5. Chemically treated surfaces of polystyrene

A final example in this topic deals with infrared analysis of chemically-altered surfaces of polystyrene spheres which are approximately 0.5 mm in diameter. Both FTIR-PAS and DRIFTS spectra are plotted in Fig. 30. The DRIFTS spectrum shows very expanded weak absorbance bands, inverted or derivatized strong bands, and some absent bands. The FTIR-PAS spectra measured at an OPD mirror velocity of 0.5 cm/s show both polystyrene bands and bands due to the chemical treatment. In this instance, it was not possible to isolate the chemically-treated layer from the underlying polystyrene. Consequently, spectral subtraction using a spectrum of untreated polystyrene was necessary in order to isolate the absorbance bands due to the chemical treatment.

Fig. 30. FTIR spectra of polystyrene spheres with and without chemically-treated surfaces. In this case, the very deep-sampling depth of DRIFTS results in grossly distorted spectra. FTIR-PAS allows the spectrum due to the chemical surface treatment to be observed after spectral subtraction. The samples were provided by Prof. R.A. Kellner of the Institute of Analytical Chemistry, Technical University of Vienna.

E. Carbon-Filled Materials

Materials with significant concentrations of carbon in fiber or powder form are highly opaque and consequently are difficult to analyze by infrared spectroscopy. These materials, however, are of considerable industrial importance and their infrared spectra provide very useful information for research and development and for production operations.
Baseline slope is often present in spectra of very strongly absorbing samples. It is magnified by the need to expand the ordinate scale of spectra to a high degree in order to see absorbance bands above a strong background absorption due, for instance, to carbon black.