Rheology and microstructure of dense suspensions of plate-shaped colloidal particles

Abstract

The flow properties and microstructure of dense kaolin clay suspensions are explored for vol. fractions, .vphi., as large as 0.39. To avoid flocculation these particles were suspended in pH 10 buffer solns. where edge-face interactions are negligible. These plate-shaped particles have an aspect ratio of 10-12 and, thus, are likely to show alignment above a crit. vol. fraction .vphi.* > 0.10. At low .vphi., the suspensions are Newtonian but show substantial orientation with increased shear rate. As .vphi. is increased, the suspensions develop a yielding type of behavior. In the concd. region .vphi. > .vphi.*, elastic moduli are a function of the previously applied shear rate, γ, decreasing from a low shear rate plateau of G'(0) to a high shear rate plateau of G'(.infin.). We interpret the modulus behavior as being a consequence of changes in alignment of domains in the suspension. Cond. and x-ray scattering measurements confirm that particle alignment increases with increasing shear rate. The normalized modulus value, Gnorm'=[G'(γ)-G'(.infin.)]/[G'(0)-G'(.infin.)], is independent of .vphi. indicating that the characteristic alignment shear rate is independent of vol. fraction. Conductivities and x-ray scattering intensities normalized in the same manner are also independent of the vol. fraction, and superimpose on the modulus data. Surprisingly, these data indicate that fractional particle alignment at a given shear rate is independent of .vphi. for 0.05 < .vphi. < 0.39. [on SciFinder(R)]