Assembly and reformation of structured liquids at the water-oil interface

Nanoparticle-surfactant (NPS) assembled at water− oil interfaces can significantly lower the interfacial tension and reversibly transition from a solid like jammed state to a liquid state enabling the stabilization of non-equilibrium shaped domains of liquids. Understanding the formation and assembly and actively tuning the packing of these NPSs are of fundamental interest for the interfacial behavior of nanoparticles and of interest for water purification, drug encapsulation, enhanced oil recovery, and innovative energy transduction applications. We demonstrate the high ionic strength helps the adsorption of NPSs to the water− oil interface leading to a denser packing of NPSs at the interface by means of the interfacial tension measurement. With the reduction of interfacial area, the phase transitions from a “gas” -like to “liquid” to “solid” states of NPSs in two-dimension are proposed and observed. We show the first in situ real-space imaging of NPSs at the water− oil interface by atomic force microcopy, how different sized NPs compete and affect the pattern of the assembled films, and the generation of nano-patterned fluidics with optical and scanned probe based lithography.