Characterization of the phase behavior and complexation in the heptanoic acid-heptylamine-water system

The consequence of mixing an alkanoic acid with an alkylamine is a proton t ransfer between the acid and the amine leading to a complexation, which is dependent on the mixing ratio between the two components. If water is added , the formed ammonium alkanoate will have surfactant properties. In this wo rk the complexation between heptanoic acid and heptylamine in the presence of small amounts of water is investigated using C-13 NMR and FT-Raman techn iques. The results are compared with ab initio calculations, performed on t he propanoic acid-propylamine system. Several water-containing complexes ar e considered. The added water does not interfere with the complexation obse rved experimentally in the absence of water. Instead it breaks the acid dim ers, forming acid monomer-water complexes. Furthermore the lamellar liquid crystalline phase formed in the heptanoic acid-heptylamine-water system was characterized using SAXS. The swelling behavior at an equimolecular ratio between the acid and the amine deviates from that for other binary amine ma ss fractions.