Electro-osmotic flow of electrolyte solutions of PEO in microfluidic channels

We investigate if the shear-stress exerted on the wall of a glass microchannel can be a robust and accurate criterion for the safe electro-osmotic transfer of polyethylene oxide (PEO) chains dissolved in a NaCl aquatic solvent. To this end, a comprehensive multiscale formulation based on the rheological and electrochemical modeling of the PEO dynamics is proposed. Phenomena that occur in microscale, e.g., the migration of PEO to the core region of the channel and Polymeric Depletion Layer (PDL) formation, and in nanoscale, e.g., the development of an electric double layer on the glass surface and ionic steric effects, are included.

We study the electro-osmotic flow of PEO solutions (0.1-0.5%), flowing in a glass microchannel of rectangle shape, with dimensions of 300 μm in length and 75 μm in height. We vary the externally applied electric field (300-500 V/cm), and the bulk ionic concentration (0.001-10 mM).

We find that all features of our formulation are indeed essential to reproduce the experimental data of Huang, Chen, Wong, Liow, Soft Matter, (2016) precisely. Although the PDL formation preserves the fragile nature of biopolymers, the dominant stress is the normal stress, and the critical value is at the PDL interface. A new design criterion for microdevices is proposed.