Study of Langmuir monolayers of crown-ether C₆₀ derivatives and their interaction with different subphase ions

The Langmuir monolayers of two crown-ether C₆₀ derivatives with different crown size (18-crown-6, and 15-crown-5) were studied by surface spectrophotometry and Brewster angle microscopy. The surface pressure-area (π-A) isotherms of the C₆₀ derivatives on pure water and different subphase ions were obtained. The limiting area of the isotherms depends on both the crown size and the presence of subphase ions. The larger crown size gave the larger limiting area of the isotherm. The addition of K^•, Ba^2• or NH₄^• to the subphase stabilized the monolayers and increased the limiting areas of the monolayer. Brewster angle microscopy shows different aggregation properties of crown-ether C₆₀ derivative monolayers on pure water compared with those on K^•, Ba^2• or NH₄^• subphases.