Spectroscopic monitoring of polymerization in microfluidic channels


Susan E. Barnes,* Zuzanna T. Cygan, Tao Wu, Jesse K. Yates and Kathryn L. Beers


Polymers Division, National Institute of Standards of Technology, Gaithersburg, MD 20899


There have been significant advances in the use of microfluidic devices for performing chemical analysis and reactions on the micrometer scale. Technology development in this field has been driven by the rewards gained from the use of microanalysis in replacement of its conventional macro-scale analogues. The small sample volumes associated with microfluidics demand application of sensitive analytical techniques for on-chip characterization of chemical species.

This study demonstrates the application of fiber optic Raman and near-infrared (NIR) spectroscopies as relatively inexpensive, portable techniques for characterization and monitoring of polymeric reactions inside microchannels. Results are presented from the application of Raman spectroscopy for combinatorial analysis of a gradient of methacrylate-based droplets formulated in a microfluidic device. Raman data have been acquired for accurate quantification of monomer composition in each droplet and degree of conversion of the particles following photopolymerization. Transmission NIR is demonstrated as a suitable technique for non-invasive, high-throughput measurement of the extent of monomer conversion as a function of reaction time.  NIR data are presented from analysis of the solution polymerization of n-butyl acrylate carried out in an integrated microchannel reactor. The results obtained are in agreement with those acquired from off-chip measurements of conversion acquired by NMR.

The results presented from both applications demonstrate that vibrational spectroscopic techniques are effective analytical tools for screening and quantitative analysis of polymeric materials on the micrometer scale in microfluidic devices.



Susan E Barnes

NIST Guest Researcher
National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg, MD 20899-8541, USA
Building 224, Room B226
Tel: (301) 975-6780
Fax: (301) 975-4924



Mentor: Kathryn L. Beers