Time-dependence of local boundary conditions and global throughput for confined, semi-dilute polymer solutions*

Confined polymer solution flows are often found, for example, in biological systems and porous media. In such systems, for which the surface to volume ratio is high, interfacial effect are key. Specifically, the flow throughput is highly impacted by boundary effects such as slip or chain adsorption at the wall, and these latter interfacial effects may be time-dependent. In this study, we use evanescent wave microscopy and particle tracking velocimetry to map the flow field within a one-micron layer close to the wall in a 5-micron-thick microfluidic chip. While this technique has been shown very efficient to characterize the near-wall shear rate and hydrodynamic boundary condition, we additionally use state-of-the-art flow sensors to measure the flow rate and pressure drop across the chip simultaneously. Live monitoring of the local flow profile and global flow rate allows a description of the adsorption dynamics of hydrolyzed polyacrylamide chains onto a glass surface, under shear flow. The dependence in the shear rate, chain concentration and electrolyte concentration is studied.