(315f) Bubble-Propulsion of Colloidal Dimers in Hydrogen Peroxide

Platinum-coated Janus spheres have shown self-propelling behavior in hydrogen peroxide. However, they were typically produced by template-assisted method with simple symmetry. By utilizing the surface anisotropy of colloidal dimers, we have successfully coated one lobe with platinum nanoparticles via a scalable synthetic route. More interestingly, this type of dimers have shown much stronger propulsion than Janus spheres in hydrogen peroxide solutions due to bublle propulsion. The speed of dimers can be as high as ~53 μm/s (~13 body length/s). Both linear and circular movement were observed, depending on the position where bubbles are generated. For example, when the center of the bubble is along with the long axis of the dimer, it moves in a linear trajectory. Otherwise, circular movement is observed. The rotational direction (either clockwise or counter-clockwise) can also be predicted, based on the torque that a dimer experiences. Analyses from high speed camera images also reveal intriguing modes of bubble propulsion. Both pull-back and push-out have been observed. Our study is the first report for the bulk-synthesis of catalytic micro-motors. The rich propelling behavior reported here could help gain deeper understanding on the propulsion mechanisms of microparticles in solution, which are important for applications in mutli-tasking drug delivery agents and sensors.