Translational and rotational dynamics of a self-propelled Janus probe in a crowded medium*

Motivated by a series of experiments, we simulate the dynamics of a self-propelled (active) Janus probe in a crowded medium. The crowding is caused either by viscoelastic polymer chains or by non-viscoelastic spherical colloids. Our simulations show enhancement of the translational and rotational dynamics with the self-propulsion velocity but most importantly a three-step growth (diffusive-superdiffusive-diffusive) is also observed in the case of rotational motion of the self-propelled Janus, while crowders are present. This is observed irrespective of whether the crowders are viscoelastic or not, confirming viscoelasticity of the medium is not responsible for this enhanced dynamics, rather it is the presence of crowders. However, in the absence of crowders, rotational dynamics remain practically unaffected as the self-propulsion velocity is changed. At the intermediate area fraction of the crowders, translational and rotational motions of the self-propelled Janus get decoupled. Such decoupling is not observed if the Janus is passive.