(86e) Interfacial Activity of Isotropic Particles in Fluid-Fluid Interfaces

Surfactants can adsorb in fluid-fluid interfaces and lower the interfacial tension. Like surfactants, particles with appropriate wettability can also adsorb in fluid-fluid interfaces. Despite many studies of particle adsorption at fluid interfaces, there has been a long ongoing debate whether isotropic particles can reduce the interfacial tension. In the present work, the interfacial activity of isotropic silica nanoparticles for air-water and hexadecane-water interfaces was analyzed through pendant drop tensiometry. Our measurements show that isotropic particles can change interfacial tensions provided that they have a strong affinity to an interface by virtue of their wettability and that no energy barriers to adsorption prevent them from reaching the interface. In addition, a simple thermodynamic model was used to estimate the effective interfacial tension accounting for particle adsorption; its predictions are consistent with experimental data presented. Finally, we suggest that dynamic interfacial tension measurements, when combined with information about the particlesâ?? wetting properties, provide a convenient and accurate way to assess the packing density of particles in fluid-fluid interfaces. These results will be useful for understanding and controlling the assembly of isotropic nanoparticles at fluid-fluid interfaces relevant to applications ranging from surfactant-free formulations and food technology to oil recovery.