  We study the rotational diffusion of aging Laponite suspensions for a wide
range of concentrations using depolarized dynamic light scattering. The
measured orientational correlation functions undergo an ergodic to non-ergodic
transition that is characterized by a concentration-dependent
ergodicity-breaking time. We find that the relaxation times associated with
rotational degree of freedom as a function of waiting time, when scaled with
their ergodicity-breaking time, collapse on two distinct master curves. These
master curves are similar to those previously found for the translational
dynamics; The two different classes of behavior were attributed to colloidal
gels and glasses. Therefore, the aging dynamics of rotational degree of freedom
provides another signature of the distinct dynamical behavior of colloidal gels
and glasses.
