High-speed directional transport of condensate droplets on superhydrophobic saw-tooth surfaces

Huimin Hou; Xiaomin Wu; Zhifeng Hu; Sihang Gao; Yuxi Wu; Yukai Lin; Liyu Dai; Guisheng Zou; Lei Liu; Zhiping Yuan

doi:10.1016/j.jcis.2023.06.113

High-speed directional transport of condensate droplets on superhydrophobic saw-tooth surfaces

J Colloid Interface Sci. 2023 Nov:649:290-301. doi: 10.1016/j.jcis.2023.06.113. Epub 2023 Jun 17.

Authors

Huimin Hou¹, Xiaomin Wu², Zhifeng Hu¹, Sihang Gao¹, Yuxi Wu³, Yukai Lin¹, Liyu Dai¹, Guisheng Zou³, Lei Liu³, Zhiping Yuan⁴

Affiliations

¹ Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China.
² Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China. Electronic address: wuxiaomin@mail.tsinghua.edu.cn.
³ Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
⁴ Department of Energy and Power Engineering, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China. Electronic address: nikolatesal@bit.edu.cn.

PMID: 37352560
DOI: 10.1016/j.jcis.2023.06.113

Abstract

Hypothesis: Most droplets on high-efficiency condensing surfaces have radii of less than 100 μm, but conventional droplet transport methods (such as wettability-gradient surfaces and structural-curvature-gradient surfaces) that rely on the unbalanced force of three-phase lines can only transport millimeter-sized droplets efficiently. Regulating high-speed directional transport of condensate droplets is still challenging. Therefore, we present a method for condensate droplet transportation, based on the reaction force of the superhydrophobic saw-tooth surfaces to the liquid bridge, the condensate droplets could be transported at high speed and over long distances.

Experiments: The superhydrophobic saw-tooth surfaces are fabricated by femtosecond laser ablation and chemical etching. Condensation experiments and luminescent particle characterization experiments on different surfaces are conducted. Aided by the theoretical analysis, we illustrate the remarkable performance of condensate droplet transportation on saw-tooth surfaces.

Findings: Compared with conventional methods, our method improves the transport velocity and relative transport distance by 1-2 orders of magnitude and achieves directional transport of the smallest condensate droplet of about 2 μm. Furthermore, the superhydrophobic saw-tooth surfaces enable multi-hop directional jumping of condensate droplets, leading to cross-scale increases in transport distances from microns to decimeters.

Keywords: Condensation; Directional droplet transport; Femtosecond laser ablation; Multi-hop jumping; Superhydrophobic surface.