Phase diagram, structure and rheology of boehmite dispersions: role of electrostatic interactions

Abstract

Improving industrial processes such as filtration of colloidal suspensions requires an in depth understanding of colloidal stability that is linked to interparticle interactions. One way of investigating such phenomena is to determine colloidal phase diagrams and to characterize structure and rheology in various regions of the phase diagrams. Such a strategy was applied in the present paper to the case of boehmite dispersions. The phase diagram of this material, obtained from osmotic stress experiments shows a non trivial behavior, as the sol/gel transition line of boehmite displays a positive slope at low ionic strength and a negative one at higher ionic strength. Combining structural (SAXS) and rheological measurements, it appears that such a behavior can be linked to the ratio between particle anisotropy and Debye length. Such an interpretation is confirmed by modeling the evolution of elastic moduli in various regions of the phase diagram. The model developed takes into account the anisometric nature of particles and provides reasonably accurate predictions of the electrostatic interaction potential in the system.