Note on the pairwise interactions of surfactant-covered drops in a uniform electric field

TL;DR

This paper investigates how insoluble surfactants influence the pairwise electrohydrodynamic interactions of drops in a uniform electric field, revealing that surfactants weaken flows and can prevent coalescence under certain conditions.

Contribution

It combines numerical boundary integral simulations and analytical theory to analyze surfactant effects on drop interactions in electric fields, a novel approach for this problem.

Findings

Surfactants weaken electrohydrodynamic flows.

Surfactants make dielectrophoretic interactions more prominent.

Nondiffusing surfactants can prevent drop coalescence.

Abstract

We study the effect of surfactant on the pairwise interactions of drops in an applied uniform DC electric field using a combination of numerical simulations based on a boundary integral formulation and an analytical theory assuming small drop deformations. The surfactant is assumed to be insoluble in the bulk-phase fluids. We show that the surfactant weakens the electrohydrodynamic flow and thus dielectrophoretic interactions play more prominent role in the dynamics of surfactant-covered drops compared to clean drops. If drop conductivity is the same as the suspending fluid, a nondiffusing surfactant can arrest the drops' relative motion thereby effectively preventing coalescence.