Collective modes in hard sphere systems; cage effect

by William van Megen (Royal Melbourne Institute of Technology, Melbourne, Australia)

Thursday 27 Apr 2017, 15:00 → 17:00 Europe/Rome

Aula 4 (Dipartimento di Fisica - Ed. E.Fermi)

The slowing of diffusion and delay of the structural relaxation of a fluid when its density is increased is considered a manifestation of the so-called “cage effect”: the microscopic picture in which particles are trapped by their respective neighbours. An attempt to examine the role of caging more closely considers the spread of the displacement distributions of Brownian particles. These distributions are necessarily biased by the presence of neighbouring particles. Accommodation of this bias conserves the displacement distribution locally and presents a collective mechanism for exploring configuration space that turns out to be more efficient than the intrinsic Brownian motion. Blocking of the bias affects caging of some particles, through the impost of global conservation of probability (the average number of caged particles), a delayed, non-local collective process. This presentation identifies and distinguishes these mechanisms in dynamic light scattering experiments and computer simulations of hard sphere particles.