In this work, a new Fourier transform infrared spectroscopic technique (diffuse transmittance) is introduced. Its principle is based on the collection and the analysis of the diffusely transmitted infrared radiation through fibrous samples. The qualitative as well as the quantitative aspects of the method have been investigated. A comparative analysis of diffuse reflectance (DRIFT) and diffuse transmittance (DT) spectra shows that orientation of the sample has little effect on DT spectra, as compared with DRIFT spectra. With the use of ultra-high modulus polyethylene fabrics as a substrate coated with 12-nitrododecanoic acid, the concentration dependence of F(T), a function of the diffuse transmittance T, defined as F(T) = (1 - T)2/2T, was investigated within the coating thickness range of 0 to 50 nm.
A. Taboudoucht and H. Ishida, "Diffuse Transmittance Spectroscopy of Polymeric Fibers," Appl. Spectrosc. 43, 1016-1021 (1989)