Glass transition in colloidal hard spheres: Measurement and mode-coupling-theory analysis of the coherent intermediate scattering function

Abstract

Suspensions of identical particles with hard-sphere-like interactions are studied at concentrations for which the equilibrium state is crystalline. 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 concentration fluctuations on the experimental time scale. This kinetic glass transition coincides with a spectacular change in the mechanism of crystallization from the formation of small crystals, which appear homogeneously nucleated throughout the sample at concentrations below the transition, to the growth, above the transition, of larger and highly asymmetric crystals whose shape and orientation depend on the shear history of the suspension. The intermediate scattering functions are measured 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-coupling theory, we conclude that both α and β processes are necessary to describe the slow structural relaxation in the fluid near the GT. The superposition principle of the α process, for the colloidal fluid, and the factorization property of the β process, for the colloidal fluid and glass, are verified.