Short-ranged attractions in jammed liquids: How cooling can melt a glass

TL;DR

This paper presents a model explaining how short-range attractions in dense colloidal suspensions lead to unusual relaxation behaviors and dynamic anomalies, challenging traditional theories like mode-coupling.

Contribution

It introduces an extended kinetic constraint model incorporating static attractions, revealing new relaxation mechanisms and non-monotonic relaxation time behaviors.

Findings

Non-monotonic relaxation times with attraction strength

Logarithmic decay of density correlations in time

Crossover from super-Arrhenius to Arrhenius behavior

Abstract

We demonstrate that an extended picture of kinetic constraints in glass-forming liquids is sufficient to explain dynamic anomalies observed in dense suspensions of strongly attracting colloidal particles. We augment a simple model of heterogeneous relaxation with static attractions between facilitating excitations, in a way that mimics the structural effect of short-ranged interparticle attractions. The resulting spatial correlations among facilitated and unfacilitated regions give rise to new relaxation mechanisms that account for non-monotonic dependence of relaxation times on attraction strength as well as logarithmic decay of density correlations in time. These unusual features are a simple consequence of spatial segregation of kinetic constraints, suggesting an alternative physical perspective on attractive colloids than that suggested by mode-coupling theory. Based on the behavior of our model, we predict a crossover from super-Arrhenius to Arrhenius temperature dependence as attractions become dominant at fixed packing fraction.