Molecular dynamics in perfluoro-n-eicosane. I. Solid phase behavior and crystal structures
- 15 August 1991
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 95 (4) , 2800-2806
- https://doi.org/10.1063/1.460931
Abstract
Perfluoro‐n‐eicosane (n‐C20F42) passes through three different solid modifications, called M(TI(146<T200 K). Structures of the phases M and R were characterized by x‐ray scattering experiments. Crystals are built up by rectangular layers. In modification M layers are set up by arrays of right‐handed and left‐handed (15/7‐) helices in alternate succession. The unit cell is monoclinic (a=9.65 Å, b=5.70 Å, c=28.3 Å, and β=97°; space group Pa). In modification R molecules are highly mobile. There is no ordering with regard to the helix handedness. Molecules resemble cylindrical objects and are packed in a hexagonal dense mode. Regular layer stacking results in crystals with rhombohedral symmetry (a=b=5.70 Å, c=85.00 Å, γ=120°; space group R3̄m).Keywords
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