Dynamics and separation of circularly moving particles in asymmetrically patterned arrays

Abstract

There are many examples of driven and active matter systems containing particles that exhibit circular motion with different chiralities, such as swimming bacteria near surfaces or certain types of self-driven colloidal particles. Circular motion of passive particles can also be induced with an external rotating drive. Here we examine particles that move in circles and interact with a periodic array of asymmetric L-shaped obstacles. We find a series of dynamical phases as a function of swimming radius, including regimes where the particle motion is rectified, producing a net dc motion. The direction of the rectification varies with the swimming radius, permitting the separation of particles with different swimming radii. Particles with the same swimming radius but different chirality can also move in different directions over the substrate and be separated. The rectification occurs for specific windows of swimming radii corresponding to periodic orbits in which the particles interact one or more times with the barriers per rotation cycle. The rectification effects are robust against the addition of thermal or diffusive effects, and are in some cases even enhanced by these effects.

Dynamical density functional theory for circle swimmers

“…Apart from that, near surfaces bent self-propelled objects tend to follow circular trajectories [42,43]. In modeling approaches, circle swimmers are often realized by simply imposing an effective torque or rotational drive in addition to the self-propulsion mechanism [15,31,35,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59].…”

“…We have mentioned above that studies on circle swimmers are relatively rarely encountered when compared to the numbers of works on objects propelling straight ahead. Even less frequent are studies on the collective behavior of circle swimmers [29,43,50,52,54]. Particularly, this applies when hydrodynamic interactions in crowds of suspended microswimmers are to be included.…”

Simulation of the active Brownian motion of a microswimmer

“…26,41 This is a particularly interesting option because it may provide a better technique to separate molecules with opposite chirality by chemically coupling them to chiral propellers, sorting the resulting chiral microswimmers, and finally detaching the propellers. Such techniques could be applied in the biochemical and pharmaceutical industry where often only one specific chirality is desired.…”

Gaussian memory in kinematic matrix theory for self-propellers

“…Velocity fluctuations lead to stochastic variation of speed, which may also have memory. The direction of motion may be influenced by stochastic noises arising from environmental fluctuations (e.g., Brownian kicks from fluid particles to a micron-sized self-propeller [41][42][43], spatially scattered food supply [60], or interaction with a substrate [61]) or internal fluctuations such as stochastic internal engine torque or decision-making processes of an organism.…”