Velocity Profiles in Slowly Sheared Bubble Rafts

TL;DR

This study investigates velocity profiles in slowly sheared bubble rafts, revealing coexistence of flowing and jammed states, with flow driven by nonlinear rearrangements and average velocities stabilizing after few events.

Contribution

It provides new insights into the connection between short-time bubble rearrangements and long-time average velocity profiles in bubble rafts.

Findings

Velocity profiles fluctuate during individual rearrangements

A smooth average velocity profile emerges after few events

Flow behavior resembles that of 3D foams and emulsions

Abstract

Measurements of average velocity profiles in a bubble raft subjected to slow, steady-shear demonstrate the coexistence between a flowing state and a jammed state similar to that observed for three-dimensional foams and emulsions [Coussot {\it et al,}, Phys. Rev. Lett. {\bf 88}, 218301 (2002)]. For sufficiently slow shear, the flow is generated by nonlinear topological rearrangements. We report on the connection between this short-time motion of the bubbles and the long-time averages. We find that velocity profiles for individual rearrangement events fluctuate, but a smooth, average velocity is reached after averaging over only a relatively few events.