Microreactor Fluidics DOI: 10.1002/ange.200500792 A Microfabricated Gas–Liquid Segmented Flow Reactor for High-Temperature Synthesis: The Case of CdSe Quantum Dots** BrianK.H. Yen, Axel Günther, MartinA. Schmidt, Klavs F. Jensen,* and MoungiG. Bawendi* Microfluidic reactors enable a number of advantages over conventional chemical processes including enhanced control of heat and mass transfer, lower reagent consumption during optimization, and sensor integration for in-situ reaction monitoring. [1, 2] Reactors are usually fabricated from either silicon, glass, or polymers; those made of silicon or glass are advantageous because they can tolerate a broad range of chemistries and high temperatures. Microreactors for the large class of homogeneous liquid-phase reactions are often based on single-phase laminar flow designs in which reagent streams are brought into contact. However, such designs are limited in terms of slow diffusive reagent mixing and broad residence time distributions (RTDs). Recirculation within segments in a two-phase segmented flow approach (gas– liquid or liquid–liquid) overcomes such limitations by provid- ing a mechanism of exchanging fluid elements located near the channel walls with those at the center. [3–5] This recircula- tory motion has the dual effect of narrowing the RTD and improving reactant mixing. In contrast to single-phase designs, segmentation makes it possible to drive reactions to required yields over significantly shorter times owing to the enhanced mixing, while maintaining narrow RTDs. [*] A. Günther, Prof. K. F. Jensen Massachusetts Institute of Technology Department of Chemical Engineering Institute for Soldier Nanotechnologies 77 Massachusetts Avenue, 66–566, Cambridge, MA 02139 (USA) Fax: (+ 1) 617-258-8224 E-mail: kfjensen@mit.edu B. K. H. Yen, Prof. M. G. Bawendi Massachusetts Institute of Technology Department of Chemistry Institute for Soldier Nanotechnologies 77 Massachusetts Avenue, 6–221, Cambridge, MA 02139 (USA) Fax: (+ 1) 617-253-7030 E-mail: mgb@mit.edu Prof. M. A. Schmidt Massachusetts Institute of Technology Microsystems Technology Laboratories Department of Electrical Engineering and Computer Science Cambridge, MA 02139 (USA) [**] This research was funded in part by the NSF-CRC program (CHE- 0209898), the Microchemical Systems Technology Center, and the U.S. Army through the Institute for Soldier Nanotechnologies (under contract DAAD-19-02-0002 with the U.S. Army Research Office). B.K.H.Y. acknowledges support from the NDSEG Fellow- ship Program. We thank the staff of the MIT Microsystems Technology Laboratories for assistance with microfabrication. Angewandte Chemie 5583 Angew. Chem. 2005, 117, 5583 –5587 # 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim