Dynamical Heterogeneities in the Crossover Region from Gel-like to Glassy-like Behavior

We study the dynamical heterogeneities along the attractive glass line in a model for charged colloids, where short-range attraction competes with long-range repulsion. We focus on the crossover from gel-like to glassy-like regime, where the system displays both features of chemical gels and of glassy systems. The former are due to long living clusters the latter to crowding effects, which both slow down the relaxation process. We show how to separate the two effects by looking at the fluctuation of the self Intermediate Scattering Function, chi (4)(k,t), for different values of wave vector k. For small values of k, chi (4)(k,t) detects the dynamical behavior at large length scale, where both cluster effects and crowding effects are present. On the other hand by increasing the value of k, chi (4)(k,t) detects the dynamical behavior at small length scale where the cluster effects are suppressed and only the crowding effects dominate the dynamics.