Theory of Electrorotation of Clustered Colloidal Particles

When a colloidal suspension is exposed to a strong rotating electric field, an aggregation of the suspended particles is induced to appear.In such clusters, the separation between the suspended particles is soclose that one could not neglect the multiple image effect on theelectrorotation (ER) spectrum. Since so far the exact multiple imagemethod exists in two dimensions only, rather than in three dimensions,we investigate the ER spectrum of the clustered colloidal particles intwo dimensions, in which many cylindrical particles are randomly distributed in a sheet cluster. We report the dependence of the ER spectrum on the material parameters.It is shown that the multiple image method predicts twocharacteristic frequencies, at which the rotation speed reachesmaximum. To this end, the multiple image method is numericallydemonstrated to be in good agreement with the known Maxwell-Garnett approximation.