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Monolayers of hexadecyltrimethylammonium p-tosylate at the air-water interface. 1. Sum-frequency spectroscopy

1998

Article

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Sum-frequency vibrational spectroscopy has been used to determine the structure of monolayers of the cationic surfactant, hexadecyltrimethylammonium p-tosylate (C(16)TA(+)Ts(-)), at the surface of water. Selective deuteration of the cation or the anion allowed the separate detection of sum-frequency spectra of the surfactant and of counterions that are bound to the monolayer. The p-tosylate ions an oriented with their methyl groups pointing away from the aqueous subphase and with the C-2 axis tilted, on average, by 30-40 degrees from the surface normal. The vibrational spectra of C(16)TA(+) indicate that the number of gauche defects in the monolayer does not change dramatically when bromide counterions are replaced by p-tosylate. The ends of the hydrocarbon chains of C16TA+ are, however, tilted much further from the surface normal in the presence of p-tosylate than in the presence of bromide. A quantitative analysis of the sum-frequency spectra requires a knowledge of the molecular hyperpolarizability tensor: the role of ab initio calculations and Raman spectroscopy in determining the components of this tensor is discussed.

Author(s): Bell, GR and Li, ZX and Bain, CD and Fischer, Peer and Duffy, DC
Journal: JOURNAL OF PHYSICAL CHEMISTRY B
Volume: 102
Number (issue): 47
Pages: 9461-9472
Year: 1998

Department(s): Micro, Nano, and Molecular Systems
Bibtex Type: Article (article)

DOI: 10.1021/jp982142+

BibTex

@article{ISI:000078514100015,
  title = {Monolayers of hexadecyltrimethylammonium p-tosylate at the air-water interface. 1. Sum-frequency spectroscopy},
  author = {Bell, GR and Li, ZX and Bain, CD and Fischer, Peer and Duffy, DC},
  journal = {JOURNAL OF PHYSICAL CHEMISTRY B},
  volume = {102},
  number = {47},
  pages = {9461-9472},
  year = {1998}
}