Raman Spectroscopic Monitoring of Droplet Polymerization in a Microfluidic Device
Susan E. Barnes, Zuzanna T. Cygan, Kathryn Beers, Eric J. Amis, Jesse K. Yates
Thiolene based microfluidic devices were used to generate droplets of benzyl methacrylate monomer and hexanediol dimethacrylate crosslinker mixtures suspended in a water/surfactant continuous phase. A gradient of droplet composition was established and the ensemble of droplets was collected on the device. On-chip Raman spectroscopy was used to verify a composition gradient from 18 to 98 volume % benzyl methacrylate. The droplets were then exposed to UV light to initiate polymerization and subsequent Raman spectra were taken to determine extent of conversion.Conversion was found to vary with composition across the gradient with 78% conversion at low benzyl methacrylate concentrations to 95% at high benzyl methacrylate concentrations. Image analyses of micrographs taken before and after polymerization were used to measure shrinkage due to polymerization. Shrinkage values ranged from 4% to 12% and increased with increasing benzyl methacrylate concentration.