Vorticity Alignment and Negative Normal Stresses in Sheared Attractive Emulsions

TL;DR

This study investigates the rheological behavior of attractive emulsions near the colloidal glass transition, revealing vorticity alignment, negative normal stresses, and shear-thinning properties through combined rheometry and microscopy.

Contribution

It uncovers the relationship between vorticity alignment, negative normal stresses, and shear behavior in attractive emulsions, highlighting universal features in complex fluids.

Findings

Viscosity drops then plateaus and decays with shear rate

First normal stress difference becomes negative during constant viscosity

Cylindrical flocs align along vorticity and exhibit log-rolling movement

Abstract

Attractive emulsions near the colloidal glass transition are investigated by rheometry and optical microscopy under shear. We find that (a) the apparent viscosity \eta drops with increasing shear rate, then remains approximately constant in a range of shear rates, then continues to decay; (b) the first normal stress difference N1 transitions sharply from nearly zero to negative in the region of constant shear viscosity; (c) correspondingly, cylindrical flocs form, align along the vorticity and undergo a log-rolling movement. An analysis of the interplay between steric constraints, attractive forces, and composition explains this behavior, which seems universal to several other complex systems.