In:
The Journal of Chemical Physics, AIP Publishing, Vol. 137, No. 11 ( 2012-09-21)
Abstract:
We report a comprehensive joint experimental-theoretical study of the equilibrium pair-structure and short-time diffusion in aqueous suspensions of highly charged poly-acrylate (PA) spheres in the colloidal fluid phase. Low-polydispersity PA sphere systems with two different hard-core radii, R0 = 542 and 1117 Å, are explored over a wide range of concentrations and salinities using static and dynamic light scattering (DLS), small angle x-ray scattering, and x-ray photon correlation spectroscopy (XPCS). The measured static and dynamic scattering functions are analyzed using state-of-the-art theoretical methods. For all samples, the measured static structure factor, S(Q), is in good agreement with results by an analytical integral equation method for particles interacting by a repulsive screened Coulomb plus hard-core pair potential. In our DLS and XPCS measurements, we have determined the short-time diffusion function D(Q) = D0 H(Q)/S(Q), comprising the free diffusion coefficient D0 and the hydrodynamic function H(Q). The latter is calculated analytically using a self-part corrected version of the δγ-scheme by Beenakker and Mazur which accounts approximately for many-body hydrodynamic interactions (HIs). Except for low-salinity systems at the highest investigated volume fraction ϕ ≈ 0.32, the theoretical predictions for H(Q) are in excellent agreement with the experimental data. In particular, the increase in the collective diffusion coefficient Dc = D(Q → 0), and the decrease of the self-diffusion coefficient, Ds = D(Q → ∞), with increasing ϕ is well described. In accord with the theoretical prediction, the peak value, H(Qm), of H(Q) relates to the nearest neighbor cage size ∼2π/Qm, for which concentration scaling relations are discussed. The peak values H(Qm) are globally bound from below by the corresponding neutral hard-spheres peak values, and from above by the limiting peak values for low-salinity charge-stabilized systems. HIs usually slow short-time diffusion on colloidal length scales, except for the cage diffusion coefficient, Dcge = D(Qm), in dilute low-salinity systems where a speed up of the system dynamics and corresponding peak values of H(Qm) & gt; 1 are observed experimentally and theoretically.
Type of Medium:
Online Resource
ISSN:
0021-9606
,
1089-7690
Language:
English
Publisher:
AIP Publishing
Publication Date:
2012
detail.hit.zdb_id:
3113-6
detail.hit.zdb_id:
1473050-9
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