Effects of Hydrophobic Phase Properties on Controlling Nanoparticle Jamming at Oil/Water and Air/Water Interfaces

Fluid/fluid interfaces stabilized with strongly adsorbed solid nanoparticles are implemented in industries including cosmetics, pharmaceuticals, and food science. Solid particles at the interface result in complex interfacial mechanics, which are highly dependent on interfacial particle behavior and bulk properties of both fluid phases. Many interfacial studies have been conducted characterizing the effects of the aqueous fluid properties such as particle chemistry, pH, temperature, salinity, and the impact of surfactant and other additives on interfacial mechanics and adsorption behavior. However, the role of the hydrophobic phase on interfacial stability, as well as the adsorption and organization of interfacial material, is less understood. In this work, mechanical properties of particle-laden interfaces are characterized at oil/water and air/water interfaces to determine the impact of the hydrophobic fluid on particle jamming at the fluid/fluid interface. A model aqueous phase containing CTAB-SiO₂ (cationic surfactant-anionic nanoparticle) complexes is used to deliver particles to air/water, dodecane/water, and silicone oil/water interfaces using a fixed adsorption protocol. Adsorption dynamics and interfacial rheology are measured on microscale using a microtensiometer platform. Results show that under the same aqueous conditions, the hydrophobic phase impacts the effective areal coverage of particles at the interface. When subjected to nonlinear compression cycles, interfacial jamming is impacted by particle wettability and electrostatic interactions between adsorbed particles. These findings suggest that the nonpolar phase has a significant impact on the lateral interactions between particles at the interface. This work highlights how changes to the hydrophobic fluid introduce additional complexities to the interfacial properties and further the understanding of solid particle interactions at different fluid interfaces for controlled emulsion design.