Mesophase State of Amphoteric Surfactants of β-alanine Type and Their Temperature Dependence of ¹H-NMR and IR Spectra

Abstract

The condition of liquid crystal appearance for amphoteric surfactant molecules of N-dodecyl-β-alanine substituted by hydroxy groups was examined by the temperature dependence of ¹H-NMR and IR spectra. The half line-width of an active proton signal does not decrease in the liquid crystal state and the inter-molecular hydrogen bond between hydroxy groups attached to the 2-nd carbon atom in the dodecyl group begins to be broken just below the melting point. From these results, a liquid crystal model was proposed as following: a rod-like dimer is formed by a pair of strong hydrogen bonds NH⁺ ₂—⁻O₂C between two molecules and the parallel orientation of these rod-like units are maintained by another type of hydrogen bonds between hydroxy group at the 2-nd carbon atom in dodecyl group on both sides of the central structure composed of NH⁺ ₂—⁻O₂C hydrogen bonds. In addition, the information about the class of primary or secondary alcohols and the location of hydroxy groups was obtained by the analysis of time dependence of NMR spectra in the solvent of trifluoroacetic acid.