DYNAMIC-LIGHT-SCATTERING STUDY OF GLASSES OF HARD COLLOIDAL SPHERES

Dynamic light scattering is applied to the glass phase of nonaqueous suspensions of sterically stabilized colloidal spheres. The short-ranged steric repulsion ensures that the particle interactions are close to hard sphere. This is supported by the observation that the equilibrium phase behavior of these suspensions agrees with that predicted for the hard-sphere atomic system. We verify a model for a nonergodic medium, which assumes that the particles are localized during an experiment and which allows the intermediate scattering function to be calculated from a single measurement of the time-averaged intensity autocorrelation function. Intermediate scattering functions are obtained for several concentrations over a range of wave vectors around the main diffraction peak. The measured nonergodicity parameters are in good agreement with the predictions of mode-coupling theory for the hard-sphere glass. The comparison involves no adjustable parameters. At long times the intermediate scattering functions can be scaled to a single curve for over 2.5 decades in time. This, combined with the results that the nonergodicity parameters and critical amplitudes required for the scaling are in quantitative agreement with mode-coupling theory, provides a convincing verification of the predicted factorization property of the beta process in the glass phase.