Active fluids of colloidal Quincke-powered rotors

Self-propelled particles such as swimming bacteria or motile colloids spontaneously self-organize into large-scale dynamic structures that move around like fluid when viewed on a scale much larger than the individuals. A popular means to propel colloids is the Quincke rotation, e.g., by simply letting the particles roll on a surface (Bricard et al, Nature 2013). In this talk, I will show how Quincke rollers can be designed to perform Run-and-Tumble-like locomotion mimicking bacteria such as E. coli (Karani et al, Phys. Rev. Lett. 2019). Populations of these Quincke random walkers self-organize and exhibit behaviors reminiscent of bacterial suspensions such as dynamic clustering and mesoscale turbulent-like flows, and new behaviors such as emergent multi-vortex states (Zhang et al. Soft Matter, 2021). When enclosed in a drop, the Quincke rollers drive strong shape fluctuations and drop motility resembling amoeba crawling (Kokot et al., Comm. Phys, 2022). I will also discuss the Quincke rotors dynamics in free space (an example of physical realization of Lorenz chaos), and in strong confinement, where new periodic motions emerge.