Résumé
By means of molecular dynamics simulations, we study the structure and the dynamics of a microscopic model for colloidal gels at low volume fractions. The presence of directional interactions leads to the formation of a persistent interconnected network at temperatures where phase separation does not occur. We find that large scale spatial correlations strongly depend on the volume fraction and characterize the formation of the persistent network. We observe a pre-peak in the static structure factor and relate it to the network structure. The slow dynamics at gelation is characterized by the coexistence of fast collective motion of the mobile parts of the network structure (chains) with large scale rearrangements producing stretched exponential relaxations. We show that, once the network is sufficiently persistent, it induces slow, cooperative processes related to the network nodes. We suggest that this peculiar glassy dynamics is a hallmark of the physics of colloidal gels at low volume fractions.