Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering

Abstract

Micron-sized particles moving through a solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry.

Self-diffusiophoresis of chemically active colloids

“…The study in Ref. [45] has provided evidence for similar states for more complex model systems, e.g., particles with different phoretic mobilities over the catalytic and inert parts. As an example, in Figs.…”

“…(10) the no-slip boundary condition at the wall; using the Lorentz reciprocal theorem directly in the form of Eq. (13) (which is possible since the corresponding integrals over the surface of the wall vanish due to the no-slip boundary condition in both the active particle and the auxiliary problem) [45]. For a uniform phoretic mobility b < 0 (i.e., repulsive interactions between the solute and the colloid), one can indeed find two types of such surface bound states if sufficiently more than half of the particle surface is covered by catalyst (see Fig.…”

“…Second, hydrodynamically the particle creates disturbance flows in the fluid, and these flows are reflected by the no-slip boundary at the walls, coupling back to the particle. The feedback loop between sensing and response is expected to depend on the surface chemistry (e.g., how much of the surface of the particle is covered by catalyst), and can give rise to a rich behavior comprising, in particular, certain surface bound, stable steady-states of motion [45].…”

“…(10) and u a (the so called "auxiliary problem") to be the flow corresponding to a chemically inert particle (i.e., no phoretic slip: u (a) s = 0) moving with prescribed velocities V a and Ω a . Such an auxiliary problem can be straightforwardly solved either analytically (for simple shapes like spheres or spheroids) or numerically (e.g., by using the Boundary Element Method (BEM) [45,69]). The domain in our case is delimited by S δ S P and the surface S ∞ at infinity.…”

The Transport Performance of Feedback Coupled Brownian Ratchets

“…There are some work of the directed transport for Brownian ratchets [6,7] The main concern of this paper is the directed transport properties of the feedback coupled Brownian ratchets under the external force and the effect of coupling.…”