Encapsulation of Active Liquids Using a Pickering Emulsion Platform

Abstract

Emulsions are mixtures of two immiscible fluids, where droplets of one are dispersed in the continuous phase of the other. The stability of emulsions can be improved through the addition of a small molecule surfactant, such as sodium dodecyl sulfate. Alternatively, Pickering emulsions are those that are stabilized by solid particles instead of small molecule surfactants. Of particular interest are Pickering emulsions stabilized by graphene oxide (GO) nanosheets because of the planar nature of the nanosheets and their ability to be both covalently and non-covalently modified. Such chemical modification allows for the wettability of the nanosheets to be tuned to stabilize a variety of emulsion platforms (e.g., not only oil-in-water). Pickering emulsions can be used in conjunction with simple chemistries to prepare a variety of composite structures.

This dissertation advances the preparation and application of GO-stabilized Pickering emulsions as a platform to include a variety of active liquids, specifically task specific ionic liquids (ILs), poly(α-olefins) (PAOs), and deep eutectic solvents (DESs). These liquids are considered “active” as they have unique properties beyond those inherent with being a liquid. However, these active liquids are often very viscous, resulting in slow mass transfer rates and handling difficulties. To overcome such issues, these liquids were successfully encapsulated in a GO/polyurea shell via interfacial polymerization utilizing a Pickering emulsion template. Encapsulation increases the surface area of the active liquid, which facilities mass transfer by making more active liquid accessible (provided permeability of the composite shell), and allows the user to handle the active liquid as a solid, mitigating many handling difficulties. Potential applications of the active liquid capsules were then examined, and a study was done to determine how polymer structure impacts capsule shell permeability to small molecules. Finally, transition metal oxides, another class of 2D nanosheets, were studied as a Pickering emulsion co-surfactant with GO, demonstrating that surfactant composition can also be tailored, opening new opportunities. The work reported here lays a foundation for the use of capsules of active liquids as media for separations and offers insight into how surfactant, discontinuous phase, and polymer choice impact the application of a capsule system.