Relaxing in foam

TL;DR

This paper studies the mechanical behavior of aqueous foam, linking microscopic bubble dynamics to macroscopic rheology, and introduces a new rheological measurement method involving superposed step-strain.

Contribution

It reveals the linear rheology of foam at rest despite coarsening and introduces a novel rheological technique to analyze foam under flow conditions.

Findings

Foam exhibits linear rheology at rest despite coarsening.

Shear-induced and coarsening-induced rearrangements compete under flow.

A new rheological method with superposed step-strain effectively captures foam dynamics.

Abstract

We investigate the mechanical response of an aqueous foam, and its relation to the microscopic rearrangement dynamics of the bubble-packing structure. At rest, even though the foam is coarsening, the rheology is demonstrated to be linear. Under flow, shear-induced rearrangements compete with coarsening-induced rearrangements. The macroscopic consequences are captured by a novel rheological method in which a step-strain is superposed on an otherwise steady flow.