Self-consistent-field calculation of structures and static properties of the solid-fluid interface: Paraffinlike molecule systems

The interfacial structure and interfacial properties were investigated within the framework of an inhomogeneous cell model, using self-consistent-field calculations. For interfacial systems consisting of completely flexible chain molecules, profiles of the segment density of fluid molecules vanish exponentially versus distance z from the solid surface. It can be shown that the structure of the solid-fluid interface can be characterized by two key factors: the surface scaling factor Cₗ* and the characteristic thickness of the interface n*. In contrast, the exponential law cannot be applied to interfacial systems consisting of molecules with somewhat rigid chains. For those systems, the ordering and the layering of chain molecules occur at the solid-fluid interface, due to the energy and the entropy effect. In addition to the factor Cₗ*, the structure of the solid-fluid interface of the system may qualitatively be related to half of the chain length of solute molecules and of solvent molecules. Finally, the calculated values of Cₗ* are compared with the experimental ones for a variety of n-paraffin systems. The results are very satisfactory.