Reconfigurable Microfluidic Droplets Stabilized by Nanoparticle Surfactants

Interfacial assemblies of nanoparticles can stabilize liquid–liquid interfaces. Due to the interactions between functional groups on nanoparticles dispersed in one liquid and polymers having complementary end-functionality dissolved in a second immiscible fluid, the anchoring of a well-defined number of polymer chains onto the nanoparticles leads to the formation of NP–surfactants that assemble at the interface and reduce the interfacial energy. We have developed droplet interfaces covered with elastic, responsive monolayers of NP–surfactants. Due to the presence of an elastic layer at the interface, the droplets offer a greater resistance to coalescence and can prevent the exchange of materials across interfaces. Our results show the successful encapsulation of nanoparticles, dyes, and proteins with diameters in the 2.4–30 nm range. Further, we show that stable water-in-oil droplets can be generated for various combinations of polymer ligands and nanoparticles bearing complementary functionalities. These NP–surfactant-stabilized microfluidic emulsions would enable applications requiring liquid–liquid interfaces that can adapt and respond to external stimuli and whose mechanical properties can be easily tailored.