Double-layer polarization of a non-conducting particle in an alternating current field with applications to dielectrophoresis.

Dielectrophoresis is becoming one of the most important techniques in particle manipulation including particle separation, particle assembly, and biomolecule characterization. Understanding dielectrophoretic properties of particles is a key step toward effective and efficient particle manipulation. Theoretical studies of polarization of a particle can help to understand experimental observations and also go beyond to develop a predictive theory to guide the experimental design. This article discusses recent theoretical advances in the polarization of a dielectric particle, in particular, the polarization of the electric double layer. The double-layer polarization is critical to determine particle dynamics in dielectrophoresis. The dipole moment characterizing the strength of this polarization depends on the double-layer thickness, the electric field frequency, the particle's surface charge, and other surface's properties (Pohl, H. A., Dielectrophoresis, Cambridge University Press, New York 1978). After a brief review of the mathematical model, the focus is on the following problems: (i) the polarization of a spherical particle; (ii) the polarization of an elongated cylindrical particle; (iii) the effect of the slip on the polarization of a particle. The double-layer polarization is examined here in the context of high-frequency and low-frequency dispersions induced by surface conduction and diffusion, respectively.