Hydrodynamic stresses in a multi-species suspension of active Janus colloids

A realistic description of active particles should include interactions with the medium, commonly a momentum-conserving simple fluid, in which they are suspended. In this work, we consider a multispecies suspension of self-diffusiophoretic Janus colloids interacting via chemical and hydrodynamic fields. Through a systematic coarse-graining of the microscopic dynamics, we calculate the multicomponent contribution to the hydrodynamic stress tensor of the incompressible Stokesian fluid in which the particles are immersed. For a single species, we find that the strength of the stress produced by the gradients of the number density field is determined by the particles' self-propulsion and chemotactic alignment, and can be tuned to be either contractile or extensile. For a multispecies system, we unveil how different forms of activity modify the stress tensor and how it can acquire nonreciprocal couplings due to phoretic effects.