A Three-Dimensional Flow Focusing Microsecond Mixer for Dynamic Assessment of Nanoparticle Formation

This paper reports the design, fabrication, and characterization of a three-dimensional flow focusing microfluidic mixer. By hydrodynamically focusing the sample stream into a very confined jet in both vertical and horizontal directions, the mixer can achieve ultrafast mixing of reagents within ~3 ± 1 μs. Such rapid mixing allows us to dynamically assess the formation of nanomaterial and study their assembly kinetics on microsecond timescale. Using the mixer, we investigated the formation of the hexaphenylsilole (HPS) nanoparticles. Compared to those formed by bulk nanoprecipitation, the HPS nanoparticles formed in the mixer have smaller size with narrower size distribution. We also kinetically resolved that the microsecond molecular self-assembly of HPS molecules displays two distinct steps. These results suggest that the formation of HPS nanoparticles follows the classical nucleation and growth theory.