ENHANCED ELECTROKINETIC MICROMIXING BY OPTIMAL PATTERNING OF HETEROGENEOUS SURFACE CHARGE

摘要

Microfluidic devices require efficient micromixing for fast analysis in biological applications such as enzyme assays, biochemical reaction and detection etc. (Chang 2006, Atalay et al. 2009). In a conventional T - mixer design, where two confluent streams mix due to transverse diffusion, longer channel lengths and times are required to achieve complete mixing. The micromixing performance can be significantly enhanced by non-axial flows generated by geometric/ surface modification of microchannel (Nguyen and Wu 2005). For electrokinetic micromixers (Chang and Yang 2007), the mixing performance can be enhanced significantly by addition of heterogeneous surface charge on sidewalls and/or bottom of the microchannel. The non-uniform surface potential/ charge produce localized flow circulations in electroosmotic flow fields (Ajdari 1995, Stroock and Whitesides 2003). Previous studies have shown that the induced non-axial flow structure due to presence of heterogeneity augment micromixing performance (Biddiss et al. 2004, Chang and Yang 2006). However, the effect of heterogeneous charge patterns on mixing performance is not systematically studied. In this computational study, we investigate the effect of heterogeneous charge patterns at the microchannel bottom on the mixing performance. A binary numerical optimization problem is formulated to achieve best mixing performance by identifying the optimal heterogeneous charge pattern. The details of optimization and mathematical model are presented in the next section.