Fluidity of binary monolayers of semi-fluorinated and non-fluorinated fatty alcohols at the air−water interface

Abstract

Abstract The focus of this study is to elucidate lateral interactions between pentadecanol (H15OH) and (perfluorohexyl)nonanol (F6H9OH) at the air–water interface. The surface pressure (π)−molecular area (A) and surface potential (ΔV)−A isotherms of the binary monolayer were measured as a function of mole fraction. The excess Gibbs free energy of mixing was calculated from the π−A isotherms. In addition, a two-dimensional phase diagram of the system was constructed by analyzing the isotherm data. These results suggested miscibility between the two components. Furthermore, the addition of F6H9OH induced the fluidization and stabilization of H15OH monolayers at the low and high surface pressures, respectively. The phase behavior upon monolayer compression was visualized with in situ fluorescence microscopy and ex situ atomic force microscopy. A combination of both the microscopic images was successful in capturing the evidence of the two-component miscibility and phase transition at large F6H9OH mole fractions.