Fluid rheological effects on dielectrophoretic focusing and trapping of particles in a constricted microchannel

Microfluidic devices have been extensively used for particle focusing and trapping in chemical and biomedical applications in recent years. Insulator-based dielectrophoresis (iDEP) is an emerging technique that controls particles via dielectrophoresis induced by the strong electric field gradients around insulating structures. However, studies on particle manipulation in iDEP microdevices have been limited to Newtonian fluids. This work reports an experimental study of the individual and combined effects of fluid elasticity and shear thinning on particle manipulation through a constricted microchannel. Five types of non-Newtonian fluids with distinct rheological properties are tested, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), hyaluronic acid (HA) and polyacrylamide (PAA) solutions. The dielectrophoretic force is of purely electric origin, and hence should be independent of the fluid rheology. However, the observed particle focusing and trapping phenomena are significant different among the prepared non-Newtonian fluids though they are all dilute polymer solutions in the same electrolyte buffer.