Comparison of the FT-IR Mapping and Imaging Techniques Applied to Polymeric Systems

Abstract

Two Fourier transform infrared (FT-IR) spectrometers with microspectroscopic capabilities—one equipped with a focal plane array (FPA) mercury-cadmium-telluride (MCT) detector (imaging) and the other a single-element MCT detector (mapping)—are compared. Two samples, a one-dimensional diffusion system and a two-dimensional phase-separated system, were studied with both analytical tools. Diffusion regions and concentration gradients were determined in the diffusion sample. Phase-specific chemical composition data were obtained in the phase-separated sample. The utility of each instrument for specific cases and their respective limitations are illustrated. It is shown that the FPA system has the ability to sample a large sample area with high spatial resolution in a short time without adverse diffraction effects. Because of this very rapid sampling, many dynamic processes can be studied which are otherwise poorly monitored by the point-by-point mapping technique. The spatial resolution achievable, the quality of data obtained [signal-to-noise ratio (SNR)], and temporal resolution between mapped areas are intimately connected in the mapping system. However, the imaging systems have a fixed spatial resolution (dependent on the optics and detector) and the SNR considerations determine temporal resolution. However, it was also shown that by aperturing to a localized region, the single-element detector system is able to arrive at phase concentration information more rapidly, with less cumbersome processing and with higher SNRs than is possible with the current FPA technology. The chemical information obtained from both instruments is, within a small experimental error, identical. This work demonstrates what can be accomplished with each analytical FT-IR instrument, and serves as a comparative study to demonstrate the value of each analytical tool in specific situations.