Interaction of copper ions with stearic acid Langmuir monolayers and formation of cluster structures in monolayers and Langmuir-Blodgett films.

The interaction of copper ions with a stearic acid Langmuir monolayer resulting in an extremely high level of copper binding to the monolayer in amounts much larger than the number of stearic acid molecules in the monolayer was studied. The shape of the pressure-area isotherm changed drastically upon pH changes from 4 to 6 in the presence of copper ions in the aqueous phase (at concentrations of 10(-5) to 10(-3)(M) or upon addition of copper ions to the aqueous phase under different monolayer compressions. The copper ion concentration changes in the bulk phase, caused by binding to the monolayer, were studied by EPR at the equilibrium after intensive mixing of the bulk phase and were found to depend on pH of the aqueous phase and the extent of monolayer compression. The highest level of binding (up to 100 copper ions per stearic acid molecule, pH 5.6, initial copper concentration 5.10(-4) M) was observed at a surface pressure of about 20 mN/m; further compression of the monolayer and the respective increase in surface pressure caused the reverse growth of aqueous phase copper ion concentration. At the collapse and destruction of the monolayer, the copper ion concentration in the bulk phase was similar to that in the absence of the monolayer. The EPR spectra and SAXS diffractograms of copper-containing stearic acid monolayers confirmed the high copper content in LB films obtained. An STM study of pure stearic acid and the copper-containing monolayer LB films, transferred to graphite wafers from the water subphase surface (pH 5.4) at various copper concentrations, discovered nanosized (about 5 nM) cluster formations on the monolayer surface. The data obtained indicate that the interaction of a charged Langmuir monolayer with copper ions and formation of copper-containing nanostructures depends on monolayer compression and is determined by the arrangement, order, mobility of the monolayer stearic acid molecules and by electrostatics at the interface.