Dynamic Interactions between Fast Microscale Rotors

Trimetallic catalytic microrotors were fabricated by electrodeposition of cylindrical Au-Ru rods in the pores of anodic alumina membranes, dissolution of the template membrane, and then sequential vapor deposition of Cr, SiO2, Cr, Au, and Pt on one side of each rod. This design provides two force vectors for the catalytic motor, including one perpendicular to the rod axis. The rods rotated rapidly (similar to 180 rpm) in 15% aqueous H2O2 solution with minimal orbital or translational movement. The rotation was rapid enough to observe qualitatively different interactions between pairs of co- and counter-rotating rods. Counter-rotating rods were able to approach each other closely and underwent frequent tip-to-tip collisions. Co-rotating rods could approach each other only to a distance of similar to 0.9 mu m. This difference is rationalized on the basis of shear forces generated by the catalytically driven rotation of the rods.