Aging Dynamics of a Fractal Model Gel

TL;DR

This study uses molecular dynamics simulations to explore how a fractal gel structure ages under different temperatures, revealing stability, structural breakdown, and anomalous dynamics depending on thermal conditions.

Contribution

It introduces a detailed simulation of aging in a fractal gel with combined short-range attraction and long-range repulsion, highlighting temperature-dependent stability and dynamics.

Findings

High T (>0.2) leads to structural breakup and relaxation.

Low T (<0.2) results in stable structures with slowed dynamics.

Anomalous t^{2/3} mean squared displacement observed.

Abstract

Using molecular dynamics computer simulations we investigate the aging dynamics of a gel. We start from a fractal structure generated by the DLCA-DEF algorithm, onto which we then impose an interaction potential consisting of a short-range attraction as well as a long-range repulsion. After relaxing the system at T=0, we let it evolve at a fixed finite temperature. Depending on the temperature T we find different scenarios for the aging behavior. For T>0.2 the fractal structure is unstable and breaks up into small clusters which relax to equilibrium. For T<0.2 the structure is stable and the dynamics slows down with increasing waiting time. At intermediate and low T the mean squared displacement scales as t^{2/3} and we discuss several mechanisms for this anomalous time dependence. For intermediate T, the self-intermediate scattering function is given by a compressed exponential at small wave-vectors and by a stretched exponential at large wave-vectors. In contrast, for low T it is a stretched exponential for all wave-vectors. This behavior can be traced back to a subtle interplay between elastic rearrangements, fluctuations of chain-like filaments, and heterogeneity.