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

Dynamic light scattering is applied to the glass phase of nonaqueous s uspensions of sterically stabilized colloidal spheres. The short-range d steric repulsion ensures that the particle interactions are close to hard sphere. This is supported by the observation that the equilibriu m phase behavior of these suspensions agrees with that predicted for t he hard-sphere atomic system. We verify a model for a nonergodic mediu m, which assumes that the particles are localized during an experiment and which allows the intermediate scattering function to be calculate d from a single measurement of the time-averaged intensity autocorrela tion function. Intermediate scattering functions are obtained for seve ral concentrations over a range of wave vectors around the main diffra ction peak. The measured nonergodicity parameters are in good agreemen t with the predictions of mode-coupling theory for the hard-sphere gla ss. The comparison involves no adjustable parameters. At long times th e intermediate scattering functions can be scaled to a single curve fo r over 2.5 decades in time. This, combined with the results that the n onergodicity parameters and critical amplitudes required for the scali ng are in quantitative agreement with mode-coupling theory, provides a convincing verification of the predicted factorization property of th e beta process in the glass phase.