Chemotactic behavior of a self-phoretic Janus Particle near a chemically emitting patch.

Self-phoretic Janus Particles (JPs) are artificial microparticles that aim at reproducing the motion of biological microswimmers (S. Michelin and E. Lauga, J. Fluid Mech. 747, 572 (2014)), such as sperm cells, microalgae, and bacteria, among others. They possess the ability to self-propel in fluids by modifying the chemical composition of the surrounding solution. This results in an effective slip on the particle surface, which can drive the net motion of the JPs. Motivated by the behavior of the biological counterparts which sense and respond to an external chemical gradient (i.e., exhibit chemotaxis), this study aims at modeling the motion of a self-phoretic JP in a non-uniform fuel gradient under geometric confinement. The fuel molecules are released into the solution by a chemically emitting patch located on a planar solid boundary. The particle, moving at very low Reynolds numbers in a Newtonian fluid, steers towards or away from the patch through the interplay of self-diffusiophoresis and chemotaxis. The influence of multiple parameters, such as the activity function, fuel function, catalyst coverage, and patch geometry, is reported. Finally, we address how these states are affected by thermal fluctuations.