FOURIER-TRANSFORM INFRARED METAL OVERLAYER ATTENUATED TOTAL REFLECTION SPECTRA OF LANGMUIR-BLODGETT-FILMS OF 12-HYDROXYSTEARIC ACID AND ITS CADMIUM SALT

dl-12-Hydroxystearic acid (12HSA) exhibits a wide plateau region in its surface pressure-area isotherm. LB films of 12HSA were prepared at various stages of surface compression on silver-coated slide glasses. FTIR metal overlayer ATR spectra of these LB films were recorded and intensity ratios of the symmetric CH3 stretching band to the symmetric CH2 stretching band were analyzed as well as frequencies of the latter band, The results indicate that the average orientation of the methylene chains toward the surface normal upon compression is improved slightly in the plateau region, but greatly at the solid-condensed state. The cadmium salt of 12HSA which has no plateau region showed higher perpendicular orientation even at very low surface pressure.