Micellization and interfacial behavior of 16-E2-16 in presence of inorganic and organic salt counterions

The effect of salts (inorganic and organic) was investigated and analyzed to probe the micellization behavior of a biodegradable ester-bonded cationic gemini surfactant ethane-1,2-diyl-bis(N,N-dimethyl-N-hexadecylammoniumacetoxy) dichloride, referred to as 16-E2-16. We investigated the critical micelle concentration (cmc), free energy of micellization ( Δ G ° m ), free energy of adsorption ( Δ G ° ads ) and aggregation number Nagg of the gemini surfactant with different types of salts (KCl, KNO3, KSCN, NaBen, and NaSal). Indeed, our results clearly indicate that the two kinds of counterions (obtained from the respective salts) affect the aggregation behavior of 16-E2-16 in quite different ways and the order of ability to promote surfactant aggregation is found to be as NaSal > NaBen > KSCN > KNO3 > KCl. The counterions exert strong influence on the cmc, aggregation number and size and shape of aggregates of ionic surfactant systems. The results provide new insight in understanding the effect of ions on the delicate balance of forces controlling aggregate morphology and solution properties of charged amphiphilic molecules. The action mechanism of counterions has been investigated employing surface tension, viscosity, 1H NMR and fluorescence techniques.