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.Comment: 30 pages, 25 figure