Static and dynamic heterogeneities in irreversible gels and colloidal gelation

TL;DR

This paper investigates the dynamical heterogeneities in gels and glasses, revealing how non-linear susceptibility behavior varies with the permanence of clusters and the system's state, using molecular dynamics simulations.

Contribution

It demonstrates the different behaviors of non-linear dynamical susceptibility in irreversible gels, colloidal gels, and glasses, highlighting the effects of cluster permanence and system parameters.

Findings

In irreversible gels, susceptibility increases with time and approaches mean cluster size.

In glasses, susceptibility peaks and then decreases, indicating transient heterogeneities.

Colloidal gels show a crossover from gel-like to glass-like behavior as volume fraction increases.

Abstract

We compare the slow dynamics of irreversible gels, colloidal gels, glasses and spin glasses by analyzing the behavior of the so called non-linear dynamical susceptibility, a quantity usually introduced to quantitatively characterize the dynamical heterogeneities. In glasses this quantity typically grows with the time, reaches a maximum and then decreases at large time, due to the transient nature of dynamical heterogeneities and to the absence of a diverging static correlation length. We have recently shown that in irreversible gels the dynamical susceptibility is instead an increasing function of the time, as in the case of spin glasses, and tends asymptotically to the mean cluster size. On the basis of molecular dynamics simulations, we here show that in colloidal gelation where clusters are not permanent, at very low temperature and volume fractions, i.e. when the lifetime of the bonds is much larger than the structural relaxation time, the non-linear susceptibility has a behavior similar to the one of the irreversible gel, followed, at higher volume fractions, by a crossover towards the behavior of glass forming liquids.