Self-Assembly in the System Decanoic Acid–Butylamine–Water

Abstract

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 self-diffusion, 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 X-ray scattering results indicate that the amine, due to its slightly amphiphilic character, is distributed between water and the bilayer.