MOLECULAR-ORIENTATION OF A CYANOBIPHENYL LIQUID-CRYSTAL IN FREELY SUSPENDED FILMS AND AT THE AIR-WATER-INTERFACE

Langmuir films and freely suspended (FS) films of 4'-n-octyl-4-cyanobi phenyl (8CB) in the smectic A phase have been studied by Fourier trans form infrared spectroscopy. Examination of FS film transmission spectr a gives a good estimation of molecular group orientation in the uniaxi al him. At the air-water interface 8CB shows a first-order phase trans ition from a monolayer to a trilayer when the surface pressure increas es. We have studied such films using polarisation modulated infrared r eflection absorption spectroscopy. Specific surface selection rules on dielectrics allow an estimation of the orientation of the cyanobiphen yl core in the monolayer and in the trilayer and comparison of molecul ar organisations in the two types of films.