Abstract
A novel microfluidic mixer based on periodically varying the ζ-potential on the microchannel walls through the field-effect control and asymmetric-herringbone electrode design has been developed and demonstrated successfully. In contrast to previous micromixer work from other groups, this micromixer does not need complex three-dimensional serpentine microstructure or external pumps to generate chaos-like flow. The influences of parameters such as pH value, ionic concentrations of the electrolyte, and radial electric field on the ζ-potential are discussed in thesis. They indicate that it is easier to modulate ζ-potential on the microchannel wall in the condition of a lower pH value and lower concentration of the buffer solution. The mathematical models for the influence of the nonuniform ζ-potential on the velocity profile, the volumetric flow rate, and the induced pressure distribution in a rectangular cross-section microchannel are also derived and show the mixing effect of varying ζ-potential. Numerical simulation results utilizing CFDRC show the good mixing efficiency for our micromixer design with asymmetric herringbone electrodes and periodic voltage control. The microfabrication process for our electrokinetic micromixer has been developed successfully. Via the quantitative analysis of Image Processing Toolbox in Matlab, experimental results successfully demonstrate a great mixing enhancement compared with diffusion effect only Our electrokinetic micromixer design can enhance the mixing effect by appropriate modulation of the ζ-potential, which results in manipulating local flow fields. The work reported here considers for the first time temporal/spatial ζ-potential modulation for microfluidic mixer applications.