Using Molecular Simulation to Understand the Structure of [C2C1im]+鈥揂lkylsulfate Ionic Liquids: Bulk and Liquid鈥揤apor Interfaces

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• 作者：Xavier Paredes ; Josefa Fern谩ndez ; Ag铆lio A. H. P谩dua ; Patrice Malfreyt ; Friedrich Malberg ; Barbara Kirchner ; Alfonso Sanmart铆n Pensado
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：December 6, 2012
• 年：2012
• 卷：116
• 期：48
• 页码：14159-14170
• 全文大小：875K
• 年卷期：v.116,no.48(December 6, 2012)
• ISSN：1520-5207

文摘

Using molecular dynamics simulations we have studied the structure of alkylsulfate-based ionic liquids: 1-ethyl-3-methylimidazolium n-alkylsulfate [C₂C₁im][C_nSO₄] (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鈥搗acuum 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.