Chain length effect on the structure and thermotropic phase transitions of solid catanionic complexes built of cetyltrimethylammonium bromide and saturated n-fatty acids

Abstract

Chain length effect on the structure and thermotropic properties of asymmetric solid catanionic complexes (CAC) built of cetyltrimethylammonium bromide (C16TABr) and saturated n-fatty acids (CnSFA, CnH2nO2, n = 12, 18, 20, and 22) was investigated by XRD, DSC, and FTIR spectroscopy. All CAC show a lamellar crystalline structure and a series of solid–solid phase transitions below the melting point. The phase transitions are suggested to be caused by sequential melting of the methylene chains in the hydrophobic layer followed by a change in the crystalline structure. C16TABr stabilizes the bilayer structure of CAC and raises its melting point compared to initial CnSFA.