Abstract
The diffusion of an artificial active particle in a two-dimensional periodic pattern of stationary convection cells is investigated by means of extensive numerical simulations. In the limit of large P\'eclet numbers, i.e., for self-propulsion speeds below a certain depinning threshold and weak roto-translational fluctuations, the particle undergoes asymptotic normal diffusion with diffusion constant proportional to the square root of its diffusion constant at zero flow. Chirality effects in the propulsion mechanism, modeled here by a tunable applied torque, favors particle's jumping between adjacent convection rolls. Roll jumping is signaled by an excess diffusion peak, which appears to separate two distinct active diffusion regimes for low and high chirality. A qualitative interpretation of our simulation results is proposed as a first step toward a fully analytical study of this phenomenon.
Highlights
Microswimmers are Brownian particles capable of selfpropulsion [1,2]
We focus on the phenomenon of advection dominated active diffusion, that is on the dynamical regime where a noiseless achiral Janus particles (JP) would be strictly localized by the stream function ψ (x, y)
Depinning of a noiseless particle from the dynamical trap represented by a single convection roll occurs for self-propulsion speeds above a certain threshold [16]
Summary
Microswimmers are Brownian particles capable of selfpropulsion [1,2]. The simplest category among them consists of artificial micro- and nanopropellers, which, due to some ad hoc asymmetry of their geometry and/or chemical composition, are capable of harvesting environmental energy and convert it into kinetic energy. Artificial microswimmers found promising applications in the pharmaceutical (e.g., smart drug delivery [5]) and medical research (e.g., robotic microsurgery [6]), whereby one expects that the function they are designed to perform is governed in time and space by their diffusive properties To this regard it is important to control the diffusion of active particles in crowded [4] and patterned environments [7], where they interact with other system components, either chemically [8] or mechanically [9]. [16], but only in the noiseless, chaotic limit These authors proved that, for self-propulsion speeds below a certain threshold, the particle gets dynamically trapped inside the convective rolls and its diffusion suppressed. The chiral and shear torque compensate each other inside two diagonally opposite ψ (x, y) subcells; this causes a partial depinning of the active particle from the convection rolls with a consequent diffusivity surge
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