  To fully harness the potential of artificial active colloids, investigation
of their response to various external stimuli including external flow is of
great interest. Therefore, in this study, we perform experiments on SiO2-Pt
Janus particles suspended in an aqueous medium in a capillary subjected to
different shear flow rates. Particles were propelled using varied H2O2 (fuel)
concentrations. For a particular propulsion speed, with increasing shear flow,
a transition of motion of active Janus particles from the usual random active
motion to preferential motion across stream-lines and then finally to migration
along the flow, was observed. Our analysis revealed that these transitions are
dictated by the torque due to the self-propulsion near wall w.r.t.
shear-induced torque. Interestingly, we found that only when these torques are
comparable, particles align in a manner such that they migrate significantly
across the streamlines.
