Confined Catalytic Janus Swimmers in a Crowded Channel: Geometry‐Driven Rectification Transients and Directional Locking

Abstract

Self-propelled Janus particles, acting as microscopic vehicles, have the potential to perform complex tasks on a microscopic scale, suitable, e.g., for environmental applications, on-chip chemical information processing, or in vivo drug delivery. Development of these smart nanodevices requires a better understanding of how synthetic swimmers move in crowded and confined environments that mimic actual biosystems, e.g., network of blood vessels. Here, the dynamics of self-propelled Janus particles interacting with catalytically passive silica beads in a narrow channel is studied both experimentally and through numerical simulations. Upon varying the area density of the silica beads and the width of the channel, active transport reveals a number of intriguing properties, which range from distinct bulk and boundary-free diffusivity at low densities, to directional "locking" and channel "unclogging" at higher densities, whereby a Janus swimmer is capable of transporting large clusters of passive particles.

Visible Light Actuated Efficient Exclusion Between Plasmonic Ag/AgCl Micromotors and Passive Beads

“…Simulations : The motion of active micromotors characterized by the self‐propelled velocity v as well as passive beads with v = 0 was simulated by numerically integrating the following overdamped Langevin equationsfor i,j running from 1 to the total number N of particles, active and passive, in the system. Here, μ is the mobility of Janus particles, ξ i 0 ( t ) = ( ξ i 0, x ( t ), ξ i 0, y ( t )) is a 2D thermal Gaussian noise with correlation functions 〈ξ 0, α ( t )〉 = 0, 〈ξ 0, α ( t )ξ 0, β ( t )〉 = 2 D T δ αβ δ ( t ), where α,β = x,y , and D T is the translational diffusion constant of a passive particle of the same geometry as an active micromotor, at a fixed temperature; ξ θ ( t ) is an independent 1D Gaussian noise with correlation functions 〈ξ θ ( t )〉 = 0 and 〈 ξ θ ( t ) ξ θ (0)〉 = 2 D R δ( t ) that models the fluctuations of the propulsion angle θ.…”

“…The last term in the first two equations, , represents, in a compact form, the sum of all interparticle interaction forces in the system. These interactions, in particular, include: i) elastic soft‐core repulsive interactions between active particles, between passive beads, as well as between active and passive particles; ii) the experimentally observed short‐range attraction among particles leading to their aggregation in “molecules” and clusters; and iii) effective repulsive interaction between Janus particles and passive beads, due to the radial flow of products of chemical reaction from the surface of Ag/AgCl Janus particles when being illuminated by blue light.…”

“…The interaction between particles of any sort, active or passive, during the collisions, i.e., the core‐to‐core interaction, is modeled by an elastic repulsive forcewhere R i,j and are, correspondingly, the radius and the position of the i ( j )th particle, and k is the spring constant of the elastic repulsive interaction. The experimentally observed adhesion among Janus particles and silica beads (due to the electrostatic attraction and possibly other mechanisms) is modeled by an additional effective short‐range attractive force termwhere ...…”

Fabrication of Self‐Propelled Micro‐ and Nanomotors Based on Janus Structures

“…Similarly,P t ÀSiO 2 Janus motors were demonstrated to be capable of propulsion in a crowdeda nd confined environment, similar to that in biosystems. [50] This special experimental setup inspired the design of novel motors to perform diverset asks. For example, silica colloids sputtered with Ti and Pt could aggregate and passively power larger engineeredo bjects, such as microgears.…”

Communication: Cargo towing by artificial swimmers

“…[9][10][11] Among the prominent applications of artificial microswimmers and JP's, in particular, is their usage as motors, whereby they couple to a cargo, represented by a passive particle (PP), and tow it from a docking to an end station, often following a meandering path across a crowded environment. 12 In such a configuration, tower and cargo form a dimer with one active head, the JP, and a swerving tail, the PP. 7,9 Biologists observed 13 that active swimmers can act either as pullers, with cargoes trailing them, or as pushers, with cargoes positioned in front of them.…”