Direct observation of hydrodynamic instabilities in driven non-uniform colloidal dispersions

TL;DR

This study observes and analyzes hydrodynamic instabilities in driven colloidal dispersions, revealing how gravitational forces induce pattern formation and mixing, with implications for various scientific fields.

Contribution

It provides the first detailed particle-level observation and theoretical analysis of Rayleigh-Taylor-like instabilities in colloidal systems under gravity.

Findings

Identification of a gravity-driven instability mechanism

Correlation between fluctuations and pattern formation

Predictive linear stability theory for mixing conditions

Abstract

A Rayleigh-Taylor-like instability of a dense colloidal layer under gravity in a capillary of microfluidic dimensions is considered. We access all relevant lengthscales with particle-level microscopy and computer simulations which incorporate long-range hydrodynamic interactions between the particles. By tuning the gravitational driving force, we reveal a mechanism whose growth is connected to the fluctuations of specific wavelengths, non-linear pattern formation and subsequent diffusion-dominated relaxation. Our linear stability theory captures the initial regime and thus predicts mixing conditions, with important implications for fields ranging from biology to nanotechnology.