SOL-GEL TRANSITION OF COLLOIDAL SUSPENSIONS OF ANISOTROPIC PARTICLES OF LAPONITE

The thermodynamical properties, structure and rheology of laponite dis persions have been studied as a function of solid fraction and ionic s trength. The dispersions undergo a transition from Newtonian liquid to viscoelastic solid without phase separation. The increase of the ioni c strength shifts the transition to lower solid fraction and a phase d iagram has been constructed for the onset of viscoelastic solid like b ehaviour. This sol-gel transition line coincides with the appearance o f a singularity in the equation of state as determined by osmotic pres sure measurements. Analysis of the dispersions by transmission electro n microscopy (TEM) and small-angle X-ray scattering (SAXS) shows corre lated but well separated particles. In order to elucidate the nature o f the observed sol-gel transition and the particle organization, we di scuss the role of particle anisotropy coupled with diffuse-layer repul sion.