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 io
nic 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 re
gion. The selfdiffusion, viscosity, and conductivity measurements in the so
lution phase for an equimolecular ratio between the acid and the amine indi
cate a continuous transition from aqueous spherical mixed micelles to highl
y 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 amin
e, due to its slightly amphiphilic character, is distributed between water
and the bilayer. (C) 2001 Academic Press.