The effects of electroosmosis (EO) and electrophoresis (EP) interactions on the movement of highly charged polystyrene microspheres and lesser-charged liposome nanoparticles were studied, using a microscale cross-slot flow device with different charge density and polarity on the channel surfaces. When the particle EP mobility is greater than the channel surface EO mobility, the flow pattern would be either extensional or extension dominated mixed-shear. The rotation flow only exists when the EO mobility dominates. The surface charge density of top and bottom lids of microchannels plays an important role in microfluidics. Experimental observations agreed fairly well with calculated flow patterns.
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