Phase Transitions of Oscillating Droplets on Horizontally Vibrating Substrates

TL;DR

This study uses simulations to explore how droplets oscillate on vibrating surfaces, revealing phase transitions, stability conditions, and breakup mechanisms relevant for natural phenomena and technological applications.

Contribution

The paper provides a comprehensive simulation-based analysis of droplet oscillation phases and transitions on vibrating substrates, including instability growth and droplet breakup.

Findings

Identified distinct oscillation phases and their transitions.

Determined instability growth rates leading to droplet breakup.

Characterized droplet states via particle contact analysis.

Abstract

Droplet deformations caused by substrate vibrations are ubiquitous in nature and highly relevant for applications such as microreactors and single-cell sorting. The vibrations can induce droplet oscillations, a fundamental process that requires an in-depth understanding. Here, we report on extensive many-body dissipative particle dynamics simulations carried out to study the oscillations of droplets of different liquids on horizontally vibrating substrates, covering a wide range of vibration frequencies and amplitudes as well as substrate wettability. We categorize the phases observed for different parameter sets based on the capillary number and identify the transitions between the observed oscillation phases, which are characterized by means of suitable parameters, such as the angular momentum and vorticity of the droplet. The instability growth rate for oscillation phase II, which leads to highly asymmetric oscillations and eventual droplet breakup, is also determined. Finally, we characterize the state of the droplet for the various scenarios by means of the particle-particle and particle-substrate contacts. We find a steady-state scenario for phase I, metastable breathing modes for phase II, and an out-of-equilibrium state for phase III. Thus, we anticipate that this study provides much needed insights into a fundamental phenomenon in nature with significant relevance for applications.