Generation of Motion of Drops with Interfacial Contact

TL;DR

This paper explores how external vibrations and self-generated noise can induce and control the motion of liquid drops on surfaces, overcoming pinning effects and enabling applications in water and thermal management.

Contribution

It introduces mechanisms for directed and diffusive motion of drops via vibrations and noise, addressing pinning limitations and proposing potential technological applications.

Findings

Vibrations can mitigate surface pinning effects.

Self-generated noise can induce random drop motion.

Directed drift of coalesced drops can be achieved with bias.

Abstract

A liquid drop moves on a solid surface if it is subjected to a gradient of wettability or temperature. However, the pinning defects on the surface manifested in terms of a wetting hysteresis, or first-order nonlinear friction, limit the motion in the sense that a critical size has to be exceeded for a drop to move. The effect of hysteresis can, however, be mitigated by an external vibration that can be either structured or stochastic, thereby creating a directed motion of the drop. Many of the well-known features of rectification, amplification, and switching that are generic to electronics can be engineered with such types of movements. A specific case of interest is the random coalescence of drops on a surface that gives rise to self-generated noise. This noise overcomes the pinning potential, thereby generating a random motion of the coalesced drops. Randomly moving coalesced drops themselves exhibit a directed diffusive flux when a boundary is present to eliminate them by absorption. With the presence of a bias, the coalesced drops execute a diffusive drift motion that can have useful applications in various water and thermal management technologies.