Formation, structure, and morphology of triazole-based Langmuir-Blodgett films

The formation, morphology, and structure of two-dimensional Langmuir-Blodgett (LB) assemblies of octadecyltriazole (ODT)-based metal-containing oligomers presenting, in the case of iron, the spin-crossover phenomenon is studied with Brewster angle microscopy, IR dichroism, X-ray diffraction, and atomic force microscopy. Two processes occurring at the air-water interface are confirmed to dominate the mechanism of formation of these LB films, the instability of the coordination polymers at the air-water interface and recoordination of metal ions in the subphase at the interface during the LB deposition process. The Langmuir film allowing the LB film formation is mostly made of ODT. The films do present a lamellar structure in which the ODT molecules are tilted and incorporate coordinated isolated metal ions and oligomers of metal ions. The morphology of the LB films is globally flat but with a rather high roughness resulting from inhomogeneities related to phenomena occurring during the LB film formation. These observations are in agreement with the relative affinity of the metal ions with ODT and the relative stability of the coordination polymers at the air-water interface, which have been determined for the group Cu-Fe-Co-Ni.