title: Raman spectroscopic monitoring of droplet polymerization in a microfluidic device.
abstract: Microfluidic methodologies are becoming increasingly important for rapid formulation and screening of materials, and development of analytical tools for multiple sample screening is a critical step in achieving a combinatorial 'lab on a chip' approach. This work demonstrates the application of Raman spectroscopy for analysis of monomer composition and degree of conversion of methacrylate-based droplets in a microfluidic device. Droplet formation was conducted by flow focusing on the devices, and a gradient of component composition was created by varying the flow rates of the droplet-phase fluids into the microchannels. Raman data were collected using a fiber optic probe from a stationary array of the droplets/particles on the device, followed by partial least squares (PLS) calibration of the first derivative (1600 cm(-1) to 1550 cm(-1)) allowing successful measurement of monomer composition with a standard error of calibration (SEC) of +/-1.95% by volume. Following photopolymerization, the percentage of double bond conversion of the individual particles was calculated from the depletion of the normalized intensity of the C[double bond, length as m-dash]C stretching vibration at 1605 cm(-1). Raman data allowed accurate measurement of the decrease in double bond conversion as a function of increasing crosslinker concentration. The results from the research demonstrate that Raman spectroscopy is an effective, on-chip analytical tool for screening polymeric materials on the micrometre scale.
authors.affiliation: NIST Combinatorial Methods Center, Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20879-8542, USA.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Barnes
authors.forename: Zuzanna T
authors.initials: ZT
authors.lastname: Cygan
authors.forename: Jesse K
authors.initials: JK
authors.lastname: Yates
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Beers
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Amis