Length scale dependence of the dynamical heterogeneities in colloidal gelation at low volume fraction

Using MD simulations of a DLVO interaction potential, we present a systematic study of the slow dynamics in a colloidal suspension undergoing gelation. In particular we consider the dynamical susceptibility, defined as the fluctuation of the self-intermediate scattering function, as a measure of the dynamical heterogeneities. The present study allows us to rationalize the strikingly different behaviors observed at low and high volume fractions, exemplified, in particular, by the strong wavevector dependence of the dynamical heterogeneities in the dilute incipient gel. We provide a rationale for the complex dynamics and the heterogeneities observed on approaching gelation in terms of the aggregation process taking place in the system. The emerging scenario suggests that the strong length scale dependence of the dynamical susceptibility can be taken as the distinctive sign of colloidal gelation at low volume fractions, with respect to the attractive and repulsive glass found at higher densities.