Continuous diffuse scattering from polymethylene chains - an electron diffraction study of crystalline disorder

Continuous diffuse scattering is noted in electron diffraction patterns from polymethylene compounds such as n-paraffins and polyethylene. In a projection down the chain axes, experimentally produced by solution crystallization, the diffuse scatter in hk0 patterns disappears at low temperature, in accord with a thermal-diffuse-scattering model, which explains the intensity distribution and its temperature dependence. For a projection onto the chain axes, experimentally achieved by epitaxic orientation on benzoic acid crystals, the 0kl, as well as 3D projections, contain diffuse scatter which does not disappear at low termperature. Its origin appears to be due to frozen-in longitudinal chain static displacements, perhaps as much as 0.25 Å, as indicated by a model for this disorder.