Electrokinetic optimization of a micromixer for lab-on-chip applications

This paper is concerned with the optimization of an electrokinetic micromixer suitable for Lab-on-Chip and other microfluidic applications. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house Finite-Element-Method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e. frequency and amplitude, for a given waveform. The simulation results of two optimized electrical excitations featuring a discrete and a continuous waveform are compared and discussed. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly

Streaming potential revisited: the influence of convection on the surface conductivity

Electrokinetic phenomena play an important role in the electrical characterization of surfaces. In terms of planar or porous substrates, streaming potential and/or streaming current measurements can be used to determine the zeta potential of the substrates in contact with aqueous electrolytes. In this work, we perform electrical impedance spectroscopy measurements to infer the electrical resistance in a microchannel with the same conditions as for a streaming potential experiment. Novel correlations are derived to relate the streaming current and streaming potential to the Reynolds number of the channel flow. Our results not only quantify the influence of surface conductivity, and here especially the contribution of the stagnant layer, but also reveal that channel resistance and therefore zeta potential are influenced by the flow in the case of low ionic strengths. We conclude that convection can have a significant impact on the electrical double layer configuration which is reflected by changes in the surfaces conductivity

Streaming Potential Revisited: The Influence of Convection on the Surface Conductivity

Electrokinetic phenomena play an important role in the electrical characterization of surfaces. In terms of planar or porous substrates, streaming potential and/or streaming current measurements can be used to determine the zeta potential of the substrates in contact with aqueous electrolytes. In this work, we perform electrical impedance spectroscopy measurements to infer the electrical resistance in a microchannel with the same conditions as for a streaming potential experiment. Novel correlations are derived to relate the streaming current and streaming potential to the Reynolds number of the channel flow. Our results not only quantify the influence of surface conductivity, and here especially the contribution of the stagnant layer, but also reveal that channel resistance and therefore zeta potential are influenced by the flow in the case of low ionic strengths. We conclude that convection can have a significant impact on the electrical double layer configuration which is reflected by changes in the surfaces conductivity