Application of micromixers - Micromixers Fundamentals Design and Fabrication - page 330

FIGURE 9.4
Schematic concepts of micromixer applications in chemical analysis: (a) NMR measurement; (b) CE
measurement; and (c) freeze-quenching reactions.

biochemical reactions. The freeze-quenching technique ejects the mixed solution from a continuous-
flow mixer through a small nozzle into an isopentane bath at a low temperature (-130 C). The frozen
samples contain trapped reaction intermediates that can be conveniently investigated without the time
constraints ( Fig. 9.4 (c)). On a macroscale, the application of freeze-quenching technique is limited
because of the long mixing time and the slow freezing time of cryogenic fluids. The delay time is
generally on the order of milliseconds. Before the spectroscopic investigation, the reaction should be
initiated in a way such that all of the molecules are in phase. A mixer should work as a microreactor for
this purpose. The earliest time allowed by conventional mixers for detection of the intermediates is on
the order of milliseconds. Although the time limit can be solved by lowering the reaction temperature
and fast spectroscopic tools, it is easier to reduce the mixing dead time using micromixers. The
micromixer reported by Lin et al. [46] allows freeze quenching within 20 s resulting in ultrafine frozen

m

powder with excellent spectral quality and high packing factor.