Vibrating water droplets to dry hydrophobic surfaces

Removing water from surfaces is no easy task. Water is a polar molecule, and as a result, it tends to stick to most surfaces. Hydrophobic surfaces designed to repel water do exist, but even these may need some help to fully dry. When these surfaces are horizontal, the water is repelled but not removed; instead, it sits on top of the surface in droplets.

Sun et al. studied a method for removing these droplets from superhydrophobic surfaces using vibrations. They performed experiments and developed a theoretical model to determine the most efficient conditions for droplet removal.

“We are particularly interested in simplifying this complex problem to reveal the key physics,” said author Kai Sun. “To achieve this, we established a mass-spring-damper theoretical model, which is usually used in vibration mechanics rather than in fluid mechanics studies, and successfully explained how a droplet could detach from a vibrating superhydrophobic surface.”

The researchers found the droplets’ energy must exceed the surface adhesion energy to detach the droplets from the surface. This can be achieved efficiently by vibrating the surface at its resonant frequency, with the minimum required amplitude provided by their theoretical model.

The team is planning to broaden their results by examining alternative vibration patterns. They hope this technique will benefit a wide range of fields, from heat transfer to microfluidics.

“In the present work, for simplicity, we only applied sinusoidal-type vibration on the substrate,” said Sun. “In future works, exploring the optimal profile of substrate vibration for improved rate and efficiency of droplet detachment is highly warranted.”

Source: “Vibration-induced detachment of droplets on superhydrophobic surfaces,” by Kai Sun, Lingyun Shu, Feifei Jia, Zhe Li, and Tianyou Wang, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0089087 .