Sol–gel transition of colloidal suspensions of anisotropic particles of laponite
The thermodynamical properties, structure and rheology of laponite dispersions have been studied as a function of solid fraction and ionic strength. The dispersions undergo a transition from Newtonian liquid to viscoelastic solid without phase separation. The increase of the ionic strength shifts the transition to lower solid fraction and a phase diagram has been constructed for the onset of viscoelastic solid like behaviour. This sol–gel transition line coincides with the appearance of a singularity in the equation of state as determined by osmotic pressure measurements. Analysis of the dispersions by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) shows correlated but well separated particles. In order to elucidate the nature of the observed sol–gel transition and the particle organization, we discuss the role of particle anisotropy coupled with diffuse-layer repulsion.