Visualization and measurement of the self-propelled and rotational motion of the Janus microparticles

The self-propelled diffusiophoresis, induced by an asymmetric concentration gradient field, provides a new strategy to manipulate micro-objects (like some cells and colloids) in solutions. One example is the autonomous motion of the double-faced Janus microparticle (platinum coating on one half of a silica particle) due to a chemically catalyzed reaction (reduction of hydrogen peroxide) on the Pt surface. In this paper, a systematic method is developed to describe the details of self-propulsion and rotation of Janus microparticles, despite the difficulty induced by particle non-uniformity. From the measurement, we found that the particles presented a three-stage behavior of the dimensionless mean square displacement, and their displacement probability distribution formed a double-peaked structure. These results show the intrinsic characteristics and the non-Gaussian behavior of Janus particle’s self-propulsion. Furthermore, the rotational motion is characterized by the rotational angle variation and the rotational diffusion coefficient. These results show that Brownian rotation still dominates the Janus microparticle’s rotational motion, though the measured rotational diffusion coefficient presents an anomalous tendency. Graphical Abstract