The Application of Linear PA/FT-IR to Polymer-Related Problems

Abstract

A simplified method has been developed which allows the computation of linear photoacoustic FT-IR spectra using only one sample and one reference interferogram from a commercial, rapid-scan spectrometer. The application of linear computation to photoacoustic infrared data can produce spectra similar to transmission spectra through the reduction, if not elimination, of the saturation artifacts typical of amplitude computation, the usual mode of producing a PA/FT-IR spectrum or a transmission mode spectrum. Comparison of the resulting linear spectra with amplitude spectra has been used to demonstrate the existence of surface layers on top of substrates. Qualitative identification of the surface layer is easier in this mode than in the case where amplitude spectra are obtainted at the extremes of instrument mirror velocity. Additionally, information concerning a polymer matrix in the presence of up to 25 wt % carbon black is contained in linear photoacoustic spectra. Linear photoacoustic FT-IR spectra of carbon-filled samples are easier to interpret in comparison to spectra obtained by amplitude methods.