Viscous fingering at ultralow interfacial tension

TL;DR

This study investigates viscous fingering in a colloid-polymer mixture with ultralow interfacial tension, using advanced microscopy and simulations to understand interface fluctuations, curvature effects, and wall wetting.

Contribution

It provides new experimental insights into viscous fingering at ultralow surface tension and combines microscopy with simulations for comprehensive analysis.

Findings

Thermal interface fluctuations influence fingering patterns.

3D imaging reveals curvature-flow interactions.

Complete wall wetting alters instability dynamics.

Abstract

We experimentally study the viscous fingering instability in a fluid-fluid phase separated colloid-polymer mixture by means of laser scanning confocal microscopy and microfluidics. We focus on three aspects of the instability. (i) The interface between the two demixed phases has an ultralow surface tension, such that we can address the role of thermal interface fluctuations. (ii) We image the interface in three dimensions allowing us to study the interplay between interface curvature and flow. (iii) The displacing fluid wets all walls completely, in contrast to traditional viscous fingering experiments, in which the displaced fluid wets the walls. We also perform lattice Boltzmann simulations, which help to interpret the experimental observations.