Wetting gradient induced separation of emulsions: A combined experimental and lattice Boltzmann computer simulation study

TL;DR

This study combines experiments and lattice Boltzmann simulations to explore how wetting gradients can drive emulsion separation, revealing the influence of substrate geometry and wettability on separation efficiency.

Contribution

It provides new insights into the effects of wetting gradients on emulsion separation, combining experimental results with theoretical and simulation analyses.

Findings

Wetting gradients can effectively drive emulsion separation.

Slit geometry enhances separation forces compared to open substrates.

Wettability differences are sufficient for selective emulsion separation.

Abstract

Guided motion of emulsions is studied via combined experimental and theoretical investigations. The focus of the work is on basic issues related to driving forces generated via a step-wise (abrupt) change in wetting properties of the substrate along a given spatial direction. Experiments on binary emulsions unambiguously show that selective wettability of the one of the fluid components (water in our experiments) with respect to the two different parts of the substrate is sufficient in order to drive the separation process. These studies are accompanied by approximate analytic arguments as well as lattice Boltzmann computer simulations, focusing on effects of a wetting gradient on internal droplet dynamics as well as its relative strength compared to volumetric forces driving the fluid flow. These theoretical investigations show qualitatively different dependence of wetting gradient induced forces on contact angle and liquid volume in the case of an open substrate as opposed to a planar channel. In particular, for the parameter range of our experiments, slit geometry is found to give rise to considerably higher separation forces as compared to open substrate.