Ageing dynamics in Laponite dispersions at various salt concentrations

The ageing dynamics of a charged colloidal system, Laponite suspended in water, have been investigated by photon correlation technique. The samples covered a novel and very wide range of clay concentrations (C-w = 0.3-3.1 wt%) and four different NaCl concentrations (Cs = 1 x 10(-4) M, 1 x 10(-3) M, 2 x 10(-3) M and 5 x 10(-3) M) and were studied to investigate the phase diagram, which has been a subject of discussion in recent literature. A clear picture of the Laponite phase diagram has been obtained. The measurements show the existence of two different dynamical routes to reach a final arrested state and the presence of a transition line between them in the C-w-C-s plane.