Raman spectroscopy in coatings research and analysis: Part I. Basic principles

In a previous article in the JCT COATINCSTECH Analytical Series, Chalmers discussed the use of infrared (IR) spectroscopy for characterizing and testing coatings. In this two-part companion article, we describe the use ofa complementary technique, Raman spectroscopy, for the same purposes. In common with Chalmers, we will not discuss the detailed principles of either small molecule or polymer characterization using Raman (or IR) spectroscopy; there are a large number of excellent review articles and textbooks which fulfill this purpose. Furthermore, we will not cover the basic aspects of Raman spectroscopy for the same reason. Rather, we concentrate on those aspects of Raman spectroscopy that are specific to coating science and technology, expanding on the fundamental principles only when necessary for clarity. Emphasis will be on organic coatings, but some attention will be paid to inorganics too. With this in mind, Part I of this tutorial attempts to address the following questions: What sort of information can be obtained using Raman spectroscopy? How is a coating studied in a typical Raman experiment? How thin for thick) of a coating can we study, and what is the influence of the substrate? After discussing these issues, Part II of this tutorial will focus on mapping or imaging chemical or structural variations in a coating. Examples, drawn both from the literature and the author's own work, will be used to illustrate the capabilities and limitations of the technique. This tutorial is not intended to be an exhaustive applications review, but hopefully it will indicate the wide variety of chemical and physical characterization problems that can be addressed.