Acceleration and deceleration of a conductive particle within parallel electrodes in viscous fluid

Careful examination of the motion of a conductive particle under uniform electric field in viscous fluid revealed that there are four regimes, namely, acceleration, constant speed, deceleration and settling on the electrodes. Since each regime shows different character depending on size and density, applied voltage and viscosity of fluid, the particle motion was observed by using an ordinary CCD and a high-speed cameras. As a conductive particle, a steel ball and a glassy carbon particle were used. In the case of a glassy carbon particle, settling time on both electrodes is quite long compared with a steel ball because of the difference of density. However, the settling on the upper electrode was observed even with a steel ball, that cannot be expected normally. A particle is accelerated by electric field after leaving the electrode and then reaches almost constant speed. When the particle approaches the counter electrode, it is decelerated by viscous drag. Average velocity between electrodes changes with the viscosity of fluid. The measured results were compared with theoretical analysis of a particle motion by taking account of viscous effect.