substrates were fabricated by a pulsed fiber laser, and superhydrophobic surfaces were prepared with a subsequent chemical modification. With a designed pattern, a secondary laser processing was conducted to remove the chemical layer on the superhydrophobic surface, then a superhydrophobic/superhydrophilic mixed surface was achieved. The effect of pre-wetting on the special wettability and the wetting stability of the samples were studied. The results showed that, for the superhydrophobic/superhydrophilic mixed surface, the wetting behaviors in water, in oil, and the corresponding behaviors of bubbles were closely related to wettability in air. The superhydrophobic surface exhibited superoleophilicity and superaerophilicity in water, and the superhydrophilic surface exhibited superoleophobicity and superaerophobicity in water. Besides, in oil, both superhydrophobic and superhydrophilic surfaces exhibited superaerophobicity and superhydrophobicity. The pre-wetting could influence the wettability in liquid. After pre-wetting with an oil, the superhydrophobic and superhydrophilic surface exhibited both superaerophobicity and superoleophilicty in water. Moreover, after pre-wetting with water, the superhydrophobic surface is superaerophobicity and superhydrophobicity in oil, while the superhydrophilic surface is superaerophobicity and superhydrophilicity. The stability test of the wettability for the superhydrophobic/superhydrophilic mixed surface shows that the wettability can be kept stable for a long time by drying and sealing under normal temperature. It is of great significance to study the underwater and under oil wettabilities of the superhydrophobic/superhydrophilic mixed surface, as well as the influence of pre-wetting on the wettability in oil and water, for controlling oil/water/gas and promoting the application of super hydrophobic/superhydrophilic mixed surfaces.

Supported by the Natural Science Foundation of Fujian (2017H0032) and the Open Project Program of Laser Precision Machining Engineering Technology Research Center of Fujian Province (2017JZA001)