Predicting the Stability of Dispersions with a Yield Stress
Application Note Apr 28, 2015
Malvern Instruments Limited
Assessing the long-term stability of a dispersion or emulsion can be both a tedious and time-consuming process; however, it is essential to ensure a product meets quality standards. Formulators often achieve stability through a combination of effects; minimizing interfacial tension, increasing steric or electrostatic repulsion of the dispersed phase and/or by increasing the viscosity of the continuous phase. For dilute dispersions the combined effect of these factors can often be reflected in the zero shear viscosity, which can give an indication of the rate of at which droplets will coalesce and separate, or dispersions will settle. For systems that are more concentrated, formation of a network structure through dispersed phase interaction or particle/droplet jamming may occur. In this case, stability will be largely related to the strength of the network structure, which can be quantified by the yield stress.