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MOLECULAR STRUCTURE AND FUNCTIONAL GROUP presence in organic paint and coating materials, typically, are determined using infrared spectroscopy. Evaluating the electronic structure of the binders such as the degree of conjugated double or triple bonds and degree of aromaticity may be evaluated using the more energetic ultraviolet (UV)/visible (VIS) spectroscopy. Dyes, some colorants, and aromatic solvents may be evaluated as well. UV/VIS radiation energizes the electrons within the molecule while infrared radiation causes physical movement of portions of the molecular structure. The use of electromagnetic radiation (EMR) for the analysis of paints and coatings is best addressed by looking at the way this energy source is absorbed by the system under investigation. Most EMR analytical techniques, and the instruments used to affect the measurement, will place the sample of known thickness in the beam of the “light.” The objective in this case is to determine the difference in the strength of the light beam before it enters the sample and the strength after emerging from the sample. This energy difference at a particular wavelength (energy) provides information about the absorbing species' concentration and/or chemical makeup. With some recent technology, the emerging beam may be reflected from a surface. There are many sophisticated instruments that use EMR, and they operate from the lowest energy bands in microwaves to the highest energy γ-rays. The region of the spectrum most commonly used in the paint laboratory lies within the infrared and UV bands. The instrumentation operative in this region can be relatively low cost, and the information that can be obtained about concentration and molecular structure, often, is very useful.
Mills, George D.
President, George Mills & Associates International, Inc., Foley, AL