AQUEOUS DISPERSIONS OF COLLOIDAL GIBBSITE PLATELETS - SYNTHESIS, CHARACTERIZATION AND INTRINSIC-VISCOSITY MEASUREMENTS

We report preparation and properties of model platelets for the study of rheology and structure formation. The colloids are well-defined: re gularly shaped and fairly monodisperse hexagons with an average diamet er of 160 nm and a thickness of 13 nm. Various characterisation techni ques demonstrate that the particles consist of gibbsite. The isoelectr ic point of the edges (pH approximate to 7) differs from that on the f aces (pH approximate to 10). At pH <4, addition of lithium chloride in duces face-to-face aggregation, which causes settling to dense sedimen ts. In the range 7<pH<10, low density gels are formed, probably due to the formation of a fractal network of edge-tc-face aggregates. For st able gibbsite dispersion, low-shear viscosity measurements yield the i ntrinsic viscosity [eta] = 23 and the Huggins coefficient k(H) = 0.4. (C) 1998 Elsevier Science B.V.