Forced desorption of nanoparticles from an oil-water interface.

While nanoparticle adsorption to fluid interfaces has been studied from a fundamental standpoint and exploited in application, the reverse process, that is, desorption and disassembly, remains relatively unexplored. Here we demonstrate the forced desorption of gold nanoparticles capped with amphiphilic ligands from an oil-water interface. A monolayer of nanoparticles is allowed to spontaneously form by adsorption from an aqueous suspension onto a drop of oil and is subsequently compressed by decreasing the drop volume. The surface pressure is monitored by pendant drop tensiometry throughout the process. Upon compression, the nanoparticles are mechanically forced out of the interface into the aqueous phase. An optical method is developed to measure the nanoparticle area density in situ. We show that desorption occurs at a coverage that corresponds to close packing of the ligand-capped particles, suggesting that ligand-induced repulsion plays a crucial role in this process. © 2011 American Chemical Society

Scalable Synthesis of Janus Particles with High Naturality

Because of the increasing concerns about the ecological damage and negative health effects that may be caused by petrochemical-based microbeads, many countries are banning their use in a wide range of consumer products. One particular class of particles that may never reach their full potential because of such a ban is Janus particles, which are particles with two opposite properties. Despite significant progress in the scalable synthesis of Janus particles, most studies rely on petrochemical-based materials and solvents to enable their synthesis. In this report, we present a single-emulsion polymerization method for scalable synthesis of amphiphilic Janus particles with materials derived from plants. Soybean oil-epoxidized acrylate (SBOEA) monomers are polymerized in single-emulsion droplets of SBOEA, ethyl cellulose (EC), butyl acetate, and initiators that can be generated by either bulk or microfluidic emulsification, leading to the formation of amphiphilic soybean oil polymer/EC (SBOP/EC) Janus particles. Interfacial anchoring of the in situ-formed SBOP particles at the interface of the emulsion droplet plays a key role in the formation of the SBOP/EC Janus particles. Large-scale preparation of uniform SBOP/EC Janus particles is also demonstrated using a glass-silicon microfluidic device. Finally, the SBOP/EC Janus particles show potential to stabilize oil-in-water emulsions that can stay stable under flowing conditions

Self-assembly of uniform polyhedral silver nanocrystals into densest packings and exotic superlattices

Understanding how polyhedra pack into extended arrangements is integral to the design and discovery of crystalline materials at all length scales. Much progress has been made in enumerating and characterizing the packing of polyhedral shapes, and the self-assembly of polyhedral nanocrystals into ordered superstructures. However, directing the self-assembly of polyhedral nanocrystals into densest packings requires precise control of particle shape, polydispersity,interactions and driving forces. Here we show with experiment and computer simulation that a range of nanoscale Ag polyhedra can self-assemble into their conjectured densest packings. When passivated with adsorbing polymer, the polyhedra behave as quasi-hard particles and assemble into millimetre-sized three-dimensional supercrystals by sedimentation.We also show, by inducing depletion attraction through excess polymer in solution, that octahedra form an exotic superstructure with complex helical motifs rather than the densest Minkowski lattice. Such large-scale Ag supercrystals may facilitate the design of scalable three-dimensional plasmonic metamaterials for sensing, nanophotonics, and photocatalysis