The experimental HFRR results are obtained calculating the steady-state friction coefficient from three repetitions of the HFRR experiments at each OFM concentration. The results for GMO and GMS are shown in Figure . The highest friction coefficient (0.263) is observed for the pure base oil (not depicted in Figure ). As expected, the lowest friction coefficient is observed for the highest OFM concentrations, corresponding to 0.02 M for GMO (0.0103 in molar fraction) or 0.01 M for GMS (0.005 in molar fraction). These concentrations correspond to the high coverage regime according to the calculated MTT adsorption isotherms (see Fig. ), with 2-3 nm -2 . This is in contrast to the results of Jaishankar et al. for SA.