Some new habit features in crystals of long chain compounds. Part II. Polymers

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Abstract
The morphology underlying the characteristic striations observed in polymer crystals has been examined in more detail that hitherto. The striations were found to correspond to corrugations in the crystal layers. Both pleat and roof-ridge corrugations were observed in polyethylene crystals. These latter are pictorially similar to those in paraffin crystals discussed in Part I. The analogy between the two cases is pursued with the folds replacing the end groups in the polyethylene case. A possible common origin for both types of corrugation is proposed to be the collapse of non-planar crystals. A particular non-flat-based pyramidal model is proposed. Evidence for the existence of such crystals is presented. A variety of observations, including the non-planar crystals, is shown to be explainable in terms of a particular type of packing of the folded molecular chains. Further, it is suggested that if folding also occurs in the bulk polymer, then roof ridges of the type discussed might account for its well-known four-point low-angle x-ray pattern.