Chapter 3 - Diffusion and mixing in microfluidic devices

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Many pharmaceutical and biological applications require a controlled mixing of multiple samples in microfluidic devices. Because of the small length scale of the microchannels, the flow is always in the laminar regime; the dominant mechanism of mixing is thus diffusion and/or chaotic laminar mixing. Depending on the requirement of the mixing speed, some applications use diffusion as the sole mechanism, such as microfluidic gradient generators, while other applications make use of both diffusion and chaotic mixing to implement a fast and thorough blending of multiple constituents, such as microfluidic mixers. This chapter provides a brief review of the controlled mixing in microfluidic devices, from the fundamentals of fluid dynamics and mass transfer to the design principles and application examples of microfluidic gradient generators and mixers. Specifically, we will include the following contents.