چكيده فارسي :
Quaternary ionic liquids (ILs) based on tetra alkyl ammonium and tetra alkyl phosphonium cations combined with bis(trifluoromethylsulfonyl)imide anion, form hydrophobic ILs, with outstanding physicochemical properties, such as high thermal stability, wide electrochemical window, non-flammability and non-volatility [1].ILs based on these classes of cations have been successfully applied as phase-transfer catalysts, solvents, electrolytes, lubricants and lubricant additives, gas capture agents, coating materials, and chemical sensors [2].Many of these applications require the knowledge of their interfacial behavior, such as wettability and adhesion.Molecular dynamics (MD) simulations method based on classical force fields is a valuable and powerful technique to study solid-liquid interface at an atomistic and molecular level, with the outcome critically comparable with experiments.In this regard, nanodroplets of triethylpentylammoniumbis(trifluoromethylsulfonyl)imide ([N2225]Tf2N) and triethylpentylphosphoniumbis(trifluoromethylsulfonyl)imide ([P2225]Tf2N) ILs were constructed without boundary condition. Four-layered Cu(100) and Cu(111) slabs were constructed in FCC lattice with experimental lattice constant of 3.615 Å.Ionic Liquids droplets were allowed to come into contact with the solid substrates.Equilibration attained after 5ns production run. Periodic boundary conditions were applied in all three directions. All MD simulations were performedusing the DL_POLY program version 2.17 [3]. Energetic contributions and binding energies calculation of ionic nanodroplets on copper surfacesled to the following orderof binding energies: Cu(100)/[N2225]Tf2N Cu(100)/[P2225]Tf2N Cu(111)/[N2225]Tf2N Cu(111)/[P2225]Tf2N.Calculateddensity profiles exhibit pronounced oscillations near the surfaces, implying the layering of molecules. According to the density profiles, orientation of the charged species in all systems near the Cu surfaces follows the order: anion fluorine anion oxygen anion nitrogen cation tail cation head (N or P).Calculated contact angles of both ionic nanodroplets on Cu(100) and Cu(111) surfaces are lower than 90°. This indicates a favorable liquid-surface interaction. Contact angles on Cu(111) surface are lower than those on Cu(100) surface. This may be an indication of the hydrophobicity difference of these two crystallographicallydifferent copper surfaces.
