  Aqueous dispersion of Laponite at low ionic concentration is of interest
since it undergoes structural evolution with respect to time, which is usually
termed as ageing. In this work we study the refractive index behavior as a
function of ageing time, concentration and temperature. We observed that the
extended Lorenz-Lorentz equation fitted the refractive index dependence on
concentration and temperature very well. The refractive index did not show any
dependence on ageing time. However, the dependence of refractive index on
concentration showed a marked change as the system underwent transition from an
isotropic to a biphasic state. The slope of the refractive index-density data
is remarkably close to that of water at all Laponite concentrations. In the
context of transport phenomena, optical measurements such as interferometry can
exploit the water-like behavior of Laponite dispersions.
