Study on the concentration profiles in phase-separating photocuring coatings
Scientists directly measured the local composition profiles in phase-separating photocurable thin films using confocal Raman spectroscopy.
To avoid light scattering at phase interfaces, they developed a novel technique to replace the solvent with a monomer to match the reflective indices in the cured films. The results indicated that the concentration distribution of the polymer was uniform in solvent-free monomer/initiator binary solutions, while it was spatially nonuniform when the solvent-based films were thermodynamically unstable and promoted reaction-induced phase separation upon UV irradiation on the top surface.
Dual-layer structure
In the latter case, the film exhibited a dual-layer structure, in which the polymer concentration was almost uniform near the top surface, while concentration gradients developed near the bottom surface. The thickness of the top layer with a uniform concentration profile increased with the increase in the UV light intensity.
These results implied that the propagation of the reaction front and the resulting light-driven transport of the solvent toward the bottom coating layer played key roles in the formation of nonuniform concentration profiles in photocuring solution coatings.
The study has been published in Journal of Coatings Technology and Research, Volume 16, 1629–1636.
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