Mechanism of stabilization of silicone oil-water emulsions using hybrid siloxane polymers

Silicone polymers, due to their high lubricity and good spreading properties, are widely used in industrial applications. Being insoluble in water and most hydrocarbons, a common mode of delivering silicones is in the form of emulsions. To stabilize silicones in the emulsion form more efficiently, it is useful to understand the mechanism of emulsion stabilization. Two different mechanisms of emulsion stabilization have been proposed in the past: film formation and precipitation (known as the Pickering mechanism). These two mechanisms are different, and there is a need to further investigate this issue. The aim of the present work was to investigate the mechanism of stabilizing silicone emulsions and to propose a generalized behavior. Several experiments including the measurement of Langmuir isotherms, rheology experiments, phase diagram studies, and microscopy experiments were conducted. All of the above techniques indicated that the functional groups interact strongly with the water phase. The emulsions were found to be stable only if the emulsifiers were soluble in silicone oil or the water phase, and the stability decreased as the emulsifier precipitated. In most cases tested here, the emulsifiers were not observed to precipitate as reported earlier for the Pickering mechanism, and the emulsion stabilization followed film formation. These results should help to predict emulsion stabilization for unknown systems.