Effect of Janus particles and non-ionic surfactants on the collapse of the oil-water interface under compression.

Hypothesis: Janus particles (JPs) and surfactants express different behaviors at the oil-water interface under compression. When both are present at the interface, their synergies result in a different collapse mechanism than when present individually depending on the concentration of the JPs and surfactants.

Experiments: Coarse-grained modeling methods were used to probe the synergies between Janus nanoparticles and nonionic surfactants on the stability of an oil-water interface under compression. When both JPs and surfactants were present, the interface was covered at 0-55% area by JPs and contained surfactants at 0-40% of the interfacial surfactant concentration corresponding to the critical micelle concentration (CMC).

Findings: Compression of the interface with only surfactants resulted in the expulsion of surfactant molecules to the water phase once the interfacial concentration of surfactant molecules reached the CMC value. Compression of a Janus particle-laden interface past the closed-packing point led to a buckled interface, so that the total interfacial area remained constant upon further compression. When both surfactants and JPs were present on the interface, JPs still caused buckling, which helped retain the surfactant molecules on the interface. The interface exhibited a higher level of deformation in presence of surfactants. When the surfactant concentration was high, under compression, the surfactants partitioned into the water phase, but the buckling of the interface persisted.