despite the lower contact angle (θ sp = 10.9 • ). It should be noted that the contact angles of steel and other surfaces are quite sensitive to the presence of surface contaminants such as water and hydrocarbons. However, separate experiments of PAO6 on steel with a higher contact angle (θ sp = 21 • ) at 293 K 29 yields a very similar work of adhesion (W sl = 57 mJ m -2 ), which gives further confidence in our target value for the simulations. The higher work of adhesion at the steel/water interface than for steel/PAO4 suggests that the water nanofilm will be thermodynamically stable. The discussion above indicates that the inability of previous force-fields to reproduce the work of adhesion of hematite/PAO4 interfaces 10 based on experimental contact angles 18 could be due to the absence of an interfacial water layer.