arXiv:1002.4444v1 [cond-mat.soft] 24 Feb 2010 Extensional Instability in Electro-Osmotic Microflows of Polymer Solutions R.M. Bryce ∗ and M.R. Freeman † Department of Physics, University of Alberta, Edmonton T6G 2G7, Canada. National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton T6G 2M9, Canada. (Dated: November 21, 2018) Fluid transport in microfluidic systems typically is laminar due to the low Reynolds number characteristic of the flow. The inclusion of suspended polymers imparts elasticity to fluids, allowing instabilities to be excited when substantial polymer stretching occurs. For high molecular weight polymer chains we find that flow velocities achievable by standard electro-osmotic pumping are sufficient to excite extensional instabilities in dilute polymer solutions. We observe a dependence in measured fluctuations on polymer concentration which plateaus at a threshold corresponding to the onset of significant molecular crowding in macromolecular solutions; plateauing occurs well below the overlap concentration. Our results show that electro-osmotic flows of complex fluids are disturbed from the steady regime, suggesting potential for enhanced mixing and requiring care in modeling the flow of complex liquids such as biopolymer suspensions. PACS numbers: 47.20.Gv,47.57.Ng,47.57.jd,47.61.-k $^{∗}$Electronic address: rbryce@phys.ualberta.ca $^{†}$Electronic address: mark.freeman@ualberta.ca 1 Abstract