Stability of n -alkanes and n -perfluoroalkanes against horizontal displacement on a graphite surface.

The stability of adsorbed molecules on surfaces is fundamental and important for various applications, such as coating, lubrication, friction, and self-assembled structure formation. In this study, we investigated the structures and interaction energies ( E int ) of propane, n -pentane, n -heptane, perfluoropropane, n -perfluoropentane, and n -perfluoroheptane adsorbed on the surface of C 96 H 24 (a model surface of graphite). The changes in E int (Δ E int = E int - E int (0)) associated with the horizontal displacement from the stable position were calculated using dispersion-corrected density functional theory (DFT; B3LYP-D3), where E int (0) is the E int at the stable position. The maximum value of Δ E int (Δ E int(max) ) associated with the horizontal displacement increased as the chain length increased. The Δ E int(max) for the three n -alkanes were 1.10, 1.82, and 2.35 kcal mol -1 , respectively. The values for n -perfluoroalkanes were 0.57, 0.83, and 1.04 kcal mol -1 , respectively. The Δ E int(max) values for the n -alkanes were significantly larger than those for the corresponding n -perfluoroalkanes. The E int(max) value per carbon atom of the n -alkanes ( ca. 0.30 kcal mol -1 ) is approximately 2.5 times as large as that of n -perfluoroalkanes ( ca. 0.12 kcal mol -1 ). The Δ E int associated with the horizontal displacement of propane and perfluoropropane on circumcoronene (C 54 H 18 ) obtained by the B3LYP-D3 calculations are close to those obtained by the second order Møller-Plesset (MP2) and dispersion-corrected double hybrid DFT calculations, suggesting the sufficient accuracy of the Δ E int obtained by the B3LYP-D3. Thus, our quantitative analysis revealed the higher stability of n -alkanes against horizontal displacement on a graphite surface than that of n -perfluoroalkanes.