Effect of anion type on monolayers and Langmuir-Blodgett films of gadolinium stearate

This work is focused on the preparation and characterization of gadolinium- containing stearic acid (SA) Langmuir-Blodgett (LB) films. SA monolayer beh avior on the gadolinium-containing aqueous subphase has been analyzed by th ermodynamic measurements. The compression isotherm shape changed substantia lly under varying anion type at the constant rare-earth cation content and pH in aqueous subphase. Those changes were ascribed to different monolayer surface charging under gadolinium binding. Small angle X-ray diffraction wa s used to study the structure of formed multilayer rare-earth-containing LB films. Considerable structural defects in multilayer LB films were found w hen gadolinium chloride solution was exploited as aqueous subphase for LB h im formation, caused presumably by electrostatic interactions under charged monolayer deposition. The use of monodentate complexions like acetic acid residue was proposed to form bulk phase low-charged complexes with trivalen t cations. The electroneutral ligand exchange reactions of such complexes w ith fatty acid Langmuir monolayer results in the formation of quasi-neutral trivalent cation complexes bound to the monolayer surface. This approach a llowed effective neutralization of the monolayer surface under gadolinium b inding and formation of condensed monolayer below the triple-point temperat ure. The compression and subsequent deposition of such monolayers resulted in the formation of highly ordered LB films with high content of adsorbed g adolinium cations arranged in two-dimensional (2-D) monatomic layers. (C) 2 000 Elsevier Science B.V. All rights reserved.