Capillary imbibition of monodisperse emulsions in confined microfluidic channels

TL;DR

This study explores how monodisperse emulsions imbibe into confined microfluidic channels, revealing complex droplet dynamics, fluctuations, and the influence of confinement on flow behavior using a combination of experiments and theoretical modeling.

Contribution

It introduces a detailed analysis of droplet motion and fluctuations during imbibition in microchannels, supported by a macroscopic transport model and particle interaction theory.

Findings

Tightly confined droplets move slower than suspension average.

Weaker confinement causes faster droplet motion and unstable high-concentration regions.

Linear transport equations effectively describe suspension dynamics.

Abstract

We investigate imbibition of a monodisperse emulsion into a low-aspect ratio microfluidic channel with the height h comparable to the droplet diameter d. For confinement ratio d/h = 1.2, the tightly confined disk-like droplets in the channel move more slowly compared to the average suspension velocity. Behind the meniscus that drives the imbibition, there is a droplet-free region, separated from the suspension region by a sharp concentration front. The suspension exhibits strong droplet density and velocity fluctuations, but on average, the suspension domain remains uniform. For weaker confinement, d/h = 0.65, the spherical droplets move faster than the average suspension flow, resulting in the formation of a dynamically unstable high-concentration region near the meniscus. We describe the macroscopic suspension dynamics using linear transport equations for the particle-phase flux and suspension flux that are driven by the local pressure gradient. A dipolar particle interaction model explains the observed large density and velocity fluctuations in terms of the dynamics of elongated particle clusters with different orientations.