Chemically active colloids near osmotic-responsive walls with surface-chemistry gradients

Abstract

Chemically active colloids move by creating gradients in the composition of the surrounding solution and by exploiting the differences in their interactions with the various molecular species in solution. If such particles move near boundaries, e.g., the walls of the container confining the suspension, gradients in the composition of the solution are also created along the wall. This give rise to chemi-osmosis (via the interactions of the wall with the molecular species forming the solution), which drives flows coupling back to the colloid and thus influences its motility. Employing an approximate "point-particle" analysis, we show analytically that -- owing to this kind of induced active response (chemi-osmosis) of the wall -- such chemically active colloids can align with, and follow, gradients in the surface chemistry of the wall. In this sense, these artificial "swimmers" exhibit a primitive form of thigmotaxis with the meaning of sensing the proximity of a (not necessarily discontinuous) physical change in the environment. We show that the alignment with the surface-chemistry gradient is generic for chemically active colloids as long as they exhibit motility in an unbounded fluid, i.e., this phenomenon does not depend on the exact details of the propulsion mechanism. The results are discussed in the context of simple models of chemical activity, corresponding to Janus particles with "source" chemical reactions on one half of the surface and either "inert" or "sink" reactions over the other half.

23 pages, 2 figures

References in corpus (20)

• The hydrodynamics of swimming microorganisms
• Self-motile colloidal particles: from directed propulsion to random walk
• Motility-Induced Phase Separation
• Physics of Microswimmers - Single Particle Motion and Collective Behavior
• Meso-scale turbulence in living fluids
• Propulsion of a molecular machine by asymmetric distribution of reaction--products
• Designing phoretic micro- and nano-swimmers
• Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations
• Gravitaxis of asymmetric self-propelled colloidal particles
• Giant amplification of interfacially driven transport by hydrodynamic slip: diffusio-osmosis and beyond
• Phoretic self-propulsion at finite Péclet numbers
• Nonequilibrium equation of state in suspensions of active colloids
• Artificial Rheotaxis
• Phoretic Motion of Spheroidal Particles Due To Self-Generated Solute Gradients
• Light Activated Self-Propelled Colloids
• Viscous Marangoni propulsion
• Self-assembly of Active Colloidal Molecules with Dynamic Function
• Autophoretic locomotion from geometric asymmetry
• Pulling and Pushing a Cargo With a Catalytically Active Carrier
• Thermally driven Marangoni surfers

Cited by in corpus (1)

• Shape-dependent guidance of active Janus particles by chemically patterned surfaces