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Advances in Physical Chemistry
Volume 2012 (2012), Article ID 903272, 14 pages
http://dx.doi.org/10.1155/2012/903272
Research Article

Infrared Spectroscopy of Anionic, Cationic, and Zwitterionic Surfactants

1Departamento de Química e Física Molecular, Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos, SP, Brazil
2Departamento de Química, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, RJ, Brazil

Received 21 January 2012; Revised 7 April 2012; Accepted 8 April 2012

Academic Editor: Michael D. Sevilla

Copyright © 2012 Rommel B. Viana et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This paper describes the ordering degree of anionic, cationic, and zwitterionic surfactants with the increase of their packing density on Ge substrate by using Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy. This work shows new insights on the conformational order of sodium dodecyl sulfate (SDS), N-hexadecyl-N-N-dimethyl-3-ammonio-1-propane-sulfonate (HPS), hexadecyl-trimethylammonium bromide (CTAB), and dodecyl trimethylammonium bromide (DTAB). DFT and semiempirical calculations are also performed in order to evaluate the effect of headgroup hydration and counterion. The CH2 asymmetric and symmetric stretching bands for the SDS molecule show a shift of 1.7 and 0.9 cm−1 to higher frequencies as the packing density increases, while it is observed a shift of 2.6 and 2.7 cm−1 for the HPS molecule, respectively. The DTAB molecule shows a shift of 4.5 cm−1 to lower frequencies for both CH2 asymmetric and symmetric stretching bands as the packing density increases, indicating the decrease of gauche conformations and the increase of all-trans conformations over the aliphatic chain.