Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneities

TL;DR

This study links the macroscopic creep behavior of colloidal glasses to microscopic particle dynamics, revealing how localized and growing dynamical heterogeneities influence flow under stress.

Contribution

It provides a quantitative connection between microscopic heterogeneities and macroscopic creep response in amorphous solids, using experiments and simulations.

Findings

Dynamical heterogeneities remain localized during creep but grow during steady flow.

Microscopic particle displacements are proportional to macroscopic strain.

Active regions correlate with the transition from creep to flow.

Abstract

Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely col- loidal glasses, to external forces. Using confocal microscopy and computer simulations, we establish a quantitative link between the macroscopic creep response and the microscopic single-particle dy- namics. We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow. These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared dis- placement of the individual particles, and the fraction of active regions. Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.