Rate Dependence and Role of Disorder in Linearly Sheared Two-Dimensional Foams

TL;DR

This study investigates how disorder affects the shear flow behavior of two-dimensional foams, revealing that disorder induces rate dependence in velocity profiles, explained by a model based on drag force scaling.

Contribution

It introduces a simple quantitative model linking foam disorder to rate-dependent shear flow through drag force scaling laws.

Findings

Disordered foams show strong rate dependence in velocity profiles.

Ordered foams exhibit rate independence.

A model based on drag force scaling captures both behaviors.

Abstract

The shear flow of two dimensional foams is probed as a function of shear rate and disorder. Disordered foams exhibit strongly rate dependent velocity profiles, whereas ordered foams show rate independence. Both behaviors are captured quantitatively in a simple model based on the balance of the time-averaged drag forces in the foam, which are found to exhibit power-law scaling with the foam velocity and strain rate. Disorder modifies the scaling of the averaged inter-bubble drag forces, which in turn causes the observed rate dependence in disordered foams.