(366g) Mapping AC Electroosmotic Flow At the Dielectrophoresis Crossover Frequency of a Colloidal Probe

The AC electroosmosis (ACEO) flow field in the vicinity of conducting electrodes is mapped by the measurement of Stokes-Einstein forces on an optically trapped colloidal particle. Dielectrophoresis (DEP) of the probe particle is eliminated by measuring at the particle’s DEP crossover frequency. At this frequency the DEP force on the particle vanishes. Isolation of ACEO from DEP of the probe utilizes the fact that the ACEO flow velocity depends strongly on the electric field, which is spatially dependent, whereas the DEP crossover frequency, is independent of the electric field. Elimination of the particle’s DEP permits unambiguous mapping of the ACEO velocity field.