How Crystals Flow: Work Hardening in Colloidal Crystals

Irreversible (plastic) deformation of crystalline materials is mediated by the nucleation and motion of topological line defects known as dislocations. The complex collective behavior of these defects gives rise to intricate metastable dislocation networks. However, directly resolving deformation processes in atomic solids remains extremely challenging, limiting our ability to connect macroscopic irreversible flow with the underlying defect dynamics.

In this talk, I will discuss the plastic flow of colloidal crystals, ordered self-assembly of micron-sized hard spheres suspended in a fluid. Their large particle size enables direct visualization of deformation in real-time and at the single-particle level using confocal microscopy. We show that hard-sphere colloidal crystals exhibit work hardening, becoming increasingly resistant to deformation as plastic strain accumulates. Their strength increases with dislocation density and, remarkably, ultimately follows the classical Taylor scaling originally developed to describe work hardening in metals. This striking resemblance between colloidal and atomic crystals, despite the simplicity of hard-sphere interactions and the many orders of magnitude difference in particle size and elastic modulus, demonstrates the universality of work hardening and highlights the potential of colloidal crystals to reveal how the collective dynamics of dislocations give rise to the flow of crystalline matter.