Singular jets during droplet impact on superhydrophobic surfaces

Xiaoyun Peng; Tianyou Wang; Feifei Jia; Kai Sun; Zhe Li; Zhizhao Che

doi:10.1016/j.jcis.2023.07.186

Singular jets during droplet impact on superhydrophobic surfaces

J Colloid Interface Sci. 2023 Dec:651:870-882. doi: 10.1016/j.jcis.2023.07.186. Epub 2023 Aug 3.

Authors

Xiaoyun Peng¹, Tianyou Wang², Feifei Jia¹, Kai Sun¹, Zhe Li³, Zhizhao Che⁴

Affiliations

¹ State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China.
² State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China; National Industry-Education Platform of Energy Storage, Tianjin University, Tianjin, 300350, China.
³ State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin, 300350, China.
⁴ State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China; National Industry-Education Platform of Energy Storage, Tianjin University, Tianjin, 300350, China. Electronic address: chezhizhao@tju.edu.cn.

PMID: 37573733
DOI: 10.1016/j.jcis.2023.07.186

Abstract

Hypothesis: The impact of droplets is prevalent in numerous applications, and jetting during droplet impact is a critical process controlling the dispersal and transport of liquid. New jetting dynamics are expected in different conditions of droplet impact on super-hydrophobic surfaces, such as new jetting phenomena, mechanisms, and regimes.

Experiments: In this experimental study of droplet impact on super-hydrophobic surfaces, the Weber number and the Ohnesorge number are varied in a wide range, and the impact process is analyzed theoretically.

Findings: We identify a new type of singular jets, i.e., singular jets induced by horizontal inertia (HI singular jets), besides the previously studied singular jets induced by capillary deformation (CD singular jets). For CD singular jets, the formation of the cavity is due to the propagation of capillary waves on the droplet surface; while for HI singular jets, the cavity formation is due to the large horizontal inertia of the toroidal edge during the retraction of the droplet after the maximum spreading. Key steps of the impact process are analyzed quantitatively, including the spreading of the droplet, the formation and the collapse of the spire, the formation and retraction of the cavity, and finally the formation of singular jets. A regime map for the formation of singular jets is obtained, and scaling relationships for the transition conditions between different regimes are analyzed.

Keywords: Cavity retraction; Droplet impact; Singular jet; Superhydrophobic surfaces.