Variations of the Herschel–Bulkley exponent reflecting contributions of the viscous continuous phase to the shear rate-dependent stress of soft glassy materials

Abstract

We explore the flow behavior of concentrated emulsions for which the viscosity of the continuous phase can be significantly varied by changing the temperature. The exponents obtained by fitting the shear rate-dependent stress with the popular Herschel–Bulkley (HB) model display a systematic dependence on the viscosity of the continuous phase, revealing that viscous dissipation via the suspending fluid cannot be neglected in the description of the flow behavior of soft glassy systems. We thus propose a simple constitutive equation that accounts for three distinct dissipation mechanisms: elastic, plastic, and viscous dissipation. This three component model describes the flow behavior of soft glassy materials as accurately as the HB model, albeit maintaining a clear physical insight into the dissipation processes at work.