Imaging of different crystal planes in oriented polyethylene by atomic force microscopy

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Abstract
Atomic force microscopy (AFM) images of uniaxially stretched ultrahigh-molecular-weight polyethylene has unveiled molecular resolution on the surface of the microfibrils which were formed during the orientation process. A series of AFM scans with molecular resolution produced two types of photomicrographs: one set has an average distance between the neighbouring chains of 7.3 Å and the other set has an average distance of 4.9 Å. These intermolecular distances, which can be observed on the surface of the same microfibril, correspond to the a (7.417 Å) and b(4.945 Å) repeat lengths of the crystal unit cell. Based on these results it is concluded that the (010) and (100) crystallographic planes of polyethylene were imaged. The good agreement between the expected and observed crystal structure parameters suggests that within the experimental accuracy no relaxation of the molecular packing on the surface of microfibrils occurred.