Reaction-driven solvent transport in UV-curable phase-separating coatings

We experimentally examined the time-evolutions of local compositions in photocurable, monomer-solvent-initiator ternary liquid film coatings using attenuated total-reflectance-Fourier transform infrared spectroscopy. The coatings exhibited phase separation upon UV exposure owing to the inherent partial miscibility between the solvent and the polymer. The solvent concentration at the bottom of the coating increased when exposed to UV light for 1 s from the top, showing a solvent transport along the irradiation direction. The differences in solvent concentration before and after UV exposure showed good agreement with model predictions based on stress-induced non-Fickian solvent mass transport. The solvent concentrations at the bottom remained constant in the case of discrete phase structures, whereas it exponentially decayed over time in bicontinuous phase structures. These results suggest that light-tunable microstructures enable the relaxation of the reaction-driven nonuniformity in solvent concentration distributions.