Effect of salt additives on the aggregation behavior and morphology of 14-E2-14

Abstract

A biodegradable ester-bonded cationic gemini surfactant (ethane-1,2-diyl bis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride), referred to as 14-E2-14, was synthesized whose aggregation behavior in aqueous solutions in the presence of salts (KCl, KNO3, KSCN, sodium benzoate (NaBen), and sodium salicylate (NaSal)) was studied using tensiometric, viscometric, fluorimetric, and nuclear magnetic resonance (NMR) measurements. Various parameters such as CMC, maximum surface excess (Гmax), minimum surface area per molecule (Amin), standard Gibbs free energy of adsorbtion (ΔGadso)/micellization (ΔGmo), and aggregation number (Nagg) were calculated. It was observed that the ability to promote surfactant aggregation decreased in the order NaSal>NaBen>KSCN>KNO3>KCl. Experiments have shown that the salt counterions exert a strong influence on the CMC, aggregation number, and size and shape of aggregates. 1H NMR measurements have provided detailed information in context of the action mechanism of the counterions wherein the formation of nonspherical micelles at relatively low surfactant concentrations is deduced. Furthermore, the 1H NMR studies have been found useful in locating the salt counterions, especially Ben− and Sal−.