Abstract
Small-scale mixing is of uttermost importance in bio- and chemical analyses using micro TAS (total analysis systems) or lab-on-chips. Many microfluidic applications involve chemical reactions where, most often, the fluid diffusivity is very low so that without the help of chaotic advection the reaction time can be extremely long. In this article, we will review various kinds of mixers developed for use in microfluidic devices. Our review starts by defining the terminology necessary to understand the fundamental concept of mixing and by introducing quantities for evaluating the mixing performance, such as mixing index and residence time. In particular, we will review the concept of chaotic advection and the mathematical terms, Poincare section and Lyapunov exponent. Since these concepts are developed from nonlinear dynamical systems, they should play important roles in devising microfluidic devices with enhanced mixing performance. Following, we review the various designs of mixers that are employed in applications. We will classify the designs in terms of the driving forces, including mechanical, electrical and magnetic forces, used to control fluid flow upon mixing. The advantages and disadvantages of each design will also be addressed. Finally, we will briefly touch on the expected future development regarding mixer design and related issues for the further enhancement of mixing performance.
Highlights
In microfluidic applications, mixing has been understood as one of the most fundamental and difficult-to-achieve issues
During the last five years, since two nice review papers [1,2] were published in 2005 on microfluidic mixing, several hundreds of papers have been published on this topic
We review the various ideas of the microfluidic mixers reported since 2005
Summary
In microfluidic applications, mixing has been understood as one of the most fundamental and difficult-to-achieve issues. In this review paper we summarize the skeletons of the ideas behind the proposed designs and address the advantages as well as the disadvantages of each design for use in practical applications. Falk and Commenge [4] addressed use of the method of performance comparison or evaluation of micromixers by using the Villermaux/Dushman reaction They combined the order-ofmagnitude analysis and a phenomenological model to derive relation between the mixing time and other parameters such as the Reynolds number. No review paper has been found which addresses key features of various types of micro mixers and evaluates them in terms of their mixing performance, versatility of application and difficulty of fabrication, etc. This review paper summarizes the fundamental ideas behind the mixer designs presented in the papers published in 2005 and thereafter, as well as the application range and the fabrication difficulty of these.
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