POLARIZATION MODULATION IRRAS INVESTIGATION OF A CELLULOSE ETHER AT THE AIR WATER INTERFACE/

Spread monolayers of a cellulose alkyl ether (HPC-C16) have been inves tigated at the air/water interface by polarisation modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Infrared spectra exhib it bands associated with the symmetric and anti-symmetric methylene st retching vibrations, as well as with the methylene scissoring vibratio n, at 2850, 2917 and 1471-1463 cm(-1), respectively. Air of these band s appear as positive peaks in the PM-IRRAS spectra, indicating that th e hexadecane sidechains have a net orientation perpendicular to water surface. The relatively low frequencies of the methylene stretching ba nds suggest that the hydrocarbon sidechains adopt a near all-trans con formation. The intensity of these bands increases with decreasing mole cular area during monolayer compression. This increase is due not only to an increase in the surface density of the absorbing groups but als o to orientational changes. These results indicate that alkyl sidechai n orientation at the air/water interface is, to a certain degree, depe ndent on the surface pressure. Furthermore, no change in orientation i s observed during compression through the plateau typically present in surface pressure-area isotherms of these polymers. (C) 1998 Elsevier Science S.A. All rights reserved.