Issue 5, 2012

Dynamics of charged gibbsite platelets in the isotropic phase

Abstract

We report on depolarized and non-depolarized dynamic light scattering, static light scattering, and steady shear viscosity measurements on interacting charge-stabilized gibbsite platelets suspended in dimethyl sulfoxide (DMSO). The average collective and (long-time) translational self-diffusion coefficients, and the rotational diffusion coefficient, have been measured as functions of the platelet volume fraction ϕ, up to the isotropic–liquid crystal (I/LC) transition. The non-depolarized intensity autocorrelation function, measured at low scattering wavenumbers, consists of a fast and a slowly decaying mode which we interpret as the orientationally averaged collective and translational self-diffusion coefficients, respectively. Both the rotational and the long-time self-diffusion coefficients decrease very strongly, by more than two orders of magnitude, in going from the very dilute limit to the I/LC transition concentration. A similarly strong decrease, with increasing ϕ, is observed for the inverse zero-strain limiting steady shear viscosity. With increasing ϕ, increasingly strong shear-thinning is observed, accompanied by a shrinking of the low shear-rate Newtonian plateau. The measured diffusion coefficients are interpreted theoretically in terms of a simple model of effective charged spheres interacting by a screened Coulomb potential, with hydrodynamic interactions included. The disk-like particle shape, and the measured particle radius and thickness polydispersities, enter into the model calculations via the scattering amplitudes. The interaction-induced enhancement of the collective diffusion coefficient by more than a factor of 20 at larger ϕ is well captured in the effective sphere model, whereas the strong declines of the experimental translational and rotational self-diffusion coefficients are underestimated.

Graphical abstract: Dynamics of charged gibbsite platelets in the isotropic phase

Article information

Article type
Paper
Submitted
13 Sep 2011
Accepted
28 Oct 2011
First published
14 Dec 2011

Soft Matter, 2012,8, 1584-1592

Dynamics of charged gibbsite platelets in the isotropic phase

D. Kleshchanok, M. Heinen, G. Nägele and P. Holmqvist, Soft Matter, 2012, 8, 1584 DOI: 10.1039/C1SM06735D

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