High flow rate per power electroosmotic pumping using low ion density solvents

Abstract

We present experimental investigations of electroosmotic pumping using porous borosilicate glass and various low ion density liquids. The working liquids were deionized water, deuterium oxide (heavy water), methanol, acetone, acetonitrile and a 1 mM sodium borate buffer as a control. We measured ionic conductivity and, as a useful comparative reference, the zeta potential generated by these liquids in borosilicate microfluidic chips. We evaluated the electroosmotic pump performance of porous borosilicate glass structures in terms of flow rate, pressure and total ionic current. We compared experimental data to an analytical model based on numerical solutions of nonlinear Poisson–Boltzmann equation. In particular, we extend the model to the pumping of pure solvents and found a reasonable agreement with experimental results. For negligible pressure loads, pump flow rate per applied electric power can be more than ten times higher with acetone than with the 1 mM sodium borate buffer. For finite pressure loads, methanol typically yields the highest flow rate per applied electric power due to its higher pressure capacity compared to acetone. Low ion density liquids also showed strong current transients. At present, we do not have a clear understanding of the physics behind these transients, but we present measurements of current startup and discuss possible explanations for the data.