Cooperative jump motions in colloidal glass

We report Brownian dynamics simulation results on binary colloidal mixtures of particles of two different diameters interacting via a repulsive DLVO potential. As the effective temperature is lowered by reducing charged impurity concentration, a transition from liquid to crystal at a total volume fraction φ of 0.2 and to glassy state at φ= 0.3 are observed. The mean squared displacements show a marked subdiffusive behavior at intermediate and long times below a certain temperature. The particle motion in supercooled liquid with φ= 0.3 is strongly cooperative as revealed by mean squared displacements, self-part of van-Hove density correlation functions and non-Gaussian parameter. Interestingly, a few particles exhibit cooperative hop and subsequent hop-back motion at temperatures very close to the glass transition