Effect of surface structures on droplet dynamics

Abstract: Dynamic wetting phenomena are present in many everyday situations where liquids interact with surfaces. Understanding and controlling the dynamics of droplets wetting solid surfaces is important in various applications such as boiling and condensation heat transfer, printing and coating, and microfluidic processes. However, modeling their dynamics is not easy because they are multiscale systems in which the advancing or receding of a nanoscale-thick contact line is linked to the behavior of the entire millimeter-scale droplet. In the Thermal Energy Engineering lab (TEEL) at the University of Tokyo, together with the collaborators, we have been investigating the droplets spreading and moving on solid surfaces, where the non-equilibrium nature of energy dissipation at the contact line becomes evident. On a partially wetting solid surface, when capillary forces drive droplet spreading, the advancement of the contact line is governed by viscous forces, inertial forces, or contact-line friction. Through experiments, we demonstrated that the dominant physical mechanisms can be switched by tuning droplet properties, surface microstructure [1], or applied electric field [2]. We modeled and reproduced these experiments using a phenomenological parameter that quantifies the contact-line friction coefficient and mapped a phase diagram of dominant physical factors in a dimensionless parameter space [7]. With the knowledge, we realized anisotropic wetting and droplet transport by taking advantage of the fact that the dynamic behavior of droplets can be controlled through solid surfaces when contact line friction is dominant [3,4]. Furthermore, in our recent experiments on droplet oscillation [5] and droplet sliding [6] on solid surfaces functionalized with various self-assembled monolayers (SAMs), we observed that nanoscale surface chemistry and morphology significantly influence contact-line dynamics.

References

1. J. Wang, M. Do-Quang, J. J. Cannon, F. Yue, Y. Suzuki, G. Amberg, J. Shiomi, “Surface structure determines dynamic wetting”, Sci. Rep. 5, 1-7 (2015).

2. S. Nita, M. Do-Quang, J. Wang, Y-C. Chen, Y. Suzuki, G. Amberg, J. Shiomi, “Electrostatic cloaking of surface structure for dynamic wetting”, Sci. Adv. 3, e1602202 (2017).

3. Y. Lee, N. Matsushima, S. Yada, S. Nita, T. Kodama, G. Amberg, J. Shiomi, “Revealing how topography of surface microstructures alters capillary spreading”, Sci. Rep. 9, 1-11 (2019).

4. Y. Lee, G. Amberg, J. Shiomi, “Vibration sorting of small droplets on hydrophilic surface by asymmetric contact-line friction”, PNAS Nexus1, pgac027 (2022).

5. Y. Li, Y. Lee, S. Fujikawa, J. Shen, S. Sasaki, M. Matsuzaki, N. Matsui, T. Hosomi, T. Yanagida, J. Shiomi, “Ultra-slippery hydrophilic surfaces by hybrid monolayers”, ACS Appl. Mater. Interfaces 16, 63039-63048 (2024).

6. J. Shen, Y. Lee, Y. Li, S. Zaleski, G. Amberg, J. Shiomi, “Dynamic hysteresis of an oscillatory contact line”, J. Fluid Mech. 1000, A34 (2024).

7. J. Shen, Y. Lee, J. Shiomi, “Phenomenological contact line friction coefficient”, Droplet 4, e70030 (2025).

Bio: Junichiro Shiomi is Professor in Institute of Engineering Innovation and Department of Mechanical Engineering, School of Engineering, the University of Tokyo. He received B.E. from Tohoku University, and Ph. D. from Royal Institute of Technology (KTH), Sweden. Leading the Thermal Energy Engineering Lab, he has been pursuing research to advance thermal management, waste heat recovery, and energy harvesting technologies based on nano-to-macro innovation in materials, structures, and systems. Prof. Shiomi is Fellow of Japan Society of Mechanical Engineers, Member of Science Council of Japan, and Member of Engineering Academy of Japan. He serves as an Associate Editor of Nanoscale and Microscale Thermophysical Engineering. He is a recipient of the Zeldovich Medal from the Committee on Space Research, the Commendation for Science and Technology by the Minister of Educational, Culture, Sports, Science and Technology, the Academic award of Heat Transfer Society of Japan, the Academic Award of Thermoelectric Society of Japan, the JSPS Award, and the Nukiyama Memorial Award.