Abstract
Sum-frequency (SF) spectroscopy and ellipsometry have been used to study monolayers of the cationic surfactants CnTAB (CH3(CH2)n-1N+(CH3)3Br-) (n = 12, 14, 16, and 18) at the air-water interface at a constant surface area of 44 Å2/molecule. The SF spectra of all four surfactants are very similar and yield a mean chain tilt of 58° near the methyl terminus. The ellipsometric data suggest that the density of the chain region in the monolayers is close to that of a liquid hydrocarbon, which is consistent with the chain tilt derived from the sum-frequency spectra. These results are in quantitative agreement with detailed structural profiles of C12TAB and C16TAB determined by Thomas and co-workers by neutron reflection.
Published Version
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