Polymer crystal fold surfaces, epitaxial crystallization

Epitaxy Involving Fold Surfaces of Polymer Crystals, 254... 

As indicated, epitaxial crystallization implies contact planes of the substrate and deposit that are crystallographic. In polymers, only hkO planes should be considered since they are parallel to the chain axis. By contrast, planes of type hkl cut the chain axis, which does not generate an exposed, free contact face, since the chains continue on both sides of the plane, possibly with a change in orientation, as in kink-bands. However, exposed planes of type hkl exist in polymer crystals, as they are associated with chain folding. This lamellar folds surface is by necessity disordered or, at least, not crystallographically ordered. A priori, the folds surface would not be thought of as a contact plane in any epitaxial crystallization. However, a few examples of epitaxies that involve the end, fold surface of polymer crystals have been reported. 

Figure 8.12 Polymer decoration epitaxial crystallization on the fold surface. Polyethylene vapors were deposited on the surface of single crystals of polyoxymethylene (POM) at room temperature. The resulting PE decoration is made of edge-on lamellae oriented normal to the POM growth faces, with the deposited PE chains parallel to the growth front. The distance between POM fold planes (0.386 nm) imposes the monoclinic (010) PE contact plane, in which chains are separated by =0.4 nm [68].

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