There was no attempt to control the atmosphere in the contact angle experiments for PAO on steel discussed above and the relative humidity was not reported. To cover the possible range of surface configurations in the experiments, we use fully hydroxylated surfaces and water nanofilms with coverages ranging from 0-4 ML, which in the absence of a PAO4 layer corresponds to RH values of 5-95%. Top-down views of the water films for the different water coverages (0.5-4 ML) are shown in Figure (a)-(e) We show the interfacial structure of these nanoflims and demonstrate their important role in determining the work of adhesion in experimental systems, namely the hydroxylated α-Fe 2 O 3 (0001)/PAO4 interface. To quantify the surface wettability, we employ state-of-the-art computational methods based on the drysurface approach. Following our previous study, 10 PAO4 is represented by hydrogenated 1-decene trimer molecules modeled with the LOPLS-AA force-field (FF) and the internal surface interactions are from INTERFACE-FF. Parameters from Clay-FF 14 are used for the hydroxyl groups, and the SPC/E model 33 is used for the water molecules. For the solid-liquid interface, we compare three potentials with relatively weak (Clay-FF ), intermediate ), and strong (Savio et al. ) Lennard-Jones interactions.