Characterization of Photocurable Coatings Using Fluorescence Probes

摘要

In this paper, we describe a novel method for monitoring the degree of cure and coating thickness of photocurable resins using intramolecular charge transfer (ICT) fluorescence probes such as 5-dimethylaminona phthalene-1-sulfonyl-n-butylamide (DASB) and 6-propionyl-2-(dimeth ylamino)-naphthalene (PRODAN). As the curing reaction proceeded, the fluorescence emission spectra of the ICT probes were found to exhibit hypsochromic spectral shifts because of the increase in matrix microviscosity, which made it more difficult for the excited molecule to relax to its twisted charge transfer state. The spectral changes of the probes as a function of the degree of the cure were monitored using a fluorescence intensity ratio method, which enabled an internal calibration of fluctuations in lamp intensity and sample thickness. It was found that the ratios of the fluorescence emission intensities at two different wavelengths were correlated linearly with the degree of polymerization for different types of acrylic or unsaturated polyester resins using either UV or visible (VIS) initiators. The coating thickness of photopolymers was measured based upon the nascent fluorescence from the coating substrate by virtue of an emission (from the substrate) and absorption (by the coating) mechanism. The thicker the coating, the less the nascent fluorescence emission that can be observed. So the intensity of the nascent fluorescence from the substrate can be correlated to the coating thickness. jg p2.