Soft wetting: Substrate softness- and time-dependent droplet/bubble adhesion

Kaiyuan Chen; Juan Li; Chuanqi Wei; Alexander Oron; Yanguang Shan; Youhua Jiang

doi:10.1016/j.jcis.2024.02.037

Soft wetting: Substrate softness- and time-dependent droplet/bubble adhesion

J Colloid Interface Sci. 2024 May 15:662:87-98. doi: 10.1016/j.jcis.2024.02.037. Epub 2024 Feb 8.

Authors

Kaiyuan Chen¹, Juan Li², Chuanqi Wei³, Alexander Oron⁴, Yanguang Shan⁵, Youhua Jiang⁶

Affiliations

¹ School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China; Department of Mechanical Engineering, Guangdong Technion - Israel Institute of Technology, Shantou, Guangdong 515063, China.
² Department of Mechanical Engineering, Guangdong Technion - Israel Institute of Technology, Shantou, Guangdong 515063, China; Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
³ Department of Mechanical Engineering, Guangdong Technion - Israel Institute of Technology, Shantou, Guangdong 515063, China.
⁴ Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
⁵ School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China. Electronic address: shan@usst.edu.cn.
⁶ Department of Mechanical Engineering, Guangdong Technion - Israel Institute of Technology, Shantou, Guangdong 515063, China; Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel; Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion - Israel Institute of Technology, Shantou, Guangdong 515063, China. Electronic address: youhua.jiang@gtiit.edu.cn.

PMID: 38340517
DOI: 10.1016/j.jcis.2024.02.037

Abstract

Hypothesis: The droplet/bubble adhesion characteristics depend on the length of the droplet/bubble three-phase contact line. Since the deformation caused by the liquid-gas interfacial tension on the soft substrate, referred as to the wetting ridge, retards contact line spreading and retraction, we conjecture that the droplet/bubble adhesion characteristics depend also on the substrate softness.

Experiments: Soft substrates with various shear moduli are prepared and characterized by the spreading and receding dynamics of water droplets and underwater bubbles. Snap-in and normal adhesion forces of droplets/bubbles on such soft substrates are directly measured along with the visualized droplet/bubble shape profiles.

Findings: The droplet/bubble snap-in force, which corresponds to the short-time spreading dynamics, decreases with a decrease in the substrate shear modulus because of the retarded contact line spreading. The droplet maximal adhesion force on a soft substrate can be counterintuitively either smaller or larger than its counterpart on the rigid substrate depending on different dwelling times, i.e., the droplet/bubble-substrate contact time before droplet/bubble-substrate separation. The former is attributed to the retarded contact line spreading, whereas the latter is attributed to the retarded contact line retraction. The substrate softness- and dwelling time-dependent droplet/bubble adhesion reported in this study will benefit various applications related to soft substrates.

Keywords: Adhesion; Bubble; Contact line; Droplet; Soft wetting.