Interdiffusion in Colloidal Mixtures
G. Nägele in collaboration with A.J. Banchio (National University of Cordoba, Argentina) and H. Zhang (Shanghai Jiao Tong University, P.R. of China)
Colloidal mixtures are abundant in many industrially synthesized and naturally occurring (non-biological) colloidal fluids. Mixing effects in colloidal mixtures are intriguing since the mixing of differently sized and interacting particles strongly influences the diffusion and rheological behavior of the suspension. In mixtures, additional diffusion mechanisms not present in monodisperse suspensions do occur, such as interdiffusion and tracer-diffusion.
Fig. 1 Interdiffusion coefficient Din and kinetic coefficient Λin of a binary hard-sphere mixture of total volume fraction φ = 0.1 and radius ratio λ =a1/a2 =1/3, versus composition fraction, y1
= φ1/φ, of component 1. Both Din and Λin are normalized by the free diffusion coefficient D10
of component 1. Also shown are the long-time tracer-diffusion coefficients DL1 and DL2, normalized by D10
. From [1].
The relaxation of thermal fluctuations in the composition of two components in a many-component colloidal mixture is referred to as the interdiffusion process. In a recent study we have analyzed the interdiffusion process in mixtures of spherical particles [1]. Exact analytic expressions have been derived for the interdiffusion coefficient of a semi-dilute mixture of colloidal hard spheres, in terms of the component volume fractions, φi, and the particle size ratio λ. These expressions can be used for analyzing dynamic scattering data from mixtures. Our exact results have been compared to corresponding mode-coupling theory (MCT) calculations, revealing the shortcomings of the MCT at low concentrations. The near-field part of the hydrodynamic interactions is shown to be essential. We have studied whether the interdiffusion coefficient is expressible in terms of the component self-diffusion coefficients.
In ongoing work, we address interdiffusion in charge-stabilized colloidal mixtures, in mixtures of weakly attractive particles, and in electrolyte mixtures [2].
References:
[1] G. Nägele, H. Zhang, C. Contreras-Aburto and A.J. Banchio, paper in preparation (2014).
[2] G. Nägele, The Physics of Colloidal Soft Matter, Lecture Notes 14, Polish Academy of Sciences Publishing, Warsaw (2004). ISSN 1642-0578.
