The Size Effect on Contact Angles and Dynamic Behaviors of Droplets on Microcolumn and Microstrip Array Surfaces

The hydrophobicity of biomimetic hydrophobic surfaces exhibits a correlation with droplet relative dimension. Nevertheless, the droplet relative dimension-dependent wettability, contact angles, dynamic droplet bouncing behaviors need to be further investigated. This article focuses on the size effect of droplet relative dimension on the contact angles and dynamic behaviors of regular microcolumn and microstrip array surfaces, which were directly machined by low-speed wire electrical discharge machining (WEDM-LS). Specifically, the contact angles are measured with droplet relative dimension in a range from 29.8 to 298 on various structured surfaces. The dynamic droplet bouncing tests are based on a coincident falling height of 10 mm. The period time is also gradually shortened with the decreasing of droplet relative dimension, which indicated that the droplets with relatively larger relative dimensions are more difficult to overcome the adhesion of arrayed structures. Meanwhile, when the droplet relative dimension exceeded a critical value, the droplet failed to separate from the substrate due to the interface adhesion and the period time would be also shortened which attributed to less time consumption for the insufficient capillary force compared with the gravity.