(206h) Targeted Delivery of Surfactants Via Directed Assembly of Nanoparticles at Liquid-Liquid Interfaces By Fine-Tuning Molecular Interactions

A system that combines into a single platform, both controlled assembly and targeted delivery, is demonstrated for the first time. The directed assembly of positively-charged, amine-functionalized polystyrene nanoparticles, PS NPs, at the oil/water interface was accomplished by introducing carboxylic acid functional groups in the oil phase. The electrostatic interactions between the ammonium groups on the NPs and the carboxylic groups on the oil surface was supported by zeta potential measurements and confirmed by laser scanning confocal microscopy. In contrast, negatively-charged, sulfonate-functionalized PS NPs fail to assemble at the interface and remain in the aqueous phase under the same conditions. By tuning the pH or the ionic strength of the medium, we were able to modulate the extent of the interactions between the NPs and the oil surface. After assembly at the oil-water interface, the NPs can release appropriately loaded cargo including surfactant molecules. The released surfactant leads to the formation of a much finer oil-water emulsion. This unique design feature can be exploited in various applications in fields ranging from pharmaceutical and cosmetics to hydrocarbon recovery and oil-spill remediation.