Chemical Stability of Laponite in Aqueous Media

TL;DR

This study investigates the stability of Laponite in aqueous dispersions, revealing that pH does not influence dissolution and that sodium ions from Laponite may prevent its dissolution, challenging previous assumptions.

Contribution

It demonstrates that Laponite's dissolution is unaffected by pH and highlights the role of sodium ions in stabilizing Laponite, providing new insights into its stability mechanisms.

Findings

pH has no effect on Laponite dissolution within pH 3-10.

Dissolution occurs even at pH above 10 for low concentrations.

Higher concentration dispersions show no dissolution, linked to sodium ion concentration.

Abstract

In this work stability of Laponite against dissolution in its aqueous dispersions is investigated as a function of initial pH of water before mixing Laponite, and concentration of Laponite. Dissolution of Laponite is quantified in terms of concentration of leached magnesium in the dispersions. Interestingly the solvent pH is observed to play no role in dissolution of Laponite in dispersion over the explored range of 3 to 10. Furthermore, contrary to the usual belief that Laponite dissolves when pH of aqueous dispersion decreases below 9, dissolution of the same is observed even though dispersion pH is above 10 for low concentrations of Laponite (1 and 1.7 mass%). On the other hand, for dispersions having high concentration of Laponite (2.8 mass%) and pH in the similar range (>10) no dissolution is observed. Measurement of ionic conductivity of dispersion shows that concentration of sodium ions in dispersion increases with concentration of Laponite, which appears to have a role in preventing the dissolution of Laponite.