Interfacial and micellar properties of mixed systems of tricyclic antidepressant drugs with polyoxyethylene alkyl ether surfactants

The aqueous mixed systems of tricyclic antidepressants: nortriptyline hydrochloride (NOT) and amitriptyline hydrochloride (AMT) with nonionic polyoxyethylene alkyl ether surfactants: C10E8/C10E10 have been studied to determine the micellar and interfacial behavior and various experimental techniques like surface tension, fluorescence and cloud point have been employed. The micellar, interfacial and thermodynamic parameters like critical micelle concentration (cmc), interaction parameter (β), maximum surface excess concentration (Гmax), surface pressure at cmc (Πcmc) and minimum area per molecule (Amin), aggregation number (Nagg), Gibbʹs free energy of micellization (ΔGm), Gibbʹs free energy of adsorption (ΔGads), excess free energy of micellization (ΔGex) have been evaluated. The negative values of interaction parameter obtained from regular solution theory suggest the synergistic interactions in all the proposed mixed systems. The negative values of ΔGm and ΔGads show that micelle formation and adsorption at the air/water interface is energetically favorable. The higher values of aggregation number show the existence of hydrophobic interactions and supports synergism. The cloud point measurements have also depicted enhancement of hydrophobicity in the mixed micelles with an increase in concentration of nonionic surfactants.