Infrared Spectroscopy in the Analysis, Characterization, and Testing of Coatings

JCT CoatingsTech In this JCT COATINGSTECH series of introductory tutorial articles, the emphasis sought is on the applications of modern analytical, characterization, and testing methods for coatings. And while it is easy to cite many examples of recent applications of mid-infrared spectroscopy, the most common sampling techniques employed have been well established for a long time and, as a consequence, mid-infrared spectroscopy has been at the forefront of analytical methods for characterizing coatings and surfaces for many years. In 1980, the Federation of Societies for Coatings Technology (FSCT) published an Infrared Spectroscopy Atlas for the Coatings Industry,1 which contained over 1400 mid-infrared spectra, covering categories such as polymers, monomers, solvents, inorganic pigments and extenders, organic pigments, and various additives. A fourth edition of Infrared Spectroscopy Atlas for the Coatings Industry, which contains ca. 2500 mid-infrared spectra, was published in two volumes by the FSCT in 1991.2 In addition to its established position as a favored technique for characterizing and analyzing polymers,3-6 the long tradition for using mid-infrared spectroscopy to study and characterize in situ coatings stems essentially from two sampling technique developments in the 1960s. The first, known as ATR (Attenuated Total Reflection) mid-infrared spectroscopy, is an internal reflection spectroscopy technique.7-11 The second, more specialized technique is an external reflection approach undertaken at grazing angle of incidence, which is often referred to as RAIRS (Reflection-Absorption Infrared Spectroscopy),12 or some other similar acronym. Mid-infrared ATR spec-