Robust Organogels from Nitrogen-Containing Derivatives of (R)-12-Hydroxystearic Acid as Gelators: Comparisons with Gels from Stearic Acid Derivatives†

Abstract

Thirteen members of a new class of low molecular-mass organogelators (LMOGs), amides, and amines based on (R)-12-hydroxystearic acid (HSA; i.e., (R)-12-hydroxyoctadecanoic acid) and the properties of their gels have been investigated by a variety of structural and thermal techniques. The abilities of these LMOGs, molecules with primary and secondary amide and amine groups and the ammonium carbamate salt of 1-aminooctadecan-12-ol, to gelate a wide range of organic liquids have been ascertained. Their gelating efficiencies are compared with those of HSA and the corresponding nitrogen-containing molecules derived from stearic acid (i.e., HSA that lacks a 12-hydroxyl group). Several of the HSA-derived molecules are exceedingly efficient LMOGs, with much less than 1 wt % being necessary to gelate several organic liquids at room temperature. Generally, the self-assembled fibrillar networks of the gels consist of spherulitic objects whose dimensions depend on the protocol employed to cool the precursor sol phases. X-ray studies indicate that the LMOG molecules are packed in lamellae within the fibers that constitute the spherulites. In addition, some of the organogels exhibit unusual thixotropic properties: they recover a large part of their viscoelasticity within seconds of being destroyed by excessive strain shearing. This recovery is at least an order of magnitude faster than for any other organogel with a crystalline fibrillar network reported to date. Correlations of these LMOG structures (as well as with those that lack a hydroxyl group along the n-alkyl chain, a headgroup at its end, or both) with the properties of their gels, coupled with the unusual theological properties of these systems, point to new directions for designing LMOGs and organogels.