Dynamic light-scattering measurements are reported for suspensions at concentrations in the vicinity of the glass transition. In a mixture of identically sized but optically different particles having hard-sphere-like interactions, we project out the incoherent ͑or self-͒ intermediate scattering functions by adjusting the refractive index of the suspending liquid until scattering from the structure is suppressed. Due to polydispersity, crystallization is sufficiently slow so that good estimates of ensemble-averaged quantities can be measured for the metastable fluid states. Crystallization of the suspensions is still exploited, however, to set the volume fraction scale in terms of effective hard spheres and to eliminate ͑coherent͒ scattering from the structure. The glasstransition volume fraction is identified by the value where large-scale particle motion ceases. The nonequilibrium nature of the glass state is evidenced by the dependence on the waiting time of the long time decay of the relaxation functions. The self-intermediate scattering functions show negligible deviation from Gaussian behavior up to the onset of large-scale diffusion in the fluid or the onset of waiting time effects in the glass.

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Self-intermediate scattering functions (ISFs) are measured by dynamic light scattering for the colloidal fluid of hard spheres for both equilibrium and nonequilibrium (undercooled) conditions, i.e., for volume fractions below and above the known freezing transition of the hard-sphere system. The delay time tau(m) where the mean-squared displacement, or the low wave-vector limit of the ISF, exhibits its maximum stretching is identified as a characteristic of the non-Markovian process(es) and is used to separate the ISF into fast (tau < tau(m)) and slow (tau > tau(m)) contributions. Each of these contributions exposes qualitative differences in the dynamics of the particles between the equilibrium and nonequilibrium colloidal fluids. These changes in the relaxation scenario signal the colloidal fluid's awareness of its traversal of the freezing volume fraction.

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