The structure of liquid heptane at wax surfaces

The properties of the molecules in a liquid heptane film on an octacosane c rystal surface have been studied using molecular dynamics techniques. Molec ule energies, conformational properties and dynamic properties were calcula ted and correlated with height above the crystal surface. This analysis ind icated that the liquid heptane is strongly ordered in the vicinity of the w ax surface, showing at least four layers in which the heptane tended to ali gn parallel to the surface. Substantially more structure was found in the i nterfacial heptane layer, with the heptane also being aligned parallel to t he paraffin molecules in the wax surface, and showing a strongly anisotropi c diffusive behaviour that reflected the underlying topology of the wax sur face. Simulations were also performed to study the effect of an adsorbed co mb-shaped polymer (poly(octadecyl acrylate)) on the liquid properties. The polymer was found to mix with the heptane to produce an additional, strongl y ordered layer that would provide a kinetic barrier to any subsequent wax deposition.