On the Refractive Index of Ageing Dispersions of Laponite

TL;DR

This study investigates how the refractive index of Laponite dispersions varies with concentration, temperature, and ageing time, revealing a water-like behavior and a phase transition from isotropic to biphasic states.

Contribution

It provides the first detailed analysis of the refractive index behavior of ageing Laponite dispersions, highlighting their water-like optical properties and phase transition effects.

Findings

Refractive index depends on concentration and temperature, not on ageing time.

Extended Lorenz-Lorentz equation fits the data well.

Refractive index shows a phase transition from isotropic to biphasic states.

Abstract

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.