Effect of lecithin on organogel formation of 12‐hydroxystearic acid

Optically active 12‐d‐hydroxystearic acid (12‐HSA) gives a thermally reversible organogel in several organic solvents. When a small amount of lecithin coexists with 12‐HSA in organic solvents, the mechanical strength of the organogel is remarkably reduced. Interaction of lecithin with 12‐HSA was studied by using infrared (IR) spectrometry, nuclear magnetic resonance (NMR) spectrometry, and scanning electron microscopy (SEM). Incorporating lecithin into 12‐HSA reduced the absorbance in IR spectra, derived from hydrogen bonding between the hydroxyl groups and the carboxyl groups of 12‐HSA molecules. Based on NMR measurements, the polar head groups of lecithin associate with the carboxyl groups of 12‐HSA in a 1:1 molar ratio. SEM showed that the shape of the fibrous aggregates varied from a helically extended form to a spherical form. These results suggest that intermolecular 1:1 complexes were formed between lecithin and 12‐HSA, which caused a structural change in the fibrous network in the 12‐HSA organogel and consequently induced gel deformation.