The effect of particle size on the dynamics of self-electrophoretic Janus micromotors, sputtering distribution, and rectifying voltage

Micromotors have gained increasing attention in last two decades, due to their controllable self-propulsion maneuverability at micro scales. However, the effect of particle size on micromotors is still vague and interwoven due to the micromotors’ size, polydisperse distribution, and structural variations. Microfluidic technology is used to clarify the phenomenon, due to its precise micro scale fabrication. Herein, we fabricated a H₂O₂-driven self-electrophoretic Janus micromotor and systematically explored the effects of particle size on their dynamics, the sputtering distribution, and the rectifying voltages. Their speeds were found to be inversely proportional to their sizes. When the particle size was fixed, their speeds increased as coating thickness increased until its hemisphere was fully coated, and this critical coating thickness was also proportional to the sizes of the micromotors. As further investigation goes on, we noticed that electrical voltage to rectify micromotor was proportional to its size too. To summarize, our results showed that larger micromotors moved more slowly, required a thicker metal coating to reach full speeds, and needed higher voltages to be rectified. Through all of these investigations, we believed that microfluidic technology is a valuable tool, which can systematically probe micromotors dynamics and clarify our understanding of micromotors behaviors.