Non-coalescence of sessile drops from different but miscible liquids: Hydrodynamic analysis of the twin drop contour as self stabilizing, traveling wave

TL;DR

This paper investigates why sessile drops from different but miscible liquids sometimes do not fuse immediately, instead forming a stable twin-drop configuration stabilized by Marangoni flows, supported by experimental and hydrodynamic analysis.

Contribution

It introduces a hydrodynamic model explaining the non-coalescence of miscible drops through a self-stabilizing traveling wave mechanism.

Findings

The twin drop configuration is stabilized by surface tension gradients.

Experimental data confirms the hydrodynamic model predictions.

The model accurately describes the observed non-coalescence behavior.

Abstract

Capillarity always favors drop fusion. Nevertheless sessile drops from different but completely miscible liquids often do not fuse instantaneously upon contact. Rather, intermediate non-coalescence is observed. Two separate drop bodies, connected by a thin liquid neck move over the substrate. Supported by new experimental data a thin film hydrodynamic analysis of this state is presented. Presumably advective and diffusive volume fluxes in the neck region establish a localized and temporarily stable surface tension gradient. This induces a local surface (Marangoni) flow that stabilizes a traveling wave i.e., the observed moving twin drop configuration. The theoretical predictions are in excellent agreement with the experimental findings.