Molecular dynamics in perfluoro-n-eicosane. II. Components of disorder

Abstract

The defect structure in the rhombohedral modification R of perfluoro-n-eicosane has been analyzed in a temperature-dependent x-ray and neutron scattering study. The analysis was based on an evaluation of Bragg-reflection intensities and of the diffuse scattering. Different components of disorder were detected and characterized. At the transition from the low temperature phase to modification R, rotation of the molecules about their long axes sets in. As shown by the azimuthal distribution of the diffuse scattering, rotations occur cooperatively with correlations between neighbors. The Debye–Waller factors measured for the layer reflections are indicative for a moderate roughening of the interfaces due to a restricted longitudinal diffusive motion. Molecules are perturbed by the formation of helix reversal defects. Evaluation of the diffuse scattering yields the associated finite azimuthal correlation length. There is also evidence for a continuous slow untwisting of the helix. With increasing temperature, it approaches the all-trans form.

Phase-transition behavior ofn-alkanes on nanostructured polytetrafluorethylene films: Brillouin spectroscopic and calorimetric investigations on pentacosane

“…are due to a complicated interaction of intramolecular and intermolecular instabilities. [1][2][3][4][5] Usually the structural transitions in these systems have an order-disorder as well as a displacive character. This is reflected by acoustic as well as by thermal properties.…”

Chemical force microscopy for hot-embossing lithography release layer characterization

“…35 Despite their rigidity, intermolecular interactions provide for complex behaviour of fluorocarbon Langmuir monolayers 36,37 and solid-solid phase transitions are observed. 38 Hydrofluoroalkyl chain behaviour and properties are usually intermediate between the corresponding saturated hydrocarbon and perfluoroalkyl species. 28 Very recent 19 F NMR studies of perfluoroalkanoate SAMs on zirconia suggest that there is no evidence of chain melting at temperatures well above the T m of bulk materials and that enhanced SAM mobility is a result of molecular reorientations around the long chain axis.…”

Fluorous Property of a Short Perfluoroalkyl-Containing Compound Realized by Self-Assembled Monolayer Technique on a Silicon Substrate

“…1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS; Rf7) (>96.0%) was purchased from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). 5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13,14,14,14-Henicosafluorotetradecanoic acid (My-Rf9) for the discussion of the LB technique was synthesized as reported in our previous paper. 6 The Si substrate was purchased from Valqua FFT Inc. (Tokyo, Japan) and cleaned in a conventional manner: sonication in pure water, ethanol, acetone, and dichloroethane for about 1 min each.…”

“…2,3 To discuss the molecular interaction of Rf groups in a physicochemical manner, we have to pay attention that each C-F bond has a large permanent dipole moment due to the large electronegativity of fluorine 3 , and in addition, an Rf group has a helical conformation about the molecular axis. 4,5 As a result, the Rf groups having the length of (CF2)7 or longer are spontaneously aggregated to yield "two-dimensional dipolearrays with various directions," which is a dipole-array network. This spontaneous aggregation mechanism is known to be the stratified dipole-arrays (SDA) theory.…”