Self-assembly in vegetable oils of ionic gelators derived from (R)-12-hydroxystearic acid

Abstract

Abstract We investigated the self-assembly mechanism of N -alkyl-( R )-12-hydroxyoctadecylammonium chlorides ( n -HOA-Cl; n = 3, 4, 6, and 18) during the development of organogels (5 wt%) in safflower oil. The n -HOA-Cl are ionic gelators derived from the 12-hydroxystearic acid, some capable of forming both hydro- and organo-gels (i.e., ambidextrous). The results showed that self-assembly of the n -HOA-Cl resulted from a balance between electrostatic and London dispersion forces. During cooling the n -HOA-Cl self-assembled, initially, through electrostatic interactions between the protonated nitrogen atoms and the chloride counter ions of molecule pairs giving rise to an exotherm (T Cr1 ). Further cooling resulted in a second exotherm (T Cr2 ) associated with the crystallization of the n- alkyl chains. After achieving 10 °C all the n -HOA-Cl organogels showed low viscoelasticity (100 Pa–5000 Pa). However, under isothermal conditions at temperatures between T Cr1 and T Cr2 , the 4 -HOA-Cl (i.e., at 113 °C or 106 °C) and 6 -HOA-Cl (i.e., at 102 °C) undergo a morphological transition from microplatelets to spherulites. In the case of 4- HOA-Cl this transition resulted in organogels with higher rheological properties (≈10,000 Pa) and melting temperature (125 °C–145 °C) than any of the other n -HOA-Cl organogels formed at 10 °C. The combination of viscoelasticy and high melting temperature shown by the 4 -HOA-Cl organogels is unique, and opens new alternatives to the use of organogels in food formulations (i.e., molecular gastronomy).