Drag reduction in electro-osmosis of polymer solutions

Electro-osmosis is the preferred transport mechanism in microfluidic systems. Drag reduction in electro-osmosis of polymer solutions is observed due to polymer depletion in the electric double layer (EDL). The well-known Helmholtz-Smoluchowski (HS) equation indicates that the electro-osmosis mobility is inversely proportional to the solution viscosity. For low molecular weight the polymer size (R) is smaller than the EDL thickness (lambda) and the HS equation is valid. For high molecular weight (R>lambda) the chains in the EDL are partially sheared and the effective viscosity is smaller than the solution viscosity. Salt addition reduces lambda and can enhance drag reduction substantially. (C) 2007 American Institute of Physics.