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Abstract Recent studies have demonstrated the strong influences of fluid rheological properties on insulator‐based dielectrophoresis (iDEP) in single‐constriction microchannels. However, it is yet to be understood how iDEP in non‐Newtonian fluids depends on the geometry of insulating structures. We report in this work an experimental study of fluid rheological effects on streaming DEP in a post‐array microchannel that presents multiple contractions and expansions. The iDEP focusing and trapping of particles in a viscoelastic polyethylene oxide solution are comparable to those in a Newtonian buffer, which is consistent with the observations in a single‐constriction microchannel. Similarly, the insignificant iDEP effects in a shear‐thinning xanthan gum solution also agree with those in the single‐constriction channel except that gel‐like structures are observed to only form in the post‐array microchannel under large DC electric fields. In contrast, the iDEP effects in both viscoelastic and shear‐thinning polyacrylamide solution are significantly weaker than in the single‐constriction channel. Moreover, instabilities occur in the electroosmotic flow and appear to be only dependent on the DC electric field. These phenomena may be associated with the dynamics of polymers as they are electrokinetically advected around and through the posts. 

Abstract Insulator‐based dielectrophoretic (iDEP) microdevices have been limited to work with Newtonian fluids. We report an experimental study of the fluid rheological effects on iDEP focusing and trapping of polystyrene particles in polyethylene oxide, xanthan gum, and polyacrylamide solutions through a constricted microchannel. Particle focusing and trapping in the mildly viscoelastic polyethylene oxide solution are slightly weaker than in the Newtonian buffer. They are, however, significantly improved in the strongly viscoelastic and shear thinning polyacrylamide solution. These observed particle focusing behaviors exhibit a similar trend with respect to electric field, consistent with a revised theoretical analysis for iDEP focusing in non‐Newtonian fluids. No apparent focusing of particles is achieved in the xanthan gum solution, though the iDEP trapping can take place under a much larger electric field than the other fluids. This is attributed to the strong shear thinning‐induced influences on both the electroosmotic flow and electrokinetic/dielectrophoretic motions.