Bond formation and slow heterogeneous dynamics in adhesive spheres with long--ranged repulsion: Quantitative test of Mode Coupling Theory

TL;DR

This study combines simulations and mode coupling theory to analyze how bond formation leads to slow dynamics and vitrification in colloidal spheres with long-range repulsion, highlighting the role of local bonding over large-scale heterogeneities.

Contribution

It provides a quantitative test of Mode Coupling Theory on a colloidal system with long-range repulsion, linking microscopic bond formation to macroscopic slow dynamics.

Findings

Mode coupling theory semi-quantitatively matches local density correlators.

Bond formation causes arrest, largely unaffected by heterogeneities.

Theory overestimates the lifetime of mesoscopic voids.

Abstract

A colloidal system of spheres interacting with both a deep and narrow attractive potential and a shallow long-ranged barrier exhibits a prepeak in the static structure factor. This peak can be related to an additional mesoscopic length scale of clusters and/or voids in the system. Simulation studies of this system have revealed that it vitrifies upon increasing the attraction into a gel-like solid at intermediate densities. The dynamics at the mesoscopic length scale corresponding to the prepeak represents the slowest mode in the system. Using mode coupling theory with all input directly taken from simulations, we reveal the mechanism for glassy arrest in the system at 40% packing fraction. The effects of the low-q peak and of polydispersity are considered in detail. We demonstrate that the local formation of physical bonds is the process whose slowing down causes arrest. It remains largely unaffected by the large-scale heterogeneities, and sets the clock for the slow cluster mode. Results from mode-coupling theory without adjustable parameters agree semi-quantitatively with the local density correlators but overestimate the lifetime of the mesoscopic structure (voids).