Autor(es):
Duarte, Pedro 
; Silva, Marcelo ; Rodrigues, Djêide ; Morgado, Pedro ; Martins, Luís F. G. ; Filipe, Eduardo J. M.
Data: 2013
Identificador Persistente: http://hdl.handle.net/10174/9024
Origem: Repositório Científico da Universidade de Évora
Assunto(s): 2,2,2-trifluoroethanol; density; ethanol; hydrogen bonding
Descrição
The effect of mixing hydrogenated and fluorinated molecules that
simultaneously interact through strong hydrogen bonding was investigated: (ethanol +
2,2,2-trifluoroethanol) binary mixtures were studied both experimentally and by
computer simulation. This mixture displays a very complex behavior when compared
with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes.
The excess volumes are large and positive (unlike those of mixtures of hydrogenated
alchools), while the excess enthalpies are large and negative (contrasting with those of
mixtures of alkanes and perfluoroalkanes). In this work, the liquid density of the
mixtures was measured as a function of composition, at several temperatures from
278.15 to 353.15 K and from atmospheric pressure up to 70 MPa. The corresponding
excess molar volumes, compressibilities, and expansivities were calculated over the
whole (p, ρ, T, x) surface. In order to obtain molecular level insight, the behavior of the mixture was also studied by molecular
dynamics simulation, using the OPLS-AA force field. The combined analysis of the experimental and simulation results indicates
that the peculiar phase behavior of this system stems from a balance between the weak dispersion forces between the
hydrogenated and fluorinated groups and a preferential hydrogen bond between ethanol and 2,2,2-trifluoroethanol. Additionally,
it was observed that a 25% reduction of the F−H dispersive interaction in the simulations brings agreement between the
experimental and simulated excess enthalpy but produces no effect in the excess volumes. This reveals that the main reason
causing the volume increase in these systems is not entirely related to the weak dispersive interactions, as it is usually assumed,
and should thus be connected to the repulsive part of the intermolecular potential.
