Theory of dielectrophoresis in colloidal suspensions

A theoretical study of the dielectrophoretic (DEP) spectrum of a pair of touching colloidal particles or biological cells in a host fluid under the application of a nonuniform alternating current (ac) electric field is presented. The main objective of this work is to investigate the correlation effects due to the presence of mutual polarization on the DEP spectrum. In particular, we employ the multiple image method to account for the effect of multiple images, and obtain an analytic expression for the DEP force. It is found that, at low frequencies, the DEP force can be enhanced (reduced) significantly for the longitudinal (transverse) field case due to the presence of multiple images. The numerical results can be well understood in the spectral representation theory. To first order in the dipole interaction, our results reduce to the established formula derived by an alternative method. Our approach demonstrates the importance of the correlation effects in ac electrokinetic phenomena of colloidal suspensions. (C) 2004 American Institute of Physics.