The adsorption of the alkene group provides a significant increase in adsorption strength for GMO (-41.8 kJ mol -1 ) than GMS (-34.2 kJ mol -1 ) on α-Fe 2 O 3 (010) from PAO4. This observation is in agreement with previous experiments of fatty acids on steel surfaces as well as MD simulations of fatty acids on DLC surfaces. The adsorption energy for GMO is slightly larger from branched PAO4 than linear n-hexadecane (-39.0 kJ mol -1 ), which is opposite to the trend observed for SA.