Infrared Spectroscopy of Anionic, Cationic, and Zwitterionic Surfactants

[摘要] 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 CH2asymmetric and symmetric stretching bands for the SDS molecule show a shift of 1.7 and 0.9 cm−1to higher frequencies as the packing density increases, while it is observed a shift of 2.6 and 2.7 cm−1for the HPS molecule, respectively. The DTAB molecule shows a shift of 4.5 cm−1to lower frequencies for both CH2asymmetric and symmetric stretching bands as the packing density increases, indicating the decrease ofgaucheconformations and the increase of all-transconformations over the aliphatic chain.

[学科分类] 物理化学和理论化学