To rationalise this behaviour we calculated the VDOS for the hematite and PAO4 regions adjacent to the interface as well as the overlap integral of the two spectra. We observed no significant changes in the vibrational spectra for the hematite or PAO4 regions or the overlap integral as the strength of the interactions were increased. However, we observed that a significant increase in the first adsorption layer density of the fluid as the strength of the solid-liquid interactions was increased. We therefore conclude that the decrease in ITR arises, not from changes in the vibrational spectra of the two components, but from the increased density of PAO4 molecules close to the surface as the solid-liquid interaction strength was increased.