Texture and stability of emulsions and suspensions: role of oscillatory structural forces.

The stability of macro-dispersions, such as emulsions and particle suspensions, is characterized in different ways-creaming or sedimentation, flocculation of drops/particles, coalescence between drops or phase separation. Several novel experimental techniques have been developed in our laboratory to examine both the texture and stability of emulsions and suspensions. These methods include direct image analysis to extract the emulsion radial distribution function and to determine the effective inter-droplet interaction, and the Kossel diffraction technique, which is used to obtain the structural factors. The film thinning interferometric technique employing our capillary force balance is used to study the role of the surfactant micelles/colloidal particle-layering phenomenon and the in-layer structure formation. Monte Carlo simulations and a theoretical model based on the Ornstein-Zernike equation of statistical mechanics are used to discern the effects of the micelle/particle structuring and layering phenomenon in confined films between two droplets/particles. These experiments and theoretical calculations are used to gain a fundamental understanding of the role of long-range oscillatory (repulsion/attraction) structural interactions on the stability of both mono- and polydispersed systems. During the past 10 years, our research group has worked on several problems of interest to industry in which structural forces in emulsions and suspensions appear to play an important role. This paper is an overview of some of these relevant examples.