Role of surfactant-induced Marangoni stresses in drop-interface coalescence

TL;DR

This study uses advanced simulations to explore how surfactants influence drop-interface coalescence, revealing the significant role of Marangoni stresses in flow dynamics and interface behavior.

Contribution

The paper introduces a comprehensive 3D simulation approach that accounts for Marangoni stresses, surface diffusion, and sorption kinetics, providing new insights into surfactant effects on coalescence.

Findings

Marangoni stresses critically affect neck reopening dynamics.

Surfactants rigidify the interface, altering flow patterns.

Simulation results align with experimental observations.

Abstract

We study the effect of surfactants on the dynamics of a drop-interface coalescence using full three-dimensional direct numerical simulations. We employ a hybrid interface-tracking/level-set method, which takes into account Marangoni stresses that arise from surface tension gradients, interfacial and bulk diffusion, and sorption kinetic effects. We validate our predictions against the experimental data of Blanchette and Bigioni [Nat. Phys. 2(4):254-257 (2006)] and perform a parametric study that demonstrates the delicate interplay between the flow fields and those associated with the surfactant bulk and interfacial concentrations. The results of this work unravel the crucial role of the Marangoni stresses in the flow physics of coalescence with particular attention paid to their influence on neck reopening dynamics in terms of stagnation-point inhibition, and near-neck vorticity generation. We demonstrate that surfactant-laden cases feature a rigidifying effect on the interface compared to the surfactant-free case, a mechanism that underpins the observed surfactant-induced phenomena.