Abstract
William van Megen: „What happens at freezing? - A perspective from the first order transition in a suspension of hard spheres.”
University of Melbourne, Australia
The auto-correlation function of the longitudinal particle current, C(q,τ), is determined from dynamic light scattering measurements for a suspension of particles with hard sphere-like interactions. For suspensions in thermodynamic equilibrium we find scaling of the space and time variables of C(q,τ). Thus, a separation into fast fluctuations, delta correlated in time, and slow overdamped longitudinal modes, independent of the spatial scale, is exposed. Moreover, this finding supports the notion that the movement of suspended particles can be described in terms of uncorrelated Brownian encounters. The time scale of the slow mode decreases with increasing volume fraction. At the freezing value (=0.493) a conflict is struck in that the Brownian fluctuations and the overdamped longitudinal modes are both delta-correlated in time. Deviation from scaling suggest the existence of a structural memory in the metastable suspension (ie, at volume fractions above freezing value) not present in the thermodynamically stable case.