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 CH 2 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 CH 2 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.
Viana, R. B., da Silva, A. B. F., & Pimentel, A. S. (2012). Infrared Spectroscopy of Anionic, Cationic, and Zwitterionic Surfactants. Advances in Physical Chemistry, 2012, 1–14. https://doi.org/10.1155/2012/903272