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.

Gelled polymerizable microemulsions. Part 3 Rheology

“…12-HOA is a well-known low molecular mass organic gelator (LMOG), which is capable of forming strong organogels with some solvents. 4,[7][8][9] As the phase diagram of the binary system 12-HOA -ndodecane has not been studied in detail yet, we determined the sol-gel transition temperatures T g as a function of the gelator mass fraction β in order to have a reference for the discussion of the gelled microemulsions. The results are represented in Fig.…”

“…Binary 12-HOA organogels were found to consist of a rigid fibrillar network with rigid junction zones. Both the fibrils and the junctions are crystalline 4,[8][9][10] and are generated via self-assembly of 12-HOA molecules, which is why the resulting gel network is called a self-assembled fibrillar network (SAFIN).…”

Low-molecular-weight organogelators as functional materials for oil spill remediation

“…The relationship between the properties of the molecular gels formed from 12-HSA derivatives was extensively studied with different chemical structures by Rogers and Weiss (16a-16g, 17a-17f, 18a-18d). [29][30][31] Weiss's group also reported systematic studies of simple LMWGs and many organogelators that may be applicable for oil spill remediation and confirmed the formation of organogels composed of hydrophobic solvents, a liquid n-alkane (as a model for petroleum oil) and a gelator (longer n-alkanes C24, C28, C32 and C36, 19a-19g). [32] Moreover, they conducted a series of studies on organogels to clarify the influence of chemical modification of the n-alkane on its gelation ability, including the behavior of derivatives with amide 16a, 16d, 16e, [28] urea 20a-20i and thiourea 21a-21f, [33] and collected ample analytical data.…”

Effects of Cooling Rates on Self-Assembling Structures of 12-Hydroxystearic Acid in an Ionic Liquid

“…12-HSA samples were purchased from Wako Chemical Co. The samples were purified by repeating recrystallization several times with a mixture of hexane/ethyl acetate = 95/5 wt/wt% [18]. In addition, 12-HSA samples with high purity were kindly supplied from Kusumoto Chemicals Co. Ltd. We used 1-allyl-3-butylimidazolium bis(trifluoromethanesulfonyl) imide [ABIm][TFSI] (Kanto Chemical) as a solvent.…”