Structure and Short-time Dynamics in Suspensions of Charged Silica Spheres in the entire Fluid Regime

TL;DR

This study investigates the short-time diffusion and structure of charged silica sphere suspensions in a fluid, demonstrating consistency with theoretical models and simulations across various conditions, including near phase boundaries.

Contribution

It provides comprehensive experimental data on short-time dynamics in charged colloidal suspensions and validates the renormalized density fluctuation expansion theory across a wide parameter range.

Findings

Dynamic properties decrease with increasing salt content.

Experimental results agree with theoretical predictions and simulations.

Hydrodynamic function peak height is bounded by freezing criteria.

Abstract

We present an experimental study of short-time diffusion properties in fluid-like suspensions of monodisperse charge-stabilized silica spheres suspended in DMF. The static structure factor S(q), the short-time diffusion function, D(q), and the hydrodynamic function, H(q), in these systems have been probed by combining X-ray photon correlation spectroscopy experiments with static small-angle X-ray scattering. Our experiments cover the full liquid-state part of the phase diagram, including deionized systems right at the liquid-solid phase boundary. We show that the dynamic data can be consistently described by the renormalized density fluctuation expansion theory of Beenakker and Mazur over a wide range of concentrations and ionic strengths. In accord with this theory and Stokesian dynamics computer simulations, the measured short-time properties cross over monotonically, with increasing salt content, from the bounding values of salt-free suspensions to those of neutral hard spheres. Moreover, we discuss an upper bound for the hydrodynamic function peak height of fluid systems based on the Hansen-Verlet freezing criterion.