Mid Sweden University

The phase behavior of alkanoic acid-alkylamine mixtures in water is mainly dictated by a proton transfer from the acid to the amine. For an asymmetric distribution of carbon atoms in the alkyl chains, the result will be an ionic surfactant with an organic counter-ion. In this study the phase diagram at 298.2 K for the ternary system decanoic acid-butylamine-water has been determined. The phase diagram is dominated by a large isotropic solution region. The selfdiffusion, viscosity, and conductivity measurements in the solution phase for an equimolecular ratio between the acid and the amine indicate a continuous transition from aqueous spherical mixed micelles to highly interacting hydrated acid-amine complexes passing through a bicontinuous region. One liquid crystalline lamellar phase, existing at excess acid, has been found. The small angle Xray scattering results indicate that the amine, due to its slightly amphiphilic character, is distributed between water and the bilayer.