n-Dodecane Evaporation/Condensation: A Comparative Quantum Chemical Study

The effects of temperature and conformerisation on the evaporation/condensation coefficient (beta) and the evaporation rate (gama) for n-dodecane nano and micro-droplets are analysed using quantum chemical DFT calculations for several ensembles of conformers of n-dodecane molecules in the gas and liquid phases. To highlight the underlying physics of the evaporation/condensation process, the internal molecular dynamics (IMD) effects of n-dodecane molecules on heat transfers between gas and liquid phases are investigated. Bond energies, the Gibbs free energies of internal dynamics of a set of n-dodecane conformers, and the energies of the molecules colliding with the surface of an n-dodecane nanodroplet are studied using the quantum chemical approach. The values of "gama" and "beta" are shown to be sensitive to the changes in the Gibbs free energy (G) of conformers in the gas and liquid phases. The values of G referring to internal dynamics in n-dodecane conformers are estimated using the quantum continuum solvent model, ωB97X-D/cc-pVTZ chemistry electronic model and programs Gaussian 09, CP2K and MSTor in which conformational, torsional and vibrational effects are taken into account. Conformerisation effects leading to a decrease in "gama" cause an increase in the evaporation rate and decrease in the evaporation time compared with those computed without consideration of these effects. The latter are attributed to anharmonicity effects inferred from the coupling of vibrational, rotational, torsional and conformational dynamics. This coupling leads to favourable changes in the Gibbs free energy of evaporation of certain conformers during their transfer from the liquid into the gas phase. Without consideration of these effects, the evaporation rate can be underestimated by up to an order of magnitude