Investigations of Radical Polymerization and Copolymerization Reactions in Optically Levitated Microdroplets by Simultaneous Raman Spectroscopy, Mie Scattering, and Radiation Pressure Measurements

Abstract

The combination of the optical levitation technique with Raman spectroscopy, elastic (Mie) scattering, and radiation pressure measurements enables in situ and real-time investigation of polymerization and copolymerization processes in single microdroplets. The time-dependent evolution of the polymerization and copolymerization reactions of styrene/unsaturated polyester resin (UP-resin) is characterized by observing the educt and product signals in the Raman spectra. The size, the refractive index, and the wavelength dependence of the refractive index of the optically levitated microparticle are determined from the position of the morphology-dependent resonances observed in Raman spectra, in elastic light scattering, and in radiation pressure measurements. This additional information about droplet properties as a function of time allows a better understanding of the entire reaction process within the microdroplet.