Wormlike micellar and vesicular phases in aqueous solutions of single-tailed surfactants with aromatic counterions

The aggregation behavior of a series of alkyltrimethylammonium 5-ethylsalicylate surfactants (CnTA5ES, n = 12, 14, 16) in aqueous solution has been investigated employing turbidity measurements, fluorescence anisotropy experiments (using 3-hydroxynaphthalene-2-carboxylate, HNC-), and cryo transmission electron microscopy (cryo TEM). Critical aggregation concentrations (cac) were determined by surface tension experiments; they are smaller than those of their salicylate analogues. CnTA5ES surfactants form vesicles immediately above the cac rather than wormlike micelles such as their salicylate counterparts. C12TA5ES was found to form large unilamellar vesicles (LUVs) which transformed into surfactant layers upon increasing surfactant concentration. The transition was characterized by an increase in turbidity. C14TA5ES and C16TA5ES were found to form LUVs and long wormlike vesicles which are assumed to be responsible for the viscoelasticity of the solutions. Upon increase of the surfactant concentration, a t...