Monte Carlo simulations of water solubility in ionic liquids: A force field assessment

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• 作者：Eliseo Marin-Rimoldi^a ; Jindal K. Shah^b ; Edward J. Maginn^a ; ^{ed@nd.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Ionic liquids ; Water solubility ; Monte Carlo ; Force field ; Absorption ; Gibbs ensemble
• 刊名：Fluid Phase Equilibria
• 出版年：2016
• 出版时间：15 January 2016
• 年：2016
• 卷：407
• 期：Complete
• 页码：117-125
• 全文大小：852 K

文摘

Gibbs ensemble Monte Carlo simulations were used to calculate absorption isotherms of water in three imidazolium-based ionic liquids (ILs) with different degrees of hydrophobicity: 1-m>nm>-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]), 1-m>nm>-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C₄mim][Tf2N]) and 1-m>nm>-butyl-3-methylimidazolium chloride ([C₄mim][Cl]). An evaluation of several water models and various IL force fields was conducted. The selected water models are the TIP5P, TIP4P2005 and a collection of three site models based on the SPC geometry but with different sets of fixed partial charges. These partial charges are consistent with water surrounded by different electrostatic environments, and crudely account for polarizability. In the case of the IL force fields, net partial charges of ±1.0e were used. In addition, scaled charges of ±0.9e and ±0.8e were used to account for polarization and charge transfer. It is found that most water models tested with the full charge [C₄mim][PF₆] and [C₄mim][Cl] force field overestimate the solubility, but the agreement is reasonably good with [C₄mim][Tf2N]. Attempts at improving the results by either scaling the charges on the IL or on water were made, but no combination was able to reproduce experimental phase behavior satisfactorily. The main conclusion of the study is that, to consistently model water absorption in ILs, force fields that include effects such as polarization are likely necessary.