  We report on depolarized and non-depolarized dynamic light scattering, static
light scattering, and static viscosity measurements on interacting charged
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 static 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
volume fractions is well captured in the effective sphere model, whereas the
strong declines both of the experimental translational and rotational
self-diffusion coefficients are underestimated.
