Fluidization and wall slip of soft-glassy materials by controlled surface roughness

TL;DR

This study investigates how controlled surface roughness in microfluidic channels influences the flow and fluidization of soft-glassy materials, revealing a scaling law and the role of groove density in fluidization.

Contribution

It provides a quantitative analysis of how surface roughness patterning affects soft-glassy material flow, supported by experiments and simulations, introducing a scaling law for fluidization.

Findings

Roughness-induced fluidization can be tuned by groove width and separation.

A simple scaling law relates fluidization to groove density.

Numerical simulations link fluidization to plastic rearrangements.

Abstract

The motion of soft-glassy materials (SGM) in a confined geometry is strongly impacted by surface roughness. However, the effect of the spatial distribution of the roughness remains poorly understood from a more quantitative viewpoint. Here we present a comprehensive study of concentrated emulsions flowing in microfluidic channels, one wall of which is patterned with micron-size equally spaced grooves oriented perpendicularly to the flow direction. We show that roughness-induced fluidization can be quantitatively tailored by systematically changing both the width and separation of the grooves. We find that a simple scaling law describes such fluidization as a function of the density of grooves, suggesting common scenarios for droplet trapping and release. Numerical simulations confirm these views and are used to elucidate the relation between fluidization and the rate of plastic rearrangements.