Investigations On Design And Micro-Milling Of Micro-Textured Hydrophobic Surface

Hydrophobic surface has the abilities of self-cleaning, drag reduction and anti-wear properties, which can bring great convenience to people and can create great momentum for human development when the technologies are mature and hydrophobic surface can be produced massively. Micro-textures, nano-structure and low surface energy materials make the solid surface hydrophobic. With the researches on mechanism of the micro processing, the improving accuracy of milling and turning, as well as the cutter size decreasing, it becomes possible to research the hydrophobicity of micro-textures which can be processed by mechanical micro-cutting technology. Contact angle is an important index of hydrophobicity. In order to study the micro-textures affecting the contact angle, based on the model of Young, Wenzel and Cassie-Baxter, the prediction model for contact angle of hydrophobic surface based on minimum Gibbs free energy have be proposed. The micro-textures on hydrophobic surface are finished by micro-cutting operations. Theoretical analysis and testes are combined to study the effect of micro-textures on contact angle.Firstly, based on the model of Young used for smooth surface, the models of Wenzel and Cassie-Baxter used for rough surface, the prediction model for contact angle of hydrophobic surface based on minimum Gibbs free energy is proposed. The model for contact angle prediction is then modified by considering the influence of inclined-walls on the contact line between gas-liquid. The effects of hydrophobic surface material properties and geometrical parameters on contact angle are analyzed based on the modified model. The results show that, under the same condition of machined micro-textures, the contract angle on the hydrophobic surface root is larger than that on the hydrophilic one. Besides, for the Cassie-Baxter model, the larger radio between the width of groove and the width of convex is, the larger contract angle is.Then, the microgroove, the microarray, the inclined-wall microgroove as well as inclined-wall microarray are designed and manufactured by using micro-milling methods. The micro-milling processes are studied and the contact angles are measured.Finally, Theoretical analysis and experimental researches are made to study the influences of surface parameters of microgroove and microarray on contact angles. Based on the Young model for smooth surface and the models of Wenzel and Cassie-Baxter for rough surface, the novel formulas used for microgroove and microarray surfaces are proposed in this research. Microgroove and microarray surfaces generated with micro end-milling operations with milling cutter diameter 0.1mm are investigated. The contact angles on machined surfaces are measured and analyzed. The results show that both microgroove and microarray machined surface have positive effect on the improvement of hydrophobic properties. The contact angle increases with the increase of the distance of micro-structures while with the decrease of micro-texture dimensions. The contract angles of water droplets on the machined surface at the vertical direction are different from those at the paralleled direction of microgroove, and they influence each other. The contact angles for water droplet on the microgroove surface are more stable than those on the microarray surface. However, the contact angle for water droplet on the microarray surface is larger than that on the microgroove surface. The water droplet on machined microarray surface is nearly spherical. Comparing with the microgroove micro-texture and the microarray micro-texture, the existence of inclined-wall can increase the contact angle, and then to enhance the instability of water on the surface of micro-textures. Water droplets are more likely to enter the micro-texture inside and to present the Wenzel model. Besides, the existence of the inclined-wall makes the influence of the dimensional parameters insignificant to the contact angles.