Effect of Salt on the Micellization of Partially Fluorinated Octylesters and Hydrogenated Dodecylesters in Water

The effect of added salt, NaCl, on micellization and structural properties of four enantiomeric/racemic surfactant pairs obtained from partially fluorinated octylesters (PFOEs) and hydrogenated dodecylesters (DDEs) of alanine and serine were investigated by electrical conductivity, surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The Krafft temperatures, the critical micelle concentrations, the degree of counter-ion ionization, and the Gibbs free energy of micellization were determined. The Gibbs free energy of adsorption of the esters at the air/solution interface was greater than that of micellization. The hydrodynamic radius (RH) increased with salt concentration, and the polydispersity index exhibited a shift from monodisperse to polydisperse aggregates. The PFOEs of serine could incorporate only a minimum amount of salt, but it exhibited the largest R-H (37.9 nm). DLS and TEM results indicated that the esters formed micelles of spherical shapes. Neither of the methods could detect an appreciable difference in the micelle sizes of the L- and DL- amphiphiles. The DDEs exhibited greater antibacterial activity against some gram-positive bacteria than the reference antibiotic, tetracycline, but the PFOEs did not show any activity.