Dielectrophoresis of submicrometer latex spheres. 1. Experimental results

A nonuniform electric field exerts a force on a polarizable particle through the Coulomb interaction with the electric dipole induced in the particle, resulting in a motion termed dielectrophoresis. The magnitude of the force depends on the dielectric properties of both the particle and the medium it is suspended in. As a result, measurement of the dielectrophoretic force provides information about the internal and surface dielectric properties of the particle. This paper presents the first detailed measurements of the dielectrophoretic response of submicrometer particles as a function of electrolyte composition and conductivity, applied field frequency, and particle size. Comparisons are made between the experimental results and the classical theory of the dielectrophoretic force derived from Maxwell-Wagner interfacial polarization. For particles of 557 nm diameter, good agreement is obtained between the experimental results and theory of interfacial polarization taking into account the effects of surface conductance. However, the results for smaller sizes of particle (93, 216, and 282 nm diameter) demonstrate that the theory does not adequately explain the dielectric or dielectrophoretic behavior of colloidal particles. The existence of a second low-frequency dispersion is also apparent in the data, attributable to the polarization of the double layer. The data were compared with a theoretical plot generated by modeling the dispersion in terms of a single Debye relaxation.