Epitaxy of folds in polyethylene crystals: molecular mechanics investigation

In the prevailing thermodynamics associated with Gibbsian surface physics of a century ago, the surface of a crystal has an associated surface energy and surface stress that influences properties and morphology. This work uses molecular mechanics to investigate the surface energy and epitaxial packing of chain folds on the surfaces of adjacent crystals. It is shown that there are lower energy juxtapositions of the crystals resulting from energetically favorable epitaxial arrangements. These lower the excess surface energy with respect to the melt, but do not completely eliminate the discrepancy between the values of the surface energy from computational results and analysis of experimental data. The epitaxial arrangements are consistent with the experimentally observed rotational displacement of successive layers in multi-layer polyethylene crystals. Thus, they might influence the rotation of the successive layers resulting from screw dislocations.