Gl. Liang et al., MOLECULAR-DYNAMICS SIMULATIONS OF THE HEXAGONAL STRUCTURE OF CRYSTALSWITH LONG METHYLENE SEQUENCES, Journal of polymer science. Part B, Polymer physics, 31(13), 1993, pp. 1909-1921
An unconstrained polymethylene crystal, consisting of 9600 CH2 groups,
in which each CH2 is permitted to carry out stretching, bending, and
torsional motion, has been studied at various temperatures using molec
ular dynamics simulations. Information about the atomistic details of
the dynamics and structure of these crystals is presented. A significa
nt disorder exists at temperatures well below the melting point. Close
to melting, the disordered crystals have about 2% of gauche bonds tha
t are distributed mainly at positions close to the surface of the crys
tal. The major disorder consists, however, of a collective twisting of
the chains leading to a hexagonal crystal structure. The hexagonal st
ructure of the symmetric motifs is caused by a dynamic multidomain arr
angement of the chains. (C) 1993 John Wiley & Sons, Inc.