By a comparison of infrared reflection-absorption (RA) and transmission intensities, a method for the quantitative evaluation of molecular orientation in thin Langmuir-Blodgett (LB) films has been developed. The enhancement factors for the RA to transmission absorption intensities of hypothetical isotropic films were theoretically calculated by using Hansen's optical formulas for thin multilayer films. By combination of these values with the experimentally determined intensity ratios of the RA to transmission spectra for uniaxially oriented LB films, the orientation angles of the transition moments of major infrared bands were evaluated. Application of this method to the 7-monolayer LB film of cadmium stearate deposited on Ag (for RA measurements) and on ZnSe (for transmission measurements) substrates gave reasonable tilt angles for the molecular chain as compared to those reported by other investigators and to the data from the X-ray analysis. This method will be discussed in detail and the various factors which influence the accuracy of the orientation analysis will also be covered.

Fourier transform infrared (FTIR)-attenuated total reflection (ATR) spectra have been recorded of Langmuir-Blodgett (LB) films of stearic acid deposited on a germanium plate with 1, 2, 3, 5, and 9 monolayers. Examination of the CH2 scissoring band suggests that the hydrocarbon chain of stearic acid in the first monolayer is in a hexagonal or pseudohexagonal subcell packing where each hydrocarbon chain is freely rotated around its axis oriented approximately perpendicular to the surface. In the LB films thicker than 2 monolayers, on the other hand, the molecules in the upper monolayers other than the first monolayer crystallize with the monoclinic form where the hydrocarbon chains are packed alternately and are inclined at an angle of about 30°with respect to the surface normal, showing a tendency to align their a crystal axes parallel to the direction of the withdrawal of the germanium plate in the film preparation. It is also concluded from frequencies and intensities of the progression bands due to the CH2 wagging vibrations that stearic acid occurs as the cis configuration for the C=0 and Ca-€ß bonds in the 1-monolayer film but the trans configuration starts to appear in the 3-monolayer film. A striking feature in this study is the absence of the C-O stretching band of stearic acid in the first monolayer on the germanium plate. This phenomenon may be interpreted by the short-range image field model for its oscillating dipole parallel to the germanium surface.

adsorption solutions. All the buffers were 0.05 M, with the exception of the pH 11 buffer, which was 0.1 M. The following buffers were used for the titrations under cyclooctane:malonic acid (pH = 2, 3), sodium phosphate (4, 12), acetic acid (5), maleic acid (6), HEPES (7, 8), boric acid (9,10) l,3-diamino-2propanol (11), and KC1 (13). The pH of the buffers was within 0.1 unit of the values stated.Acknowledgment. We thank S. R. Holmes-Farley and Ernest B. Troughton (Lord Corporation) and H. Biebuyck for valuable discussions during the course of this work.

No abstract