The adsorption strength decreases with decreasing deposit size, which is due to the reduced number of potential binding sites for the DCA. For the smaller coronene deposit, the PIBSI PMF becomes almost flat, with only a shallow energy minimum of -0.7 kcal mol -1 , as shown in Figure . Adsorption is somewhat stronger for hexa-cata-benzocoronene with an energy minimum of -1.3 kcal mol -1 for PIBSI, as shown in Figure . The reason for these very small values is due to the PIBSI head-group being larger than the deposit and not sufficiently flexible to maximise the number of non-covalent interactions with the PAH edge when wrapping around it. The energy minima for the smaller PAHs are at larger distances than for circumovalene, with the minima in the free energy profiles at ξ ≈ 6 Å. This suggests that the optimal adsorption conformation occurs when the DCA head-group lies directly on top of the deposit, and that the conformations with the DCA wrapped around the deposit are not as favourable. A similar trend is found for the zwitterionic surfactant, but with much stronger adsorption. The free energy of adsorption is slightly stronger when interacting with C 48 H 24 (-5.0 kcal mol -1 ) than with C 24 H 12 (-4.3 kcal mol -1 ), highlighting once again the role played by the number of deposit binding sites.