In situ formation and dispersion of lanthanide complexes in wormlike micelles
Lanthanide-containing, water-based fluids normally suffer from low photoluminescent (PL) and/or colloidal stability, which greatly hinders their applications. Herein, we report the preparation of PL fluid which contains in situ formed europium complexes in aqueous solution. The strategy first relies on the construction of wormlike micelles by mixing a zwitterionic surfactant (tetradecyldimethylaminoxide, C14DMAO) and a tridentate ligand for lanthanide cation (2,6-dipicolinic acid, DPA) in water. The addition of the dual-functionalized DPA to aqueous solution of C14DMAO (100 molL-1) induced non-monotonic rheological changes, with the expected formation of pseudogemini surfactant at a DPA-to-C14DMAO molar ratio of approximately 1:2. When a third component of EuCl3 is introduced to this system, complexes formed in situ between Eu3+ and DPA, resulting in bright red-emission. Besides DPA, C14DMAO also attends in the complexation, which squeezes out water molecules and greatly improves the PL stability of the fluid. The synergetic effect among Eu3+, DPA and C14DMAO leads to high colloidal stability of the fluid, opening the door for a wide range of potential applications. Further tests indicate that this strategy can be easily expanded to other lanthanide cations such as Tb3+.