2013/09/26 by Alan K. Soper, A K Soper, Soper, A K +6
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Nuclear Physics and Applications #Polymer Nanocomposites and Properties #Soft Condensed Matter (cond-mat.soft) #X-ray Diffraction in Crystallography #cond-mat.soft
paper · pdf · doi:10.48550/arxiv.1309.6943
arxiv created 2013/09/26 · openalex publication_date 2013/09/26 · arxiv updated 2013/09/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Empirical potential structure refinement (EPSR) simulations are performed on total neutron scattering data from powder samples of polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), both at 300K. For PTFE a number of Bragg peaks are visible in the scattering data and these are found to be consistent with a lattice spacing a(=b)=5.69(1)Å with a dihedral angle along the (helical) chain of 166^∘ which gives a repeat distance along the chain (c-axis) of ∼19.6Å. The positions of the Bragg peaks are well reproduced by this model, although there is a mismatch in the amplitudes of some of the higher order reflections between simulation and data. For PCTFE there is only one visible Bragg peak (100) which is well reproduced by a hexagonal lattice of atactic parallel polymers with a spacing of a(=b)=6.37(1)Å. In this case the absence of distinct reflections along the polymer c-axis makes characterisation of the internal dihedral angle difficult, but a model with nearly straight trans (zig-zag) structure gives best agreement with the data. For PCTFE little change in structure could be discerned when the material was heated to 550K, apart from a slight increase in lattice spacing. In both cases there is substantial diffuse scattering between the Bragg peaks, and this is correctly replicated by the EPSR simulations.