Lyotropic liquid crystal behaviour of azelate and succinate monoester surfactants based on fragrance alcohols

Azelaic acid was used as a starting material for the preparation of new monoester surfactants based on fragrance alcohols. Sodium monocitronellyl azelate (citroC 9Na) and sodium monomenthyl azelate (menC 9Na) were synthesized and their aqueous phase behaviour was studied. For comparison, monoesters derived from succinic anhydride, i.e. sodium monocitronellyl succinate (citroC 4Na) and sodium monomenthyl succinate (menC 4Na), were also prepared as well as sodium monodecyl succinate (C 10C 4Na) and sodium monodecyl azelate (C 10C 9Na) in order to study the effect of the position of the ester function inside the hydrophobic tail and of branching and unsaturation respectively. Liquid crystal structures were examined by optical polarising microscopy and schematic partial binary phase diagrams (surfactant + water, 0–100 wt%, 10–90 °C) of the surfactants were established. Succinate surfactants behave as longer alkyl chain surfactants than their azelate counterparts, meaning that these last ones probably adopt a more folded conformation, with the ester function more frequently present at the micelle surface. This conformation would result in a rougher micelle surface, making it slightly less easy for micelles to pack in liquid crystalline phases. It was also shown that the tendency to adopt a more folded conformation and to form smaller micelles is ranked in this order: monomenthyl > monocitronellyl > monodecyl.