Joule heating effects on electroosmotic flow in insulator-based dielectrophoresisInsulator-based dielectrophoresis (iDEP) is an emerging technology that has been successfully used to manipulate a variety of particles in microfluidic devices. However, due to the locally amplified electric field around the in-channel insulator, Joule heating often becomes an unavoidable issue that may disturb the electroosmotic flow and affect the particle motion. This work presents the first experimental study of Joule heating effects on electroosmotic flow in a typical iDEP device, e.g. a constriction microchannel, under DC-biased AC voltages. A numerical model is also developed to simulate the observed flow pattern by solving the coupled electric, energy, and fluid equations in a simplified two-dimensional geometry. It is observed that depending on the magnitude of the DC voltage, a pair of counter-rotating fluid circulations can occur at either the downstream end alone or each end of the channel constriction. Moreover, the pair at the downstream end appears larger in size than that at the upstream end due to DC electroosmotic flow. These fluid circulations, which are reasonably simulated by the numerical model, form as a result of the action of the electric field on Joule heatinginduced fluid inhomogeneities in the constriction region.

Joule heating (JH) is a ubiquitous phenomenon in electrokinetic microfluidic devices. Its effects on fluid and ionic species transport in capillary and microchip electrophoresis have been well studied. However, JH effects on the electrokinetic motion of microparticles in microchannels have been nearly unexplored in the literature. This paper presents an experimental investigation of JH effects on electrokinetic particle transport and manipulation in constriction microchannels under both pure dc and dc-biased ac electric fields. It is found that the JH effects reduce the dielectrophoretic focusing and trapping of particles, especially significant when dc-biased ac electric fields are used. These results are expected to provide a useful guidance for future designs of electrokinetic particle handling microdevices that will avoid JH effects or take advantage of them.