Dielectrophoretic Behavior of Polystyrene Particles Under Direct Current and Low Frequency Electric Fields

Dielectrophoresis (DEP) is the movement of particles due to polarization effect when particles are exposed to non-uniform electric field. In insulator based dielectrophoresis (iDEP), non-uniform electric fields are generating by employing arrays of insulating structures. The Clausius-Mossotti (CM) factor is the parameter that accounts for particle polarization and it can be positive or negative, the CM factor dictates the direction of the dielectrophoretic force, which can be positive or negative. Positive DEP (pDEP) is when particles are attracted to the regions of higher electric field gradient, and negative DEP (nDEP) is particle repulsion from those regions. When the Clausius-Mossotti (CM) factor for polystyrene particles is plotted as a function of electric field frequency, high frequencies correspond to negative CM factors and negative dielectrophoresis (nDEP) while low and mid-range frequencies correspond to positive CM factors and positive dielectrophoresis (pDEP). However, iDEP experiments with direct current (DC) electric fields generally result in nDEP even when the particles are supposed to have positive CM factors. This work is focused on characterization the behavior of polystyrene particles of different sizes, including sub-micron level, under DC and low frequency alternating current (AC) electric fields. Modeling with COMSOL Multiphysics was used to theoretically predict the distribution of the electric field in microchannel with insulating posts. Experiments were performed in devices made from polydimethylsiloxane (PDMS) through soft lithography techniques. The results will provide a deeper understanding of dielectrophoretic particle behavior in the conductivity regime.