Electrorotation manipulation of microparticles induced by torque and electroosmotic slip in microsystem

Electrorotation is an effective technique to characterize the electrical properties of dispersed particles. For the low Reynolds number microsystem, the mechanism of the electrorotation of microparticles induced by torque was analyzed based on the Maxwell-Wagner polarization. Characteristic frequency corresponding to the peak value of the electrorotation speed was deduced and the effect of the relaxation time on the particles' electrorotation direction was analyzed by the simulation of the electrorotation speed induced by the torque. The mechanism of the electrorotation of the microparticles induced by electroosmotic slip was qualitative analyzed based on the double layer and the idea about the gold surface being favorable to the electrorotation was proposed. Experiments on the electrorotation of the polystyrene with the carboxy surface and gold modified surface were performed, respectively. The results show that, the direction of the electrorotation of polystyrene spheres with carboxy surface is opposite to the electric field and, the corresponding frequency is higher with the torque playing the leading role. On the other hand, direction of the rotation of polystyrene spheres with the gold surface is homodromous with the electric field and the corresponding frequency is lower with the electroosmotic slip playing the leading rose.