Reflection-absorption FT-IR spectroscopy of vinyl octadecanoate at the air/water interface

Reflection-absorption Fourier transform infrared (RA FT-IR) spectra of spre ad monolayers of vinyl octadecanoate have been obtained for a range of surf ace pressures at 292 K. Unpolarised and s- and p-polarised radiation at 30 degrees angle of incidence have been used. Results in the C-H stretching re gion show that even at very low surface pressures the monolayer appears to consist of condensed domains where the acyl chains are highly ordered and d ensely packed. At higher surface pressures the average packing density is h igher, but otherwise the spectra are unaltered, showing that the acyl chain s remain highly ordered with few gauche bonds throughout the accessible ran ge of surface pressure (0.1 to 18 mN m(-1)). There was no appreciable chang e in the spectrum when the monolayer passed through the LC to S phase trans ition. (C) 1999 Elsevier Science B.V. All rights reserved.