Molecular dynamics simulation of the temperature dependence of lattice parameters of alkane crystals during cooling

Abstract

The cooling of a crystal of 192 pentacontamethylene chains has been followed by molecular dynamics simulation after instantaneous heating to various temperatures and cooling to 335 K at 0.8 K ps^–1 after heating to 436 K. The latter temperature is above the melting point of pentacontane 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 on the changes in the simulated crystal has been extended by quantitative evaluation of the crystal parameters. The nature of the then-suggested hexagonal phase is discussed. On cooling, a transition of the crystal from a hexagonal α-phase with freely ‘rotating’ chains to tilted monoclinic β_M-phase with large-amplitude chain fluctuations has been identified between 370 and 360 K with a gain of 1% in density.