Ageing dynamics in Laponite dispersions at various salt concentrations

Abstract

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 (C _s = 1 × 10⁻⁴ M, 1 × 10⁻³ M, 2 × 10⁻³ M and 5 × 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.