Investigation of binary polymer/surfactant or ternary polymer/surfactant/Cu2+ complexes in aqueous solution through Nile red probing

The optical properties (absorption and emission) of Nile red have been widely used for staining or probing purposes in diverse aqueous systems. However, the applications of Nile red for the determination of the critical aggregation concentration of polymer/surfactant complexes or for the investigation of ternary polymer/surfactant/Cu²⁺ systems are very limited. The interactions between anionic polyelectrolytes and the oppositely charged surfactant N,N,N,N‐dodecyltrimethylammonium chloride were investigated in dilute aqueous solution, exploiting the optical properties of Nile red. It is shown that the emission properties of Nile red present better sensitivity than its absorption properties, concerning the detection of the hydrophobic polymer/surfactant complexes formed in aqueous solution. Moreover, it is found that the formation of ternary polymer/surfactant/Cu²⁺ complexes leads to a pronounced quenching of the luminescence of Nile red. The corresponding Stern–Volmer plots indicate that quenching is more favourable when coordination of Cu²⁺ ions with poly(sodium acrylate) takes place, as compared to simple electrostatic binding of these ions with poly(sodium styrene sulfonate). Nile red is a sensitive and accurate tool, as an alternative to pyrene, for the characterization of binary polymer/surfactant complexes or for obtaining information on the local arrangement of ternary polymer/surfactant/Cu²⁺ systems in aqueous solution. Copyright © 2010 Society of Chemical Industry