Lifetime of micrometer-sized drops of oil pressed by buoyancy against a planar interface

TL;DR

This study uses Emulsion Stability Simulations to estimate the coalescence time of micrometer-sized oil drops at a water/oil interface, highlighting the importance of repulsive barriers and drop deformability.

Contribution

It introduces a simulation approach considering various forces and deformation states to better understand drop coalescence dynamics at interfaces.

Findings

Repulsive potential barriers significantly affect coalescence times.

Experimental data align with models assuming negligible barriers and non-deformable drops.

Drop approach dynamics involve combined Stokes and Taylor tensors.

Abstract

Emulsion Stability Simulations (ESS) are used to estimate the coalescence time of one drop of hexadecane pressed by buoyancy against a planar water/hexadecane interface. In the present simulations the homophase is represented by a big drop of oil at least 500 times larger than the approaching drop ($1\,\mu$m to $10\,\mu$m). Both deformable and non-deformable drops are considered along with six different diffusion tensors. In each case van der Waals, electrostatic, steric and buoyancy forces are taken into account. The coalescence times are estimated as the average of 1000 random walks. It is found that the repulsive potential barrier has a significant influence in the results. The experimental data can only be reproduced assuming negligible repulsive barriers, as well as non-deformable drops that move with a combination of Stokes and Taylor tensors as they approach the interface.