Comparing Figure to Figure shows that the adsorption is slightly weaker from n-hexadecane than from iso-octane. The oscillatory mass density profiles in Figure show stronger layering on circumovalene for the long linear alkane n-hexadecane than the shorter branched alkane iso-octane. This observation is in agreement with previous MD simulations of linear and branched alkanes. The density oscillations in Figure extends further into the bulk for n-hexadecane (∼ 30 Å) compared to iso-octane (∼ 20 Å). Moreover, the peaks in the density profile are more pronounced with respect to the bulk baseline as chain-like molecules tend to align parallel to the deposit. This stronger layering provides additional barriers to adsorption, since binding onto the surface requires the surfactant molecules to penetrate through these layers and partially remove alkane molecules. In Figure , the most stable adsorption structure in the PMF occurs at similar head-group-PAH distances (between 3 and 6 Å) for both surfactants. These distances are in good agreement with previous MD simulations of small molecule adsorption on graphene from water. Unlike those for small molecules, the PMFs for the larger surfactants of this study do not show a single sharp basin, but have the broad main feature at ∼ 4 Å and a less apparent shoulder at ∼ 6 Å. The position of the main basin corresponds to that of the first solvent mass density maximum in Figure , suggesting that the surfactants need to penetrate the final strongly-layered solvent layer to maximise the adsorption strength.