Disorder at the bilayer interface in the pseudohexagonal rotator phase of solidn-alkanes

Abstract

Molecular-dynamics calculations are used to characterize the structure and dynamics of the two solid bilayer phases of the n-alkane tricosane (${\mathrm{C}}_{23}$ ${\mathrm{H}}_{48}$). In the crystalline orthorhombic phase at 38°C, chains undergo translational, rotational, and torsional motions, but are otherwise essentially all-trans and perfectly ordered with a herringbone packing. By contrast, at 42°C, in the pseudohexagonal (rotator) phase, there is a dramatic increase in longitudinal chain motion, each chain now has four possible orientations and a significant number of conformational defects develop, predominantly at the chain ends.