exchangeable and in aqueous dispersions these ions diffuse The rheological properties of aqueous dispersions of the syninto the water and plate-like particles with negatively thetic hectorite clay Laponite RD that form gel-like structures charged faces are formed. The charge on the oxide edge of have been investigated. Special emphasis has been laid on the the platelets is less negative or even positive depending upon phenomenon of thixotropy. Structural recovery at rest after steady the pH of the dispersing medium. The average size of these shear is considered a fundamental thixotropic process and has particles is 30 nm in diameter and 1-4 nm in height, as been characterized by small amplitude oscillatory shear measurerevealed by electron microscopy (5, 6) and independently ments. A special sealing technique was used to prevent the evapoconfirmed by various scattering techniques (6-8) and ultraration of water during these experiments. After cessation of steady centrifuge analysis (8). Thus these particles are an order of shear รh*ร increases monotonically with time and even after 16 days no equilibrium viscosity value is reached. A single power law magnitude smaller than those in refined natural clays.
รh*ร ร t n holds within the time regime from 10 to 10 6 s. The Generally, two different mechanisms for gelation in clay exponent n ร
0.13 { 0.02 is independent of clay concentration mineral dispersions are proposed, leading to different types and mechanical pre-treatment of the material. This type of kinetics of three-dimensional ordering. In the first case the formation has not been reported so far for the thixotropic recovery of any of an equilibrium structure is induced by long-range electroclay dispersion and it does not fit the common definition of thixotstatic repulsion between interacting double-layers. This ropy. The reorganization of the gel structure determining this mechanism, which has been proposed by Norrish (9) and thixotropic phenomenon is interpreted as a cooperative self desupported by experiments of Callaghan and Ottewill (10), laying process similar to the aging of glassy polymers or precipitaaccounts for gel formation at low electrolyte concentration tion from supersaturated solid solutions.