Further Developments in the Methodology of Surface Analysis by FT-IR: Quantitative Aspects of Diffuse Reflectance Methods

Abstract

The quantitative aspects of diffuse reflectance FT-IR are explored for standard E-glass/AAPS ( N-2-aminoethyl-3-aminopropyltrimethoxysilane) treated samples. Nondestructive sample preparation procedures are used. One generates calibration curves by plotting the normalized integrated intensity of the coupling agent bands in the 2990–2800 and 1700–1500 cm−1 regions vs. the concentration of the treatment solution. The data are derived by DRIFT spectroscopy, and the above results are plotted for the overlayer technique as well as for no overlayer. The scatter in the quantitative data due to fiber orientation effects has been measured and is found to be significant (20–30%). However, averaging over several orientations of the fibers results in a linear dependence of the integrated intensities of the coupling agent bands on solution concentration. The well-known breakpoint that has been observed for other coupling agent systems does not appear in the curve derived from the averaged spectra. The above-mentioned scatter is eliminated by the use of KBr overlayers on the samples. Linear calibration curves relating band intensity to concentration can be constructed. When the overlayer procedure is used, breakpoints do occur in the calibration curves. The position of these breakpoints agrees well with observations for the similar coupling agent γ-APS.