Shear induced drainage in foamy yield-stress fluids

TL;DR

This study uses MRI to explore how shear forces induce drainage in foamy yield-stress fluids, revealing a viscous behavior of the interstitial fluid and the role of foam films in trapping liquid, which differs from classical models.

Contribution

It demonstrates the strong coupling between shear-induced interstitial flow and drainage, highlighting the impact of foam films on liquid trapping and flow behavior.

Findings

Shear causes rapid drainage in foamy yield-stress fluids.

Interstitial fluid behaves as a viscous fluid under shear.

Foam films trap interstitial liquid, arresting drainage.

Abstract

Shear induced drainage of a foamy yield stress fluid is investigated using MRI techniques. Whereas the yield stress of the interstitial fluid stabilizes the system at rest, a fast drainage is observed when a horizontal shear is imposed. It is shown that the sheared interstitial material behaves as a viscous fluid in the direction of gravity, the effective viscosity of which is controlled by shear in transient foam films between bubbles. Results provided for several bubble sizes are not captured by the R^2 scaling classically observed for liquid flow in particulate systems, such as foams and thus constitute a remarkable demonstration of the strong coupling of drainage flow and shear induced interstitial flow. Furthermore, foam films are found to be responsible for the unexpected arrest of drainage, thus trapping irreversibly a significant amount of interstitial liquid.