Bio-based castor oil organogels and investigations on their anion-tuning properties

Abstract

We report here bio-based N-(2-hydroxyethyl) ricinoleic amide (NHRA) a derivative of castor oil, as a low molecular weight gelator showing good gelation in organic solvents. NHRA gelator molecules exhibited thermoreversible gelation in specific tested organic solvents such as aniline and 1,4 dioxane. The gelator molecules are self-assembled through intermolecular hydrogen bonding and van der Waals interactions which are the determining factors for the organogel formation as confirmed by FT-IR spectroscopy. Differential scanning calorimetry (DSC) measurements show the phase transition of gels from gel to solution state and strongly depend by varying the concentration of the gelator. The supramolecular aggregation of gelators in the gel state led to viscoelastic nature of the organogels and was studied by rheology. Morphological studies reveal the presence of lamellar fibrous-like structures, which are responsible for the molecules to aggregate into 3D network. The synthesized organogel acts as a host for anions that change the physical state from gel to sol by disruption of intermolecular hydrogen-bonding interactions. The propensity of the material to exhibit anion-responsive behavior is attributed to the presence of amide linkages, under which deprotonation of N–H fragments occur upon the addition of anions, as confirmed by 19F NMR and FT-IR spectroscopy. These results indicate that NHRA gelator can be prospective candidate for sensing applications