A spontaneous phase transition from reverse micelles to organogels due to surfactant interactions with specific benzenediols

Hydrogen-bonding interactions between suitable phenols and the head group of the twin-tailed anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT), form the basis for a novel class of organogels. The gels are novel in that very small quantities of these low molecular weight solutes are sufficient to cause gelation. Previous work has shown that the gel-forming propensity of the phenol is determined by its acid strength and also the substitution pattern on the aromatic ring. Evidence suggests that the underlying molecular architecture of these gels consists of strands of stacked and motionally restricted phenol molecules. The surfactant appears to be linked through hydrogen bonding to the external surface of the stack and its motion is relatively unrestricted. Here, we report the finding that the gels also form with select benzenediols (resorcinol derivatives). Interestingly, these gels are much stronger than some of the strongest gels made with phenols under similar conditions. A combination of NMR and FTIR spectroscopic evidence suggests that these gels derive their strength from binding with both carbonyl groups of the surfactant, whereas in the gels made with phenols, only one carbonyl group is bound. The stacked phenol microstructure of the organogels proposed previously seems to be generally valid for the case of gels formed with the benzenediols. The additional possibility of bridging the adjacent phenol molecules in the stack by the adsorbed surfactant allows for a ''scaffolding'' around the aromatic stack. (C) 1997 Elsevier Science B.V.