Properties of Fatty Amine-Silica Nanoparticle Interfacial Layers at the Hexane-Water Interface

The formation and properties of composite layers of silica nanoparticles and an oil-soluble (fatty) amine surfactant at the oil-water interface have been studied using interfacial tensiometry, theology, and contact angle measurements to characterize the synergy between the particles and surfactant. The initially hydrophilic particles interact with the surfactant only at the water-hexane interface. Synergistic interactions are required for interface stabilization. A key result is that nanoparticle attachment is driven by surfactant adsorption at the liquid interface. Particles are efficiently bound to the interface once the adsorbed surfactant layer is close to saturation. Surfactant adsorption onto the particle surfaces optimizes the particle wettability and promotes particle aggregation into networks that enhance the viscoelasticity of the interface. The implications of these results for controlling the formation and kinetic stability of emulsions containing particles and surfactant are discussed.