Fourier transform infrared (FTIR) characterization of monolayers at the air-water interface.

摘要

The primary emphasis of chapter 2 is on the development of an optical model which is descriptive of the reflection-absorption properties from an anisotropic monolayer located on an isotropic liquid substrate. Relationships are established between the average chain orientation angle, anisotropic optical constants and the angle of incident light for s- and p-polarized radiation.; In chapter 3 a new method is developed for the simultaneous determination of chain orientation and surface concentration in monolayers on liquid substrates. The method is based on the use of s- and p-polarized reflection-absorption (RA) infrared intensities in conjunction with an optical model that includes anisotropy in the optical constants. Spectral simulations are given that address the issues of frequency shifting and band distortion in reflection-absorption due solely to optical considerations.; In chapter 4, monolayer films formed by aqueous solutions of sodium dodecane sulfonate (C{dollar}sb{lcub}12{rcub}{dollar}S) at the air-water interface have been studied by in situ reflection-absorption infrared spectroscopy. From both p- and s-polarized CH{dollar}sb2{dollar} stretching intensities, the chain orientation angles of the methylene tails of the C{dollar}sb{lcub}12{rcub}{dollar}S molecules on the aqueous substrates are calculated by using the methodology presented in chapter 3. The conformation of the alkyl chains of the C{dollar}sb{lcub}12{rcub}{dollar}S monolayers on aqueous substrates are determined by the CH{dollar}sb2{dollar} stretching peak positions. In addition to the CH{dollar}sb2{dollar} stretching mode, the SO stretching bands of the hydrophilic sulfonate group are also analyzed. The presence of phase transitions in monolayers are indicated by the alkyl chain conformational analyses and deviations from linearity in surface tension isotherms. The surface excess concentrations are calculated from both the infrared spectroscopic data and surface tension isotherms. Finally we discuss and model the effect of the gauche conformers on the chain orientation calculations.