Chemical Characteristics of Sea Slicks and Oil Spills - Marine Surface Films - page 22

Fig. 7. IR reflection-absorption spectra for a PME slick at the air/water interface
after compression to 0.272 nm 2 /molecule and subsequent relaxation, from bottom
to top after 10, 30, 50, and 80 min, respectively
versa , accessible to water molecules during dilation of the film. The same
hydration effect can also be observed during the increasing ordering of the
film molecules, i.e., a higher order means more space per molecule and
thus an increased possibility for a hydration of the head group. This phe-
nomenon can be followed by IRRAS: In the spectra shown in Fig. 7, a
strong band is observed at 1739 cm -1 directly after spreading and also 10
min thereafter. This band represents the C=O vibration of an unhydrated
carbonyl group. In the course of the relaxation procedure (Fig. 7, t ! 10
min), a second band appears at 1720 cm -1 which indicates the C=O vibra-
tion of a hydrated carbonyl group. This results shows that alkanoic acid es-
ters, which are often being found in biogenic sea slicks, are continuously
hydrated and dehydrated during compression and dilation on an undulating
water wave field. It can be safely assumed that the strong wave damping
effect of these compounds is centrally related to this phenomenon.
With the aim of simulating biogenic sea slicks, we generated PME
slicks at the sea surface by distributing the film-forming material with the
help of different spreading solvents, i.e., by the application of ethanol or n -
hexane. These man-made sea slicks were overflown by a helicopter carry-