Evaluation of the mosaic model for polymer single crystals

Abstract

AbstractBy analogy with observed alteration of electron diffraction intensities from other crystalline long‐chain materials (e.g., paraffins) the mosaic model for polymer single crystals is evaluated. When many strong diffracted beams are excited simultaneously, the two‐beam dynamical diffraction theory (which then must be a consequence of the mosaic model) is shown not to be an adequate explanation of the electron diffraction intensities from such crystals; the n‐beam dynamical theory is much more adequate. Further, observed bend contours in these crystals indicate significant bend distortion. This is confirmed by observed modulation of diffraction intensities which are well explained by Cowley's model for diffraction from elastically bent crystals. Other experiments on these crystals reveal the bends to be irregular. Rocking curves reveal that bends also explain diffraction line broadening, as also proposed by White. The most accurate description of molecular organic microcrystals is therefore that of a deformed foil and not a mosaic.