Self-propelled motion of induced-charge electrophoretic Janus particles in viscoelastic fluids.

Abstract

Swimming micro-objects exist in viscoelastic fluids. Elucidating the effect of viscoelasticity on the motion of these objects is important for understanding their behavior. Since the mechanical response of viscoelastic fluids depends on the temporal deformation rate exerted by a moving object, it is necessary to control their speed over a wide range to examine the effect of viscoelasticity. In this study, we examined the motion of Janus particles self-propelled by induced charge electrophoresis over a wide range of speeds in semidilute polymer solutions. In our system, the motion of Janus particles changed from active Brownian motion to stationary rotation as the speed increased. The torque for stationary rotation originates from the difference between the direction of self-propulsion and that of the time-delayed restoring force from the polymer solution, which has been reported in another self-propelled particle system. The switch from active Brownian motion to stationary rotation at different polymer concentrations can be explained by the Weisenberg number, which is defined as the ratio of the relaxation time of the polymer network to the travel time of the Janus particle to its size. The results of this study will lead to a better understanding of the motion of self-propelled micro-objects in viscoelastic fluids.