Probing the self-aggregation behavior and counter ion distribution of a copper surfactant complex

Abstract

In the present work, a new copper surfactant complex [Cu(BrCl₂)(C₁₂H₂₅N(CH₃)₃)] was synthesized and characterized. Its organization at the air–water interface and in bulk aqueous medium was investigated. The aggregation behavior and adsorption pattern of the metallosurfactant revealed important information about the molecular organization and counter ion distribution, which until now was unknown. The critical micellization concentration and optical thickness of the copper surfactant were determined using surface tension, cyclic voltammetry and ellipsometry techniques. The X-ray absorption fine structure technique was applied to the copper surfactant solution under both total reflection (TRXAFS) and transmission conditions to understand the ion organization at the interface and in the bulk, respectively. The Br and Cu K-edge absorption revealed the presence of Br⁻ ions and the absence of Cu²⁺ ions at the interface and in the inner core of micelles. Furthermore, Br⁻ ions were found to exist in two solvation states, designated as “free-Br” and “bound-Br”. Even the surface excess concentration of the ions was precisely determined from the adsorbed film of copper surfactant using external reflection absorption (ERA)-FTIR spectroscopy.