Micellization and Interfacial Behaviour of Amitriptyline-Nonionic Surfactant Systems in Aqueous Medium

By means of surface tension measurement (ring detachment method) mixed micellization and mixed adsorbed film formation were studied between an amphiphilic drug (amitriptyline hydrochloride – AMT) and nonionic surfactants (Tritons and Tweens) at different mole fractions. From the equilibrium surface tension measurements critical micelle concentration (CMC), maximum surface excess (Γmax) and minimum area per surfactant molecule at the air/solution interface (Amin) were obtained. The theories of Rosen, Rubingh and Maeda were applied to analyse the results. Different thermodynamic parameters, viz. free energy of micellization (ΔGo m), standard Gibbs energy of adsorption (ΔGo ads), and minimum energy of surface (Gmin) were evaluated. In the mixed micelles, presence of nonionic surfactants between the head groups of drug molecules decreases the repulsion among head groups. As a result, the CMC and Amin decrease while Γmax increases. Interaction parameters of micelles (βm) and monolayer (βs) indicate that the drug surfactant systems show better interaction at the interface than in micelles.