Ionic liquids: dissecting the enthalpies of vaporization.
We calculate the heats of vaporisation for imidazolium-based ionic liquids [C(n)mim][NTf(2)] with n=1, 2, 4, 6, 8 by means of molecular dynamics (MD) simulations and discuss their behavior with respect to temperature and the alkyl chain length. We use a force field developed recently. The different cohesive energies contributing to the overall heats of vaporisations are discussed in detail. With increasing alkyl chain length, the Coulomb contribution to the heat of vaporisation remains constant at around 80 kJ mol(-1), whereas the van der Waals interaction increases continuously. The calculated increase of about 4.7 kJ mol(-1) per CH(2)-group of the van der Waals contribution in the ionic liquid exactly coincides with the increase in the heats of vaporisation for n-alcohols and n-alkanes, respectively. The results support the importance of van der Waals interactions even in systems completely composed of ions.
Köddermann
Thorsten
T
Institut für Chemie, Abteilung Physikalische Chemie, Universität Rostock, Dr.-Lorenz-Weg 1, 18059 Rostock, Germany.
Paschek
Dietmar
D
Ludwig
Ralf
R
D003198:Computer Simulation; D006358:Hot Temperature; D057927:Hydrophobic and Hydrophilic Interactions; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D008956:Models, Chemical; D013696:Temperature; D013816:Thermodynamics; D014835:Volatilization
D007093:Imidazoles; D052578:Ionic Liquids