STRUCTURAL STUDIES OF SEMIFLUORINATED HYDROCARBON MONOLAYERS AT THE AIR WATER INTERFACE/

We report the results of experimental studies of the equation of state and structure of water-supported monolayers of the semifluorinated hy drocarbons F(CF2)(8)(CH2)(12)H, F(CF2)(10)(CH2)(11)H and F(CF2)(12)(CH 2)(18)H at temperatures from 4 to 30 degrees C. We find that monolayer s of these molecules are metastable to stable, and that the stability improves as the length of the fluorinated block increases. Grazing-inc idence X-ray diffraction measurements of the F(CF2)(12)(CH2)(18)H mono layer show that it is capable of forming ordered structures defined by hexagonal close packing of the fluorinated blocks of the adsorbed mol ecules. This monolayer undergoes slow relaxation, which is accompanied by increasing order and increasing macroscopic inhomogeneity. X-Ray r eflectivity studies of the F(CF2)(12)(CH2)(18)H monolayer were carried out on a flat area of the surface; an analysis of the reflectivity da ta reveals a hydrocarbon-down, fluorocarbon-up orientation for the F(C F2)(12)(CH2)(18)H molecule.