Emulsion Stability Analysis Using Optical Scanning for Predicting Shelf-Life of Formulations

Emulsions are unstable colloidal systems that undergo many destabilization phenomena (coalescence, flocculation, creaming, etc.) resulting from various causes (i.e. lack of surfactant to cover the interface, attractive forces, etc.). Therefore, it is very important for the formulator to know the nature of these processes to be able to overcome them, resulting in a more stable product. For many reasons (coexistence of large and small droplets, chemical interactions, etc.) droplets tend to flocculate. The addition of surfactants may minimize these problems.   Using an optical scanning instrument, it is possible to investigate how different surfactants influence the flocculation of droplets, as well as the effect of surfactant concentration and also storage temperature.    Instruments using optical scanning methods for stability analysis of emulsions, dispersions, and foams have been available for the past 25 years but before today, were not capable of true particle size analysis since they generally operated with a only a single-wavelength light source. This paper will introduce a new optical scanning capability whereby the same sample can be tested with 2 different wavelengths of light, both near-infrared and near-ultraviolet. This is a significant development because comparing measurements made on the same sample at two distinctly separate wavelengths of light will be shown to give higher sensitivity to smaller particles. It therefore gives the opportunity to yield more accurate particle size distribution, a capability long-desired by the cosmetics and personal care products industries. In addition, 'freeze & thaw' impact on the stability of formulations is becoming increasingly important as new coatings are being created, targeted for very specific extended temperature-range environments. This paper will also introduce a new and unique capability for fully-automated freeze & thaw emulsion and dispersion stability analysis experiments.