The cage effect is generally invoked when discussing the delay in the decay of time correlation functions of dense fluids. In an attempt to examine the role of caging more closely, we consider the spread of the displacement distributions of Brownian particles. These distributions are necessarily biased by the presence of neighbouring particles. Accommodation of this bias by those neighbours conserves the displacement distribution locally and presents a collective mechanism for exploring configuration space that is more efficient than the intrinsic Brownian motion. Caging of some particles incurs, through the impost of global conservation of the displacement distribution, a delayed, non-local collective process. This non-locality compromises the efficiency with which configuration space is explored. Both collective mechanisms incur delay or stretching of time correlation functions, in particular the particle number and flux densities. This paper identifies and distinguishes these mechanisms in existing data from experiments and computer simulations on systems of particles with hard sphere interactions.
Radial distribution functions and structure factors are calculated for dilute, but strongly interacting electrostatically stabilized dispersions of small spherical particles. The calculations, based on the usual screened coulomb interaction between the particles, examine the sensitivity of the structure of these colloidal solutions to the background electrolyte concentration, temperature and the particle surface charge.
Mean squared displacements and velocity auto correlation functions are calculated using molecular dynamics for hard spheres under a range of conditions (i) for the equilibrium fluid below freezing; (ii) for the metastable fluid above freezing; and (iii) for the hard sphere crystal, both in the metastable region between freezing and melting, and in the stable region above melting. In addition, simulations are carried out for a metastable Lennard-Jones system. The results confirm recent studies that indicated the disappearance of the classical Alder long-time tail, and show that they apply to systems other than the metastable hard sphere fluid. The implications of these results for our understanding of crystallization and the glass transition are discussed.
Dynamic light scattering measurements are reported for suspensions at concentrations around the glass transition. Self intermediate scattering functions are obtained by employing a mixture of identically interacting but optically contrasting polymer and silica particles and adjusting the refractive index of the suspending liquid until scattering from the structure is eliminated. A small spread in particle radii retards nucleation and crystal growth to an extent that allows characterization of (density) quenched metastable fluid states. The non-equilibrium nature of the glass state in evidenced by the dependence of the intermediate scattering functions on the waiting time.
Various aspects of the behaviour of essentially hard spherical colloidal particles, suspended in a liquid, are outlined. The authors consider the phase behaviour and crystal structure of one- and two-component suspensions and the glass transition of a one-component system.
The grand canonical ensemble Monte Carlo method is applied to monovalent and divalent symmetric primitive model electrolytes between plane charged surfaces. Results for continuous and discrete surface charge distributions are compared with the Gouy–Chapman theory.
We present the results of crystallographic measurements on samples of two latexes: one with a relatively symmetric particle size distribution, and another with a highly skewed pseudobimodal distribution. For the skewed latex, crystallites are clearly visible, but they exhibit only a single Bragg reflection, indicating long-range order in only one direction. We propose a schematic model that explains this result in terms of stacks of planes, which are unregistered due to a high incidence of stacking faults caused by the incorporation of a large number of small particles.
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