Dynamical perspective of the freezing transition of a suspension of hard spheres from the velocity autocorrelation function

The velocity autocorrelation function of concentrated colloidal fluids of hard-sphere particles, measured by dynamic light scattering, decays to the experimental noise floor from below. The decay follows a stretched exponential function of delay time for the colloidal fluid in thermodynamic equilibrium, and a power law for the nonequilibrium, undercooled colloidal fluid. Consideration of this difference between the two states points to a possible dynamical mechanism of freezing.