Comparison of the FT-IR mapping and imaging techniques applied to polymeric systems

Two Fourier transform infrared (FT-IR) spectrometers with microspectroscopi c capabilities-one equipped with a focal plane array (FPA) mercury-cadmium- telluride (MCT) detector (imaging) and the other a single-element MCT detec tor (mapping)-are compared, Two samples, a one-dimensional diffusion system and a two-dimensional phase-separated system, were studied with both analy tical tools. Diffusion regions and concentration gradients were determined in the diffusion sample. Phase-specific chemical composition data were obta ined in the phase-separated sample. The utility of each instrument for spec ific cases and their respective limitations are illustrated. It is shown th at the FPA system has the ability to sample a large sample area with high s patial resolution in a short time without adverse diffraction effects. Beca use of this very rapid sampling many dynamic processes can he studied which are otherwise poorly monitored by the point-by-point mapping technique. Th e spatial resolution achievable, the quality of data obtained [signal-to-no ise ratio (SNR)], and temporal resolution between mapped areas are intimate ly connected in the mapping system. However, the imaging systems have a fix ed spatial resolution (dependent on the optics and detector) and the SNR co nsiderations 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 curren t FPA technology. The chemical information obtained from both instruments i s, within a small experimental error, identical. This work demonstrates wha t can be accomplished with each analytical FT-IR instrument, and serves as a comparative study to demonstrate the value of each analytical tool in spe cific situations.