INTERACTION BETWEEN 2-(1-NAPHTHYL)ACETIC ACID AND MICELLES OF NONIONIC SURFACTANTS IN AQUEOUS-SOLUTION

The interaction of 2-(1-naphthyl)acetic acid (NAA) with nonionic octylphenoxypoly(ethoxy)ethanol (Triton X) and linear primary alcohol (C-9-11) poly(ethoxy)ethanol (Neodol 91) surfactants was followed in an aqueous system by UV and fluorescence spectroscopy. There was a distinct shift of the UV absorption maximum to a longer wavelength at surfactant concentration-8 above the critical micelle concentration (cmc), indicating an intermolecular interaction between NAA and surfactant micelles. Both surfactant concentration and system pH had significant effects. NAA-surfactant interaction occurred only at surfactant concentrations above the cmc where micelles were present and the interaction was favored when the NAA molecule was in the nondissociated form (pH 3.2, pK(a) = 4.2). Equilibrium constants (K) for the NAA-micelle complex of the Triton X surfactants against buffer solution ranged from 80 to 1161, and log K was inversely related to the log of the number of oxyethylene units in the poly(oxyethylene) chain.