The [BMI][Tf2N] Ionic Liquid/Water Binary System: A Molecular Dynamics Study of Phase Separation and of the Liquid-Liquid Interface.

The authors report mol. dynamics (MD) simulations of the aq. interface of the hydrophobic [BMI][Tf2N] ionic liq. (IL), composed of 1-butyl-3-methylimidazolium cations (BMI+) and bis(trifluoromethylsulfonyl)imide anions (Tf2N-). The questions of H2O/IL phase sepn. and properties of the neat interface are addressed, comparing different liq. models (TIP3P vs. TIP5P H2O and +1.0/-1.0 vs. +0.9/-0.9 charged IL ions), the Ewald vs. the reaction field treatments of the long range electrostatics, and different starting conditions. With the different models, the randomly mixed liqs. sep. much more slowly (in 20 to 40 ns) than classical H2O-oil mixts. do (typically, in {\textless}1 ns), finally leading to distinct nanoscopic phases sepd. by an interface, as in simulations which started with a preformed interface, but the IL phase is more humid. The final state of H2O in the IL thus depends on the protocol and relates to IL heterogeneities and viscosity. H2O mainly fluctuates in hydrophilic basins (rich in O(Tf2N) and arom. CH(BMI) groups), sepd. by more hydrophobic domains (rich in CF3(Tf2N) and alkyl(BMI) groups), as monomers and dimers in the weakly humid IL phase, and as higher aggregates when the IL phase is more humid. There is more H2O in the IL than IL in H2O, to different extents, depending on the model. The interface is sharper and narrower (∼10 {\AA}) than with the less hydrophobic [BMI][PF6] IL and is overall neutral, with isotropically oriented mols., as in the bulk phases. The results allow one to better understand the analogies and differences of aq. interfaces with hydrophobic (but hygroscopic) ILs, compared to classical org. liqs. [on SciFinder(R)]

Références

Titre
The [BMI][Tf2N] Ionic Liquid/Water Binary System: A Molecular Dynamics Study of Phase Separation and of the Liquid-Liquid Interface.
Type de publication
Article de revue
Année de publication
2006
Revue
J. Phys. Chem. B
Volume
110
Pagination
13076–13085
ISSN
1520-6106
Soumis le 12 avril 2018