Dynamics of charged gibbsite platelets in the isotropic phase

Kleshchanok, D.; Nägele, G.; Holmqvist, P.; Heinen, M.

doi:10.1039/c1sm06735d

Journal Article

PreJuSER-19670

Dynamics of charged gibbsite platelets in the isotropic phase

Kleshchanok, D. ; Heinen, M.FZJ* ; Nägele, G.FZJ* ; Holmqvist, P.FZJ*

2012
Royal Society of Chemistry (RSC) Cambridge

Soft matter 8, 1584 - 1592 (2012) [10.1039/c1sm06735d]

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Please use a persistent id in citations: http://hdl.handle.net/2128/4627 doi:10.1039/c1sm06735d

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 phi, 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 phi, is observed for the inverse zero-strain limiting steady shear viscosity. With increasing phi, 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 phi is well captured in the effective sphere model, whereas the strong declines of the experimental translational and rotational self-diffusion coefficients are underestimated.

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Note: P. Davidson and H.H. Wensink are thanked for enlightening discussions. The work of D.K. was financed by the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organization for Scientific Research (NWO). M.H. acknowledges support by the International Helmholtz Research School of Biophysics and Soft Matter (IHRS BioSoft). G.N. acknowledges funding from the Deutsche Forschungsgemeinschaft (SFB-TR6, project B2).

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