Structure and short-time dynamics in suspensions of charged silica spheres in the entire fluid regime

Abstract

We present an experimental study of short-time diffusion properties in fluidlike suspensions of monodisperse charge-stabilized silica spheres suspended in dimethylformamide. The static structure factor S͑q͒, the short-time diffusion function D͑q͒, and the hydrodynamic function H͑q͒ 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 de-ionized 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 accordance 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.

Surface and Interface Analyses of Polymer Brushes by Synchrotron Radiation

“…Taking this advantage, the studies of concentrated colloidal suspensions have been energetically conducted, and the understanding of hydrodynamic interactions of diffusive motion has been developed. [36][37][38][39][40] Though the DLS experiments are conducted with full coherent light source, visible laser, the light source of XPCS is not usually fully coherent. Here, we will consider about the coherence of the X-ray obtained from the third generation synchrotron radiation source, which is a chaotic source with Gaussian intensity distribution.…”

The intensity correlation function in evanescent wave scattering

“…These theories have been verified by experiments on various colloidal systems with different pair-interaction potentials [15,16,17,18].…”

“…(17,18) denote the average with respect to P w eq . The above result (16)(17)(18)) is a generalization of the bulk expressions (2,3) and (5) for the short-time behaviour of g 1 . For very large penetration depths (κ → 0), they reduce to these well-known bulk expressions, as they should.…”

“…In eqs. (17,18), n A/κ is the number of particles within the probed scattering volume, with n the bulk particle number density and A the illuminated area. The brackets < · · · > in eqs.…”

“…Here, lim ∞ denotes the thermodynamic limit, which is also understood to be taken in the definitions in eqs. (17,18) for the hydrodynamic function and wall structure factor, respectively. In order to carry out the thermodynamic limit, lim ∞ , we select the cuboidal shape of the system with volume V = L x L y L z and go with L x , L y and L z uniformly to infinity keeping the bulk density n constant.…”