Deformation and defects in (SN)× lattice strain and fibrillation

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Abstract
The fine structure of deformed areas of thin (SN)× crystals has been observed using transmission electron microscopy. Prominent features are (a) broad bands due to local buckling, (6) fine ( 40 A) striae running perpendicular to the chain axis and (c) fine (∼ 60 A) lineage parallel to the chain axis. In areas in which rupture has occurred parallel to the chain axis a fine fibrillation (∼ 38 A) is observed. The nature of the contrast effects for the striae is described and it is concluded that they represent local and repetitive deviations from the Bragg periodicity. A lattice-distortion model in which the polymer chains receive a repetitively reversed helical twist is consistent with the physics of the deformation and the observed deviations from classical Bragg conditions. The helical twist can result either from small, continuous deviations of the rotation angle or by a more localized defeet of the same character, and results in a shortening of the chain. The periodicity of the lineage and fibrillation microstructures probably both reflect a defoct structure introduced during polymerization.