Polymeric Janus Nanoparticles at Water/Oil Interfaces

We present a study on the assembly of polymeric Janus nanoparticles (pJNPs) at the toluene/water interface. The soft spherical polymeric Janus nanoparticles pJNPs, made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (PS-PB-PMMA), show a high interfacial activity, even though neither component is soluble in water. The preferential affinity of the PMMA to the aqueous phase causes a spreading of the PMMA block at the interface. Unlike hard NPs where, after the interfacial tension has decreased and stabilized, only a small volume reduction of the pendant droplet is required to induce wrinkling, for soft pJNPs, there must be a significant reduction in the pendant drop volume to induce wrinkling. A series of pJNPs where the molecular weight at constant weight fraction or where the weight fraction at constant molecular weight of the brushes and cores were varied to probe the influence of molecular weight, brush lengths and volume fractions of the component arms on the areal density of the assemblies and the response of the assemblies to a compression. We also investigated the influence of metal ions in the aqueous phase that can complex with the PMMA on the assembly, packing, stability and responsiveness of pJNP assemblies.