Disorder in the pseudohexagonal rotator phase of n-alkanes: molecular-dynamics calculations for tricosane

Abstract

Molecular-dynamics calculations for a flexible-chain model have been used to study two, solid, bilayer phases of the n-alkane tricosane (C₂₃H₄₈). In the crystalline, orthorhombic phase at 311 K, the chains remain all-trans and fully ordered, with a herringbone packing. By contrast, in the pseudohexagonal (R _I) rotator phase at about 320 K, a dramatic increase in longitudinal chain motion is observed, each chain has four well-defined orientations, and a significant number of conformational defects develop, with the latter occurring predominantly at the chain ends. The results of the simulations are in excellent agreement with experiment.