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.

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The observation of a phase transition from a solid microparticle into a liquid droplet of a single levitated NH 4 NO 3 particle using an electrodynamic balance for particle levitation combined with Raman and Mie spectrospcopy is reported. The phase transition from the solid to the dissolved NH 4 NO 3 can be followed by characteristic changes in the spectral location of Raman signals and by a characteristic decrease in the refractive index and an increase in the particle radius, which is deduced from Mie scattering data. Copyright

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