Assessment of Micromixer Design in Microfluidic Chips via Mixing Efficiency Measurement Using Contactless...

The performance of microfluidic reactors is fundamentally determined by the structural optimization of internal mixing channels, which directly influences reaction rates and product uniformity. Traditional evaluation methods, including fluorescence imaging and CFD simulations, frequently encounter semiquantitative limitations, are prone to interference, or rely on idealized assumptions. Herein, we developed a quantitative evaluation platform founded on Capacitively Coupled Contactless Conductivity Detection (C⁴D) for the precise benchmarking of microfluidic mixer designs. Using wrap-around electrodes, the platform measures the cross-sectional average mixing state at multiple locations along the microchannel, thereby eliminating errors associated with focal plane selection in optical methods. With instantaneous acid-base neutralization as a standardized model, the mixing process is decoupled from reaction kinetics, ensuring measured signals accurately reflect the structural performance of the micromixer. Evaluations across various geometries demonstrate that periodic convergent-divergent sections generate a "stretching-folding" flow field, overcoming diffusion limitations and yielding a mixing index above 90% within 0.24 s. This work provides a robust, direct methodology for the quantitative assessment and rational structural design of high-performance microreactors.