Unidirectional Wetting Surfaces Fabricated by Ultrasonic-Assisted Cutting

Surface microstructures can provide various functionalities, and wettability is a typical surface property that can be controlled by surface textures. Unidirectional wetting properties (UWPs) have been garnering attention as a useful wetting function for industrial functions. Thus, in this study, developing UWPs using surface microstructures has been tested. First, UWPs were calculated with the thermodynamic analysis of contact angle (CA). The analytical results predicted that an increased oblique angle of the microstructures, ω 2 , can increase the advancing CA; the receding CAs could not be calculated, and might exhibit the pinning effect. Ultrasonic-assisted cutting was subsequently employed to fabricate hierarchical microstructures for providing UWPs to a workpiece. Although many burrs have been observed on the edges of the structures, microstructures with different oblique angles, ω 2 =5 ◦ , 10°, and 15°, were fabricated in the designed scales. Finally, the UWPs were verified by measuring the CAs and sliding angles (SAs). The anisotropy of CA hysteresis was indicated in each oblique angle structure, and the anisotropy of SAs was confirmed when ω 2 =10 ◦ and 15°. The retention force ratio of a droplet, r , which indicates the UWPs, was subsequently estimated with two different approaches, and both approaches led a similar value of the attrition rates of r from ω 2 =10 ◦ to 15°.