Dilatancy of Shear Transformations in a Colloidal Glass

TL;DR

This study uses colloidal glasses to directly observe shear transformations, revealing that local free volume increase precedes shear events and that dilatancy ability influences their occurrence, providing insights into amorphous plasticity.

Contribution

It provides the first real-space observation of shear transformations in colloidal glasses, highlighting the role of dilatancy and free volume dynamics in amorphous plasticity.

Findings

Local free volume temporarily increases before shear transformations.

Shear transformations depend on the dilatancy ability of regions.

Shear transformations show no memory of initial free volume.

Abstract

Shear transformations, as fundamental rearrangement events operating in local regions, hold the key of plastic flow of amorphous solids. Despite their importance, the dynamic features of shear transformations are far from clear. Here, we use a colloidal glass under shear as the prototype to directly observe the shear transformation events in real space. By tracing the colloidal particle rearrangements, we quantitatively determine two basic properties of shear transformations: local shear strain and dilatation (or free volume). It is revealed that the local free volume undergoes a significantly temporary increase prior to shear transformations, eventually leading to a jump of local shear strain. We clearly demonstrate that shear transformations have no memory of the initial free volume of local regions. Instead, their emergence strongly depends on the dilatancy ability of these regions, i.e., the dynamic creation of free volume. More specifically, the particles processing the high dilatancy ability directly participate in subsequent shear transformations. These results experimentally support the Argon's statement about the dilatancy nature of shear transformations, and also shed insight into the structural origin of amorphous plasticity.