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Using Molecular Simulation to Understand the Structure of [C2C1im]+–Alkylsulfate Ionic Liquids: Bulk and Liquid–Vapor Interfaces
journal contribution
posted on 2012-12-06, 00:00 authored by Xavier Paredes, Josefa Fernández, Agílio A. H. Pádua, Patrice Malfreyt, Friedrich Malberg, Barbara Kirchner, Alfonso Sanmartín PensadoUsing molecular dynamics simulations
we have studied the structure
of alkylsulfate-based ionic liquids: 1-ethyl-3-methylimidazolium n-alkylsulfate [C2C1im][CnSO4] (n = 2, 4, 6 and
8). The structure of the different ionic liquids have been interpreted
taking into account radial and spatial distribution functions, and
structure factors, that allowed us to characterize the morphology
of the polar and nonpolar domains present in this family of liquids.
The size of the nonpolar regions depends linearly on the anion alkyl
chain length. Furthermore, properties of the surface of ionic liquids,
such as surface tension, ordering, and charge and density profiles,
were studied using molecular simulation. We were able to reproduce
the experimental values of the surface tension with a maximum deviation
of 10%, and it was possible to relate the values of the surface tension
with the structure of the liquid–vacuum interfaces. Microscopic
structural analysis of orientational ordering at the interface and
density profiles along the direction normal to the interface suggest
that the alkyl chains of the anions tend to protrude toward the vacuum,
and the presence of the interface leads to a strong organization of
the liquid phase in the region close to the interface, stronger when
the side-chain length of the anions increases.