Effects of aging on the yielding behaviour of acid and salt induced Laponite gels

Abstract

The synthetic clay Laponite, when dispersed in water, shows rich phase behaviour that depends on both clay and ionic concentrations. The flow properties of this clay dispersion can be tuned by incorporating different additives such as acid and salt. In this work, we use rheology to study the mechanical properties of Laponite gels when prepared by adding sulfuric acid (H2SO4) and common salt (NaCl). The acid induced Laponite gels form a visco-elastic solid with increasing idle time, while the salt induced Laponite gel transforms to a soft solid almost immediately after sample preparation. Furthermore, in the acid induced Laponite gels, a nonmonotonic evolution of yield stress with idle time is observed. No such observation is evident for the salt induced Laponite gels. These observations are connected to the underlying morphology of the sample which is governed by the osmotic pressure driven aging behaviour of the suspensions. We use cryogenic scanning electron microscopy images for a qualitative understanding of the gel morphologies which we relate to the acquired rheological data. The aging dynamics and the subsequent structural evolution of the sample are further verified by performing a UV–Vis spectroscopy study and found to be in agreement with the rheological and Cryo-SEM experiments.