EVALUATION OF MOLECULAR-ORIENTATION IN A POLYMERIC MONOLAYER AT THE AIR-WATER-INTERFACE BY POLARIZATION-MODULATED INFRARED-SPECTROSCOPY

Polarization-modulated reflection - absorption spectroscopy (PM-IRRAS) is employed to record infrared spectra of. monolayer of (dodecyl)cell ulose spread at the air-water interface. Methylene symmetric and antis ymmetric stretches of the alkyl side chains are clearly visible in the monolayer spectra as positive peaks at 2852 and 2922 cm(-1). It is th us concluded that the side chains possess a net orientation perpendicu lar to the water surface. Bands characteristic of the cellulose backbo ne are also observed as positive PM-IRRAS peaks, in the region 1160-98 0 cm(-1). This result indicates that the rigid polysaccharide chain li es essentially parallel to the water surface. Spectra recorded as a fu nction of molecular area reveal little change in molecular orientation during monolayer compression. Significant differences in orientation are however evident between dense films obtained by the compression of disperse monolayers and those prepared by direct spreading at low sur face areas.