Salt-Induced Vesicle to Micelle Transition in Aqueous Solution of Sodium N-(4-n-Octyloxybenzoyl)-l-valinate

Abstract

The self-organization of a single-tailed amino acid based chiral surfactant sodium N-(4-n-octyloxybenzoyl)-l-valinate (SOBV) has been studied in water. A number of techniques like surface tension, fluorescence probe, dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) have been utilized for characterization of the self-assemblies. The amphiphile forms large spherical vesicles of 400−600 nm diameters in dilute aqueous solution. However, the vesicles get transformed into spherical micelles with increase of surfactant concentration or upon addition of relatively low amount (20 mM) of NaCl or KCl. This is the first example of salt-induced vesicle to micelle transition (VMT) in a single surfactant system. The vesicles are stable in the temperature range of 30−70 °C. Cleavage of intermolecular hydrogen bonds among the amide groups in the presence of salt appears to be the plausible cause for the VMT.