Controlling Properties of Particle-Laden Interfaces Through Interfacial Processing and Design Towards Emulsion Stability

 Strongly absorbed particles significantly impact the mechanical properties of fluid-fluid interfaces, and the interfacial properties of these systems are associated with the formation of highly stable emulsions and foams. Interfacial properties are directly affected by the properties of the aqueous fluid, as well as particle properties which include surface chemistries and aggregation states. The nature of the hydrophobic fluid (most often air or oil) also has a significant impact on the behavior of particles at the interface which is far less understood. To better engineer emulsion systems with desired stability, we need to develop tools necessary to systematically quantify the effects of the hydrophobic fluid on the interfacial mechanics associated with stability at particle-laden interfaces. 

This work uses in-situ techniques that allow for the efficient, detailed characterization of bulk and interfacial properties essential for controlling emulsion stability. A millifluidic technique is shown to be a powerful approach for bulk stability studies in opaque colloidal dispersions and is used here to characterize the long-time solvency effects on asphaltene precipitation. The degree of aggregation and overall stability of asphaltene dispersions is highly dependent on molecular characteristics, bulk concentration, and solvent composition. The complex interfacial behavior of asphaltenes, connected to the development of highly stable water-in-oil emulsions, are defined by these bulk system conditions. 

Controlled experiments using a microtensiometer platform are used to characterize the mechanical properties of particle-laden oil/water interfaces and assess the role of the hydrophobic fluid on particle jamming. This work shows how changing the hydrophobic phase leads to additional complexities in the characterization of the interfacial properties. Additionally, we identify system parameters that can be used to control particle coverage and interactions at the oil/water interface. 

These interfacial studies further the understanding of methods to control adsorption of complex species to oil/water interfaces. The results from this work highlight the significance of the hydrophobic fluid on interfacial behavior at particle-coated interfaces and outline key design considerations for processing and designing interfaces for use in particle-stabilized emulsions. In identifying tools to control and characterize complex interfaces and showing the importance of interfacial processing on interfacial behavior, this work provides important design rules for the engineering of particulate-based interfacial systems.