Self-Organized Velocity Pulses of Dense Colloidal Suspensions in Microchannel Flow

TL;DR

This study uses numerical simulations to explore how dense colloidal suspensions in microchannels form upstream-traveling velocity pulses, highlighting the roles of friction and force chains in pulse formation and transitions.

Contribution

It introduces a phenomenological continuum model explaining the formation and dynamics of velocity pulses in dense colloidal flows, linking microscopic interactions to macroscopic flow patterns.

Findings

Velocity pulses travel upstream in the microchannel.

Colloid-wall friction is crucial for pulse formation.

Different flow regimes include solitary jams and periodic pulses.

Abstract

We present a numerical study of dense colloidal suspensions in pressure-driven microchannel flow in two dimensions. The colloids are modeled as elastic and frictional spheres suspended in a Newtonian fluid, which we simulate using the method of multi-particle collision dynamics. The model reproduces periodic velocity and density pulse trains, traveling upstream in the microchannel, which are found in experiments conducted by L. Isa et al. [Phys. Rev. Lett. 102, 058302 (2009)]. We show that colloid-wall friction and the resultant force chains are crucial for the formation of these pulses. With increasing colloid density first solitary jams occur, which become periodic pulse trains at intermediate densities and unstable solitary pulses at high densities. We formulate a phenomenological continuum model and show how these spatio-temporal flow and density profiles can be understood as homoclinic and periodic orbits in traveling-wave equations.