Theory of Electrorotation of Clustered Colloidal Particles

When a colloidal suspension is exposed to a strong rotating electric field, an aggregation of the suspendedparticles is induced to appear. In such clusters, the separation between the suspended particles is so close that one couldnot neglect the multiple image effect on the electrorotation (ER) spectrurm. Since so far the exact multiple image methodexists in two dimensions only, rather than in three dimensions, we investigate the ER spectrum of the clustered colloidalparticles in two dimensions, in which many cylindrical particles are randomly distributed in a sheet cluster. We reportthe dependence of the ER spectrum on the material parameters. It is shown that the multiple image method predictstwo characteristic frequencies, at which the rotation speed reaches maximum. To this end, the multiple image methodis numerically demonstrated to be in good agreement with the known Maxwell Garnett approximation.