Controlling Adsorption of Surfactants, Polymers and Particles to Fluid/Fluid Interfaces with Interfacial Processing

The properties of fluid/fluid interfaces control interfacial phenomena like wetting, foaming and coalescence. Interfacial properties like interfacial tension and dilatational elasticity vary with fluid choice and with the concentration, chemistry and structure of surface-active species adsorbed to the interface. Classical experiments of adsorption are useful to quantify surface activity with simple surfactants but are lacking for more complex systems. Furthermore, common tests of surface activity are often insufficient to describe interfacial phenomena as the phenomena introduce additional timescales that go uncaptured by classical experiments. To control interfacial phenomena, experiments must be augmented by processes that introduce timescales controllable by the researcher.

In this thesis, tools for interfacial processing are developed both to quantify adsorption in complex systems and to control an elusive interfacial phenomenon, spontaneous emulsification. Simple interfacial processing tests adsorption reversibility and better defines the adsorption of simple surfactants, polymers and colloidal particles. Strongly adsorbing species like polyelectrolytes and nanoparticles form irreversibly adsorbed layers at fluid/fluid interfaces. These layers can be processed with solvent, salt solutions and surfactants. Processing can be used on the front end to drive the adsorption of solvent-responsive molecules. By decreasing solvent quality, amphiphilic polypeptoids can be driven and eventually stranded at air/water interfaces. Finally, interfacial processing is used to control the rate of spontaneous emulsification, necessary to determine the mechanism behind the complex phenomenon.