Web Release Date: September 21,
High-Temperature Microfluidic Synthesis of CdSe Nanocrystals in Nanoliter Droplets
and
Contribution from the Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
Received March 4, 2005
Abstract:
The high-temperature synthesis of CdSe nanocrystals in nanoliter-volume droplets flowing in a
perfluorinated carrier fluid through a microfabricated reactor is presented. A flow-focusing nanojet structure
with a step increase in channel height reproducibly generated octadecene droplets in Fomblin Y 06/6
perfluorinated polyether at capillary numbers up to 0.81 and with a droplet:carrier fluid viscosity ratio of
0.035. Cadmium and selenium precursors flowing in octadecene droplets through a high-temperature (240-300 
C) glass microreactor produced high-quality CdSe nanocrystals, as verified by optical spectroscopy
and transmission electron microscopy. Isolating the reaction solution in droplets prevented particle deposition
and hydrodynamic dispersion, allowing the reproducible synthesis of nanocrystals at three different
temperatures and four different residence times in the span of 4 h. Our synthesis of a wide range of
nanocrystals at high temperatures, high capillary numbers, and low viscosity ratio illustrates the general
utility of droplet-based microfluidic reactors to encapsulate nanoliter volumes of organic or aqueous solutions
and to precisely control chemical or biochemical reactions.
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