Theory of Electrode Polarization in Dielectrophoresis and Electrorotation

Experimental observations, previously reported in the low frequency regime of the spectrum in dielectrophoresis and electrorotation of plant protoplasts, have revealed serious discrepancies between the predictions of the "Shelled Model" and measurements. Much work has also been carried out in the theoretical realm to reconcile these discrepancies by introducing such mechanisms as charge flow on the surface of the cell and micromotion, but in all this the effects of electrode polarization have been neglected. Part of the problem lies in the rather formidable nature of the analysis that must be carried out with nonuniform fields since the entire system of governing partial differential equations must be considered. In the case of uniform fields it is convenient to formulate the problem in the language of ordinary differential equations. This problem is further exacerbated by the lack of a well defined boundary condition at the outer limit of the double layer. We have used the method of Green's functions, since this allows the consideration of partial differential equations in a more natural way than the other methods, in order to formulate the problem. The lack of a well defined boundary condition at the outer surface is dealt with by taking an integral transform of the governing equations and thus recovering a relationship between the applied and the far fields. The results of our analysis show that the double layer relaxation, in the selected model, is a very simple single relaxation process and its effect is to diminish the discrepancies between theory and experiment. Copyright 1997 Academic Press. Copyright 1997Academic Press