Fundamentals of ATR Spectroscopy

The combination of infrared spectroscopy with the theories of reflection has made advances in surface analysis possible. Attenuated Total Reflectance (ATR) spectroscopy is an innovative technique for proving chemical information of a sample surface and the ability to quantify newly formed species, based upon Pick s second law. The fundamentals of attenuated total reflection (ATR) spectroscopy date back to the initial work of Jacques Fahrenfort and N.J. Harrick, both of whom independently devised the theories of ATR spectroscopy and suggested a wide range of applications. The schematic showing ATR-FTIR configuration is illustrated in Fig. 1 (KS. Kwan, 1998). The penetration depth, d, can be estimated as ... 

New directions have been recently advanced in the use of IR spectroscopy for the characterization of adsorbates, including the investigation of liquid-solid interfaces in situ during catalysis. Both ATR [91,92] and RAIRS [86,93] have been recently implemented for that purpose. RAIRS has also been used for the detection of intermediates on model surfaces in situ during catalytic reactions [94-96], The ability to detect monolayers in situ under catalytic environments on small-area samples promises to advance the fundamental understanding of surface catalytic reactions. 

To aid the general reader, short descriptions of the fundamentals of modern Raman scattering and attenuated total reflection (ATR) infrared spectroscopy are provided. This is followed for each spectroscopy by brief introductions to the enhancement mechanism involved. 

Because of the limitations in using mid-IR fibres, fundamental in-process spectroscopy will remain limited and dependent on special probes (ATR, transmission, etc.), near-IR and Raman are mid-IR rivals. The present development of NIR spectrometers offers several advantages compared to the mid-IR technique, e.g. faster measurements and easier sample treatment. It appears that in-process mid-IR spectroscopy is more geared towards reaction monitoring on the other hand, NIR spectroscopy plays a prime role for industrial on-line analysis (more general). 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

In an early study, Mauritz et al. investigated anion—cation interactions within Nation sulfonate membranes versus degree of hydration using FTIR/ ATR and solid state NMR (SSNMR) spectroscopies. An understanding of the dynamic ionic—hydrate molecular structures within and between the sulfonate clusters is essential for a fundamental understanding of the action of these membranes in ion transport. This information can be directly related to the equilibrium water swelling that, in turn, influences molecular migration. 

Fundamental for the characterization of polymer grafting surface are microscopy techniques, i.e. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Attenuated Total Reflection-Eourier transform infrared spectroscopy (ATR-FTIR spectroscopy). 

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