Passive Microrheology for Measurement of the Concentrated Dispersions Stability

Abstract

This work presents a new technique of passive microrheology for the study of the microstructural properties of soft materials such as emulsions or suspensions. This technology uses Multi Speckle Diffusing Wave Spectroscopy (MS-DWS) set-up in a backscattering configuration with video camera detection. It measures the mean displacement of the microstructure particles in a spatial range between 0.1 and 100 nm and a time scale between 10⁻² and 10⁵ s. Different parameters can be measured or obtained directly from the Mean Square Displacement (MSD) curve, including a fluidity index, a solid–liquid balance, an elasticity index, a viscosity index, a relaxation time and a MSD slope.

Using this technique the evolution of the microstructure, the restructuring after shearing and the variation of the viscoelastic properties with temperature or pH can be measured allowing the physical stability of emulsions or suspensions to be forecasted.

This work focuses on the evolution of the viscoelastic properties of emulsions and suspensions to follow their stability over time and shows the advantages of using a non-invasive method to detect nascent destabilisation of the microstructure.