Yielding and flow in adhesive and non-adhesive concentrated emulsions

TL;DR

This study investigates how adhesive and non-adhesive concentrated emulsions respond to shear stress, revealing distinct flow behaviors near yielding and challenging the universality of yielding mechanisms.

Contribution

It provides experimental evidence of different flow behaviors in adhesive versus non-adhesive emulsions, highlighting the impact of interdroplet attraction on yielding.

Findings

Non-adhesive emulsions follow Herschel-Bulkley model with homogeneous flow.

Adhesive emulsions exhibit shear localization and deviate from simple models.

Yielding mechanisms are not universal across different emulsion types.

Abstract

The nonlinear rheological response of soft glassy materials is addressed experimentally by focusing on concentrated emulsions where interdroplet attraction is tuned through varying the surfactant content. Velocity profiles are recorded using ultrasonic velocimetry simultaneously to global rheological data in the Couette geometry. Our data show that non-adhesive and adhesive emulsions have radically different flow behaviors in the vicinity of yielding: while the flow remains homogeneous in the non-adhesive emulsion and the Herschel-Bulkley model for a yield stress fluid describes the data very accurately, the adhesive system displays shear localization and does not follow a simple constitutive equation, suggesting that the mechanisms involved in yielding transitions are not universal.