Ac electrokinetics is a versatile technique for particle and fluid manipulation in microfluidic environment. However, analyzing and predicting particle motions due to the ac electrokinetic effects is a difficult task because it requires the quantitative understanding of multiple phenomena such as dielectrophoresis (DEP), ac electroosmosis (ACEO), and electrothermal effects (ETE). In this paper we present a force balance approach to analyze ac electrokinetic effects, particularly ACEO. Pressure-driven flows were used to quantify the ACEO and DEP forces acting on a particle. Polystyrene microbeads suspended in KCl solution were introduced in polydimethylsiloxane (PDMS) microchannels attached to a glass plate with gold microelectrodes. The microbeads were initially collected and aligned along the center of the electrodes at 1 kHz and 1 Vp-p, and then a well-controlled pressure-driven flow was introduced resulting in the translation of the particles. Particles moved to a new location where a new force balance is reached. This particle translation on the surface of the electrode was carefully monitored as varying the applied flow rate. The net force due to ac electrokinetic effects at different locations over the electrode was calculated using the experimental data and the force balance relationship.

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