Balance of Coordination and Hydrophobic Interaction in the Formation of Bilayers in Metal-Coordinated Surfactant Mixtures

Abstract

Metal–ligand coordination and hydrophobic interaction are two significant driving forces in the aggregation of mixtures of M^<i>n</i>+ surfactants and alkyldimethylamine oxide (C_<i>n</i>DMAO) in aqueous solutions. The coordinated systems exhibit rich aggregation behavior. This study investigated the effect of M^<i>n</i>+ ions (Zn²⁺, Ca²⁺, Ba²⁺, Al³⁺, Fe³⁺, La³⁺, Eu³⁺, and Tb³⁺) and hydrophobic chains (hydrocarbon and fluorocarbon) on the formation of metal-coordinated bilayers. We found that fluorocarbon chains and branched hydrocarbon chains are preferable to the corresponding linear hydrocarbon chains for the formation of an L_α phase. Moreover, L_α phases formed by fluorocarbon chains exhibited higher viscoelasticity than ones formed by the hydrocarbons, and the bilayers formed by branched chains were rather flexible, revealing obvious undulation. The construction of bilayers was also strongly affected by metal ions due to their variable coordination ability with C_<i>n</i>DMAO. Our results contribute to the understanding of the formation of metal-coordinated bilayers, which is driven by the interplay of noncovalent forces