Particle response during the yielding transition of colloidal glasses

TL;DR

This study uses x-ray scattering to reveal that colloidal glasses undergo a sharp structural transition during yielding, characterized by changes in orientational order and fluctuations, indicating yielding as a dynamic phase transition.

Contribution

It introduces a novel experimental approach combining x-ray scattering and rheology to directly observe microscopic structural changes during yielding in colloidal glasses.

Findings

Sharp transition in orientational order at yielding

Sudden change in intensity fluctuation distributions

Yielding identified as a dynamic transition

Abstract

Yielding is central to the relaxation, flow and fracture of a wide range of soft and molecular glasses, but its microscopic origin remains unclear. Here, we elucidate the yielding of a colloidal glass by using x-ray scattering to monitor the structure factor during the yielding process. We apply a recently introduced combination of small-angle x-ray scattering and rheology to the oscillatory shear, and follow the structure factor during the increasing strain amplitude. Surprisingly, we observe a sharp transition in the orientational ordering of the nearest-neighbor structure upon yielding, in contrast to the smooth variation of the viscoelastic moduli. This transition is accompanied by a sudden change of intensity fluctuations towards Gaussian distributions. We thus identify yielding as a new, dynamically induced transition of the glass in response to the applied shear.