The dynamical fragile-to-strong crossover in attractive colloidal systems

The dynamics of a hierarchical colloid solution, dendrimer in methanol, has been studied using photon-correlation spectroscopy (PCS). The obtained relaxation curves are analyzed according to the mode-coupling theory (MCT). The main results are: i) the occurrence of a fragile to strong dynamical crossover as a function of the packing fraction at ϕc ≃ 0.39, and ii) the observation of a secondary relaxation (β) that has its onset just at the dynamical crossover and is correlated with the primary α-relaxation. Finally we discuss the obtained findings in comparison with recent experiments in similar systems characterized by an attractive interaction obtaining a confirmation on the primary role of the dynamical crossover in the physics of the dynamical arrest.