Interfacial\nAssembly and Jamming Behavior of Polymeric Janus Particles at Liquid\nInterfaces

Abstract

The\nself-assembly and interfacial jamming of spherical Janus nanoparticles\n(JNPs) at the water/oil interface were investigated. Polymeric JNPs,\nmade by cross-linking polystyrene-<i>block</i>-polybutadiene-<i>block</i>-poly­(methyl methacrylate) (PS-PB-PMMA), with a high\ninterfacial activity assemble at the water/oil interface. During the\nself-assembly at the interface, the interfacial energy was reduced\nand a dynamic interlayer was observed that is responsive to the pH\nof the aqueous phase. Unlike hard particles, the JNPs are composed\nof polymer chains that can spread at the liquid–liquid interface\nto maximize coverage at relatively low areal densities. In a pendant\ndrop geometry, the interfacial area of a water droplet in oil was\nsignificantly decreased and the JNPs were forced to pack more closely.\nEntangling of the polymer chains causes the JNPs to form a solid-like\ninterfacial assembly, resulting in the formation of wrinkles when\nthe interfacial area is decreased. The wrinkling behavior, the retention\nof the wrinkles, or the slow relaxation of the liquid drop back to\nits original equilibrium shape was found to depend upon the pH.