This year (2014) we celebrate a decade anniversary of catalytic micromotors, in which they have come to represent one of the important technical advances, having shown promise in many important functions in biomedical and engineering fields such as sensing, detection, drug delivery, oil spill cleanup, etc. Catalytic nano-/ micromotors are structures that convert chemical energy present in the surrounding aqueous environment into mechanical work through a catalytic reaction induced by an asymmetrically placed catalyst. In this talk, we will look into different driving mechanisms of micromotors. The focus will be on bubble propulsion and it’s fundamentals.

The bubble propulsion mechanism is observed when the bubbles formed on the catalyst surface eject or burst. The motion of bubbles provides an opposing thrust to the motor. We have studied the motion of bubble propelled big Janus motors using a fast CCD camera. The formation of bubbles depends closely on the nucleation energy, which also is related to surface curvature. It is predicted that bubbles are easier to nucleate on a concave shaped surface than on a convex shaped surface. Thus, bubble propulsion can be easily seen in concave motors. The predictions were confirmed with nanoshell catalytic motors with catalyst coated inside the shell. Similarly, if the catalyst is coated in the inner surface of a tube, a tubular motor can be produced. We used graphene oxide nanosheets (GO) as templates and the stress effect in the multilayer of metal thin films to create microtubes.

Finally, collective motion with micromotors has emerged as an important concept. Collevtive behavior is observed through out the nature and can be emulated in the micromotor world. Using different properties of motional behaviors of motors, motors can be designed to perform tasks collectively. This can ultimately help in increasing the efficiency of completing tasks. We observe a unique collective bubbling with 5-μm diameter Janus motors. The bubbling has always been observed with individual motors, however, for the first time we observe bubble production through a collective effort.