Harnessing Interfacial Phenomena Involving Macromolecules for Emulsion Processing

An emulsion is a mixture of two immiscible solutions, one dispersed in the other. Intrinsically, most emulsions are thermodynamically unstable and thus active agents called surfactant are added to the mixture to stabilize the interface. The surfactant lowers the interfacial tension and provides steric and/or electrostatic repulsion at the fluid interfaces to enhance the stability of emulsions. Macromolecules, either intrinsically surface active or not, have attracted lots of attention for emulsion processing. On one hand, advances in polymeric synthesis technique present various polymeric surfactants waiting to be exploited. On the other hand, macromolecules present the platform for versatile modification that can result in assemblies with special properties. Various natural materials are also macromolecules, waiting to be exploited as replacements for synthetic surfactants of petrochemical origins. In this thesis, ion pairing and microfluidic techniques are used to expand the macromolecules’ application and to investigate the composition effect of polymeric surfactants in emulsion processing. Polyelectrolyte is extracted into an organic phase via ion pairing with an oppositely charged surfactant. The formed ion pair retain the polyelectrolyte’s capability to form complexes. It complexes with oppositely charged polyelectrolyte and is exploited for one-step polyelectrolyte microcapsules generation. Meanwhile, the composition effect of a set of polymeric surfactants, Pluronics, on flow-induced phase inversion emulsification (FIPIE) is studied. Through microfluidic technology, emulsion phase inversion process at the single droplet level is monitored. We find strong correlation between the molecular weight (MW) and the lengths of individual blocks of the Pluronics and the tendency of droplets to undergo (FIPIE). In Chapter 4, dynamic ion pairing between polyelectrolyte and surfactant is used to induce phase inversion emulsification (PIE). The ion pair formation is controlled as a function of the solution pH and surfactant concentration. Both oil-in-water (O/W) and water-in-oil (W/O) emulsions are formed and PIE from W/O to O/W emulsion is demonstrated. In summary, macromolecules possess rich behaviors at the emulsion interfaces. The macromolecule and surfactant association, such as ion pairing, form assemblies with distinct properties, expanding common materials’ application for versatile emulsion processing