Sideways propelled bimetallic rods at the water/oil interface.

The motion of self-propelling microswimmers is significantly affected by confinement, which can enhance or reduce their mobility and also steer the direction of their propulsion. While their interactions with solid boundaries have already received considerable attention, many aspects of the influence of liquid-liquid interfaces (LLI) on active particle propulsion still remain unexplored. In this work, we studied the adsorption and motion of bimetallic Janus sideways propelled rods dispersed at the interface between an aqueous solution of hydrogen peroxide and oil. The wetting properties of the bimetallic rods result in a wide distribution of their velocities at the LLI. While a fraction of rods remain immotile, we note a significant enhancement of motility for the rest of the particles with velocities of up to 8 times higher in comparison to those observed near a solid wall. Liquid-liquid interfaces, therefore, can provide a new way to regulate the propulsion of bimetallic particles.

Electroless Deposition of Silver onto Silica Nanoparticles to Produce Lipophilic Core-Shell Nanoparticles.

HYPOTHESIS: The colloidal stability of noble metal nanoparticles can be tuned for solvents of varying hydrophobicity by modifying the surface chemistry of the particles with different capping agent architectures. Challenges arise when attempting to separately control multiple nanoparticle properties due to the interdependence of this adsorption process on the surface chemistry and metal architecture. A surfactant-mediated, templated synthesis strategy should decouple control over size and stability to produce lipophilic nanoparticles from aqueous reagents. EXPERIMENTS: A modified electroless plating process that produces oil-dispersible core-shell silver-silica nanoparticles is presented. Amine-terminated alkanes are utilized as the capping agents to generate lipophilic surface coatings and the particles are temporarily stabilized during the synthesis by adding a Pluronic surfactant that enhances dispersibility in the aqueous reaction medium. The evolution of shell morphology, composition, and colloidal stability was analyzed against capping agent architecture and concentration. The role of particle shape was also tested by interchanging the template geometry. FINDINGS: The capping agents installed on the silver shell surface displayed both colloidal stability enhancements and a minimum effective capping concentration that is a function of molecular weight without influencing the shell composition. Particle geometry can be controlled by interchanging the silica template size and shape.

'Sweeping rods': cargo transport by self-propelled bimetallic microrods moving perpendicular to their long axis.

A possible application of self-propelling particles is the transport of microscopic cargo. Maximizing the collection and transport efficiency of particulate matter requires the area swept by the moving particle to be as large as possible. One such particle geometry are rods propelled perpendicular to their long axis, that act as "sweepers" for collecting particles. Here we report on the required Janus coating to achieve such motion, and on the dynamics of the collection and transport of microscopic cargo by sideways propelled Janus rods.