GLASS-TRANSITION IN COLLOIDAL HARDE SPHERES - MEASUREMENT AND MODE-COUPLING-THEORY ANALYSIS OF THE COHERENT INTERMEDIATE SCATTERING FUNCTION

Suspensions of identical particles with hard-sphere-like interactions are studied at concentrations for which the equilibrium state is cryst alline. Dynamic light scattering measurements on these suspensions, in their metastable amorphous states prior to crystallization, identify the kinetic glass transition (GT) by the arrest of particle concentrat ion fluctuations on the experimental time scale. This kinetic glass tr ansition coincides with a spectacular change in the mechanism of cryst allization from the formation of small crystals, which appear homogene ously nucleated throughout the sample at concentrations below the tran sition, to the growth, above the transition, of larger and highly asym metric crystals whose shape and orientation depend on the shear histor y of the suspension. The intermediate scattering functions are measure d over a time window spanning up to eight decades and for several wave vectors near the position of the main structure factor peak. From an analysis of the data in terms of the idealized version of mode-couplin g theory, we conclude that both alpha and beta processes are necessary to describe the slow structural relaxation in the fluid near the GT. The superposition principle of the a process, for the colloidal fluid, and the factorization property of the beta process, for the colloidal fluid and glass, are verified.