Electro-osmotic characteristics of Polystyrene microchips – Experiments and modeling

Electro-osmotic characteristics such as the electro-osmotic velocity, the electro-osmotic mobility and zeta-potential were determined in polystyrene microfluidic chips by the conductivity (electric current monitoring) method. The capillary microchips were fabricated with the use of micromilling and hot assembling techniques. A linear dependence of the electro-osmotic velocity on the voltage applied on 39 mm long microcapillaries was obtained. The electro-osmotic mobility and zeta-potential were found to be equal to 2.26 ± 0.12 × 10−8 m2 V−1 s−1 and −29.0 ± 1.5 mV, respectively.The conductivity method is based on the electro-osmotic replacement of two electrolytes with different electric conductivities under a constant voltage. This fact leads to a non-linear distribution of the electric field intensity along the capillary. We developed two dynamical mathematical models describing the conductivity method. It was found that the formation of complex velocity fields and significant gradients of pressure and the electric field intensity accompanies this method. It finally results in a non-linear time response of electric current.