Motions in binary mixtures of hard colloidal spheres: melting of the glass.

Dynamic light-scattering experiments are performed on binary mixtures of hard-sphere-like colloidal suspensions with a size ratio of 0.6. The optical properties of the particles are such that the relative contrast of the two species is very sensitive to temperature, a feature that is exploited to obtain the three partial coherent intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or arrest of the alpha process, on the time scale of the experiment. This is observed in a one-component suspension at a packing fraction of 0.575. The intermediate scattering functions measured on the mixtures quantify how, on introduction of the smaller spheres, the alpha process is released, i.e., how the glass melts. Increasing the fraction of smaller particles causes the alpha process to speed up but, at a given wave vector, also incurs a change to its amplitude in proportion to the change in the (partial) structure factor.