Experimental measurements of stress redistribution in flowing emulsions

TL;DR

This study investigates how local droplet rearrangements in dense emulsions affect nearby stresses, revealing anisotropic quadrupolar stress redistribution patterns that support rheological theories of amorphous materials.

Contribution

It provides direct experimental evidence of stress redistribution patterns around rearrangements in dense emulsions, advancing understanding of their rheological behavior.

Findings

Rearrangements cause quadrupolar stress changes in neighboring droplets.

Stress redistribution becomes more anisotropic at higher area fractions.

Results support theories linking local rearrangements to stress changes in amorphous materials.

Abstract

We study how local rearrangements alter droplet stresses within flowing dense quasi-two-dimensional emulsions at area fractions $\phi \geq 0.88$. Using microscopy, we measure droplet positions while simultaneously using their deformed shape to measure droplet stresses. We find that rearrangements alter nearby stresses in a quadrupolar pattern: stresses on neighboring droplets tend to either decrease or increase depending on location. The stress redistribution is more anisotropic with increasing $\phi$. The spatial character of the stress redistribution influences where subsequent rearrangements occur. Our results provide direct quantitative support for rheological theories of dense amorphous materials that connect local rearrangements to changes in nearby stress.