Investigation of shear banding in three-dimensional foams

TL;DR

This study investigates the flow behavior of three-dimensional aqueous foams, finding no evidence of shear banding and confirming they behave as Herschel-Bulkley fluids under steady shear conditions.

Contribution

The paper provides experimental evidence that 3D aqueous foams do not exhibit shear banding and behave as simple Herschel-Bulkley fluids, contrasting previous findings.

Findings

No observable shear banding in studied foams

Foams flow steadily below predicted critical shear rate

Foams follow Herschel-Bulkley constitutive law

Abstract

We study the steady flow properties of different three-dimensional aqueous foams in a wide gap Couette geometry. From local velocity measurements through Magnetic Resonance Imaging techniques and from viscosity bifurcation experiments, we find that these foams do not exhibit any observable signature of shear banding. This contrasts with two previous results (Rodts et al., Europhys. Lett., 69 (2005) 636 and Da Cruz et al., Phys. Rev. E, 66 (2002) 051305); we discuss possible reasons for this dicrepancy. Moreover, the foams we studied undergo steady flow for shear rates well below the critical shear rate recently predicted (Denkov et al., Phys. Rev. Lett., 103 (2009) 118302). Local measurements of the constitutive law finally show that these foams behave as simple Herschel-Bulkley yield stress fluids.