For the hydrocarbon solvent, n-hexadecane was compared to hydrogenated 1-decene trimer. While n-hexadecane is commonly used as a model base oil in adsorption and boundary friction experiments, 24,25 hydrogenated 1-decene trimer is the primary constituent of commercial PAO4 base oil, a poly-α-olefin with a kinematic viscosity of 4 cSt at 100 °C. The molecular structures of the base oils are shown in Fig. .