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Issue 5, 2012
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Dynamics of charged gibbsite platelets in the isotropic phase

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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

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Publication details

The article was received on 13 Sep 2011, accepted on 28 Oct 2011 and first published on 14 Dec 2011


Article type: Paper
DOI: 10.1039/C1SM06735D
Citation: Soft Matter, 2012,8, 1584-1592
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    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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