Dynamical heterogeneities in attractive colloids

We study the formation of a colloidal gel by means of molecular dynamics simulations of a model for colloidal suspensions. A slowing down with gel-like features is observed at low temperatures and low volume fractions, due to the formation of persistent structures. We show that at low volume fraction the dynamical susceptibility, which describes dynamical heterogeneities, exhibits a large plateau, dominated by clusters of long living bonds. At higher volume fraction, where the effect of the crowding of the particles starts to be present, it crosses over towards a regime characterized by a peak. We introduce a suitable mean cluster size of clusters of monomers connected by 'persistent' bonds which well describes the dynamical susceptibility. (letter)