Self-Consistent-Field Lattice Gas Model for the Surface Ordering Transition ofn-Hexadecane

It is known from experiments that the solid-liquid phase transition of $n$-alkanes involves surface freezing. On cooling, a monomolecular surface layer crystallizes first. Upon further cooling, the bulk solidifies. The orientational ordering aspect of $n$-hexadecane freezing is modeled with a self-consistent-field lattice gas theory, showing that both events are first-order transitions. It is assumed that the C${\mathrm{H}}_3$ segments are more surface active than the C${\mathrm{H}}_2$ ones. This initiates at high $T$ a slight orientational bias, but at low $T$ a cooperative alignment of the ${\mathrm{C}}_{16}$ perpendicular to the interface.