Unravelling Synthesis and Transport Phenomena in Emulsion Systems with Small Angle Scattering
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Emulsions are a dispersion of two immiscible liquids that can be found in a variety of products frequently used in our daily lives. These dispersions of droplets are intrinsically unstable and would phase separate if no stabilizers were present. Even if the emulsions are stabilized, the emulsion system is still extremely dynamic and multiple phenomena could occur simultaneously to affect the stability of the dispersion. Therefore, fundamentally understanding how the droplets interact with each other is crucial when designing emulsion-based products. Small angle scattering is a unique technique that can provide information of a sample in its native environment. Moreover, custom-built sample environments could also be utilized with this technique to provide additional controllable parameters such as the application of acoustic forces to alter the dynamics in emulsion system. Thus, small angle scattering is an optimal method for characterizing emulsion systems. In this dissertation, three different fundamental interactions that occur in emulsion systems are probed using both small angle X-ray scattering and small angle neutron scattering. The role of acoustic forces in solid particle stabilized Pickering emulsion formation using sonication is first investigated. Cavitation events are found to be crucial in inducing particle adsorption onto the oil-water interface. Mass transport kinetics between emulsions are also presented in this dissertation. When the emulsions are at rest, oil molecules can exchange between oil droplets spontaneously by directly diffusing through the aqueous phase or via direct emulsion contact. When emulsions are sonicated, the acoustic-force induced cavitation can significantly accelerate the oil exchange process. Moreover, the electrostatic repulsion, Gibbs elasticity of the oil-water interface provided by the presence of surfactants, and the emulsion size all played a role in the acoustic force induced oil exchange process. This dissertation will demonstrate our work towards understanding the interactions in emulsion systems on a molecular scale to provide a fundamental knowledge on how to design an emulsion-based system.
- Chemical engineering