Effect of Chain Length on the Structure of Monolayers of Alkyltrimethylammonium Bromides (C n TABs) at the Air−Water Interface

Sum-frequency (SF) spectroscopy and ellipsometry have been used to study monolayers of the cationic surfactants C n TAB (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...

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Bibliographic Details
Published in:The journal of physical chemistry. B 1998-01, Vol.102 (1), p.218-222
Main Authors: Bell, Graham R, Manning-Benson, Samantha, Bain, Colin D
Format: Article
Language:English
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Summary:Sum-frequency (SF) spectroscopy and ellipsometry have been used to study monolayers of the cationic surfactants C n TAB (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.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp972647k