Double-Layer AC Tangential Conduction Effects on Polarization, Assembly and Dielectrophoretic Mobility of Particles in Ionic Liquids

Polarization of gas bubbles and liqud drops by an AC field in ionic liquids is shown to exhibit anomalous induced-dipole behaviors that cannot be explained by classical Maxwell-Wagner dielectric polarization theories. A dielectrophoretic cross-over frequency exists even though the ionic liquid has much higher permittivity and conductivity than the particle, even when conducting Stern layer effects are included. Moreover, the cross-over frequency is observed to be field and particle size dependent. Drops of different size can hence have anti-parallel induced dipoles and are observed to coalesce at an intermediate frequency between the cross-over frequencies of the two particles. ~A scaling theory based on a thin-layer tangential conduction model is found to collapse our measured cross-over frequency and dielectrophoretic velocity data.