MOLECULAR-DYNAMICS SIMULATION OF THE TEMPERATURE-DEPENDENCE OF LATTICE-PARAMETERS OF ALKANE CRYSTALS DURING COOLING

The cooling of a crystal of 192 pentacontamethylene chains has been fo llowed by molecular dynamics simulation after instantaneous heating to various temperatures and cooling to 335 K at 0.8 K ps(-1) after heati ng to 436 K. The latter temperature is above the melting point of pent acontane C50H102, T-m = 365 K). The earlier report by G. L. Liang, D. W. Noid, B. G. Sumpter and B. Wunderlich, Acta Polym., 1993, 44, 219 o n the changes in the simulated crystal has been extended by quantitati ve evaluation of the crystal parameters. The nature of the then-sugges ted hexagonal phase is discussed. On cooling, a transition of the crys tal from a hexagonal ct-phase with freely 'rotating' chains to tilted monoclinic beta(M)-phase with large-amplitude chain fluctuations has b een identified between 370 and 360 K with a gain of 1% in density.