Interfacial Assembly and Jamming Behavior of Polymeric Janus Particles at Liquid Interfaces*

The self-assembly and interfacial jamming of spherical Janus nanoparticles (JNPs) at the water/oil interface is presented. Polymeric JNPs, made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate)(PS-PB-PMMA), with a high interfacial activity assemble at the water/oil interface. Even though none of the building blocks are water soluble, JNPs can self-assemble at interface, prevent direct contact between water and oil, and reduce interfacial energy. Unlike hard particles, the JNPs are composed of polymer chains that can reconfigure at the liquid−liquid interface to maximize coverage at relatively low areal densities of the JNPs. Interpenetration of the polymer chains causes the JNPs to form a solid-like interfacial assembly, resulting in the formation of wrinkles when the interfacial area is decreased. The wrinkling behavior, the retention of the wrinkles, or the slow relaxation of the liquid drop back to its original equilibrium shape was found to depend upon the pH. The soft characteristic of this polymeric JNPs arouse interesting interfacial behavior that has not been found with hard nanoparticles at liquid interfaces.