Tuning the random walk of active colloids: from individual run-and-tumble to dynamic clustering
Hamid Karani, Northwestern

Active particles such as swimming bacteria or self-propelled colloids spontaneously self-organize into large-scale dynamic structures. The emergence of these collective states from the motility pattern of the individual particles, typically a random walk, is yet to be probed in a well-defi ned synthetic system. Here, we report the experimental realization of tunable colloidal motion that reproduces run-and-tumble and Lévy trajectories. The colloid "run" is powered by the Quincke rotation, i.e., the spontaneous spinning of a dielectric particle polarized in weakly conducting fluid subjected to a uniform electric field. We harness the relaxation nature of polarization in the Quincke effect to achieve controlled sequences of "tumbling" (random reorientations) in the colloid trajectory. We find that population of these Quincke random walkers exhibit behaviors reminiscent of bacterial suspensions such as dynamic clusters.