Double-layer effects on low frequency dielectrophoresis-induced colloidal assembly

Strong frequency dependence of particle aggregation in applied ac-electric fields is reported for colloidal assembly under positive dielectrophoresis. A curious low-frequency threshold omega(th) on the order of 10(4)-10(5) Hz is observed for the onset of collecting submicron latex particles at the high-field regions near coplanar electrodes. Similar to the dielectrophoretic crossover frequency, omega(th) is independent of medium conductivity, sigma(m) at low-salt concentration, yet scales with sigma(0.5)(m) at high-salt concentrations. This intriguing salt effect suggests the distinct contribution from Stern and diffuse layer conductance to the interfacial polarization mechanism of latex particles in nonuniform ac fields. (c) 2008 American Institute of Physics.