Structural refinement of the perfluorooctanesulfonate anion and its graphite intercalation compounds

The optimized structure for the perfluorooctanesulfonate (PFOS) anion is obtained using hybrid density functional theory (B3LYP) with basis set 3-21G*, and indicates a helical conformation of the carbon backbone and a chain twist angle of 20 degrees. From XRD data on a stage 2 CxPFOS prepared from mixed hydrofluoric acid-nitric acid solution, refinement gives chain orientation (60 degrees) and twist angles (16 degrees). CxPFOS samples prepared in 48% hydrofluoric acid are modeled using stage disorder, and peak width analyses indicate that these GICs correspond to solid solutions of 2nd and 3rd staging, with disorder-induced broadening increasing as the constituent stage fractions become similar in size.