Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Controlling droplet shape and water repellency by Micro-Structured Precision Surface

Akira KAKUTAa and Koshi UMEZAWA

1Department of Mechanical Engineering, Institute of National Colleges of Technology, Tokyo college, 1220-2 Kunugida-machi, Hachioji-shi, TOKYO, JAPAN, 193-0997


Water repellency of solid surfaces is caused by chemical or structural effects. This property control by chemical effects has been applied to a variety of products, but it requires repeated reapplication, which poses a cost issue. For this reason, the attention has been focused on the structural effect of this property manifested by the micro-structured surface. However, it is unclear that the microstructure suitable for achieving the desired water repellency. The purpose of this study is to investigate microstructures suitable for controlling droplet shape and water repellency, and to clear the mechanisms of droplet shape and microstructure. In this study, we fabricated various microstructures on solid surfaces and experimentally evaluated their water repellency when a droplet is dropped on them. In addition, I considered how the shape and arrangement of the microstructure affects the droplet's water repellency. In general, concavo-convex microstructures exhibit water repellency because air enters the concave areas and surface tension is generated between the air and the liquid. The array of microscopic convexities creates concavities and water repellency. When a drop of water is dropped on a linear microstructure, the capillary action continues to occur in the direction along the line, resulting in a large ratio of contact area to droplet volume, which may not fully demonstrate the water repellency effect. Therefore, we predicted that it would be possible to control the surface water repellency by arranging the shape of the micro-cylinders. To evaluate the droplet shape and water repellency of the fabricated microstructures, we investigated the angle of fall and investigated the microstructures suitable for controlling water repellency. Then, I observed the relationship between the surface of the microstructure and the water repellency of the droplets.

Keywords: Structured surface, Droplet shape, Surface property

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