  Colloidal gel aging is investigated using very long runs of brownian dynamics
simulations. The Asakura Oosawa description of the depletion interaction is
used to model a simple colloid polymer mixture. Several regimes are identified
during gel formation. The Intermediate scattering function displays a double
decay characteristic of systems where some kinetic processes are frozen. The
$\beta$ relaxation at short times is explained in terms of the Krall-Weitz
model for the decorelation due to the elastic modes present. The $\alpha$
relaxation at long times is well described by a stretched exponential, showing
a wide spectrum of relaxation times for which the $q$ dependence is
$\tau_{\alpha} = q^{-2.2}$, lower than for diffusion. For the shortest waiting
times, a combination of two stretched exponentials is used, suggesting a
bimodal distribution. The extracted relaxation times vary with waiting time as
$\tau_{\alpha}=\tau_w^{0.66}$, slower than the simple aging case. The real
space displacements are found to be strongly non-Gaussian, correlated in space
and time. We were unable to find clear evidence that the gel aging was driven
by internal stresses. Rather, we hypothesise that in this case of weakly
interacting gels, the aging behaviour arises due to the thermal diffusion of
strands, constrained by the percolating network which ruptures discontinuously.
Although the mechanisms differ, the similarity of some of the results with the
aging of glasses is striking.
