(225e) Synthesis and Applications of Anisotropic Dimers

Janus or pathy particles have attracted lots of attentions currently due to their wide applications in optical display, emulsion stabilization, biomedical imaging and drug delivery. We have successfully synthesized colloidal dimers with different properties targeting for three different applications: self-assembly, nanomotors, and colloidal emulsifiers.

Dimers with geometric anisotropy showed interesting assembly behaviors, such as chiral structures, under electric fields. While dimers with one lobe coated by platinum are propelled by periodic growth and collapse of bubbles in hydrogen peroxide solution. We find that both high catalytic activity and rough surface are necessary for making bubble propelled micro-motors. Meanwhile, we observed two types of motions from the hybrid dimers: linear and circular motions, which are determined by the relative position of the bubble to the dimer. Although the two motions follow the same growth curve in the bubble growth stage which proved to be a diffusion controlled process, they exhibit opposite behavior at the bubble burst moment. This is because when the bubble collapses asymmetrically due to the influence of the solid substrate, vortex rings develop. The resulting solvent flow could push or pull the dimers depending on the particle locations to the substrate.

As for dimers with interfacial anisotropy or even bulk anisotropy, could be treated as colloidal surfactants. We utilize the bulk anisotropy of the colloidal dimers as a phase delivery agents. We successfully delivered catalysts from water phase to oil phase and performed hydrogenation in oil phase with three different α-olefins.

Our study shows a potential application of colloidal dimers in multiple fields with surface modification or bulk encapsulation. Our investigation in micromotor not only provides insight into the link between self-diffusiophoresis and bubble propulsion, but also reveals the intriguing impacts of the combined geometric and interfacial anisotropy on self-propulsion of particles. In terms of colloidal emulsifier, we find a new type of colloidal surfactant without amphiphilicity.