title: Out-of-equilibrium dynamics of a fractal model gel.
abstract: Using molecular dynamics computer simulations we investigate the dynamics of a gel. We start from a fractal structure generated by the diffusion limited cluster aggregation-deflection 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 zero temperature, we let it evolve at a fixed finite temperature. Depending on the temperature T we find different scenarios for the dynamics. For T approximately > 0.2 the fractal structure is unstable and breaks up into small clusters which relax to equilibrium. For T approximately < 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 chainlike filaments, and heterogeneity.
authors.affiliation: Laboratoire des Colloïdes, Verres et Nanomatériaux, UMR 5587, Université Montpellier 2, F-34095 Montpellier, France.
authors.forename: M-A
authors.initials: MA
authors.lastname: Suarez
authors.forename: N
authors.initials: N
authors.lastname: Kern
authors.forename: E
authors.initials: E
authors.lastname: Pitard
authors.forename: W
authors.initials: W
authors.lastname: Kob