Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic-Liquid Mixtures.
Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic-Liquid Mixtures.
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DOI：
10.1021/acs.jpcb.1c10460
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发表时间：
2022-03-10
影响因子：
3.3
通讯作者：
McKendrick, Kenneth G.
中科院分区：
文献类型：
--
作者：
Purcell, Simon M.;Lane, Paul D.;D'Andrea, Lucia;Elstone, Naomi S.;Bruce, Duncan W.;Slattery, John M.;Smoll, Eric J., Jr.;Greaves, Stuart J.;Costen, Matthew L.;Minton, Timothy K.;McKendrick, Kenneth G.
离子液体的气-液界面在许多应用中至关重要，例如在负载离子液体相（SILP）催化中。研究这些体系中界面结构的方法将使其性能得到合理的改善。在这项研究中，反应原子散射（RAS），表面张力测量和分子动力学（MD）模拟被用来研究部分氟化和正常的烷基离子液体的混合物的真空界面。其根本目的是了解氟化离子液体是否可以用作添加剂，以修改表面结构的一个最广泛使用的家庭的烷基离子液体。1-烷基-3-甲基咪唑双离子液体系列三氟甲磺酰亚胺（[Cnmim][Tf 2N]）（n = 4-12）与固定长度的半全氟化类似物混合（1H，1H，2 H，2 H-全氟辛基）-3-甲基咪唑鎓双三氟甲磺酰亚胺（[C8 mimF 13][Tf 2N]），形成[Cnmim]（1-x）[C8 mimF 13]x[Tf 2N]混合物，其中x是氟化组分的本体摩尔分数。RAS-LIF方法将O原子射弹与产物OH的激光诱导荧光（LIF）检测相结合，作为烷基链表面暴露的量度。对于[C8 mim]（1-x）[C8 mimF 13]x[Tf 2N]混合物，RAS-LIF OH产率低于根据化学计量预期的产率。表面张力的线性存在定量一致的负偏差。这两个结果都意味着较低表面张力的氟烷基材料占主导地位的表面。一个类似的赤字被发现为烷基链长度n = 4，6，8，和12和所有（非零）x RAS-LIF调查。[Cnmim]（1-x）[C8 mimF 13]x[Tf 2N]混合物的MD模拟的可吸收表面积（阿萨）分析定性地再现了在n的大部分范围内表面的氟链优势的相同主要效应。然而，有显着的定量差异之间的MD阿萨的预测和实验有关的强度的任何n-依赖的相对烷基覆盖率在固定的x，并在固定的n的x-依赖。这些差异进行了讨论的背景下，在MD模拟预测的表面结构的详细检查。潜在的解释，除了实验文物，包括在MD模拟中使用的经典力场的不足之处，或简单的阿萨算法无法捕捉影响RAS-LIF产量的动力学因素。
The gas–liquid interface of ionic liquids (ILs) is critically important in many applications, for example, in supported IL phase (SILP) catalysis. Methods to investigate the interfacial structure in these systems will allow their performance to be improved in a rational way. In this study, reactive-atom scattering (RAS), surface tension measurements, and molecular dynamics (MD) simulations were used to study the vacuum interface of mixtures of partially fluorinated and normal alkyl ILs. The underlying aim was to understand whether fluorinated IL ions could be used as additives to modify the surface structure of one of the most widely used families of alkyl ILs. The series of ILs 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][Tf2N]) with n = 4–12 were mixed with a fixed-length, semiperfluorinated analogue (1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C8mimF13][Tf2N]), forming [Cnmim](1–x)[C8mimF13]x[Tf2N] mixtures, where x is the bulk mole fraction of the fluorinated component. The RAS-LIF method combined O-atom projectiles with laser-induced fluorescence (LIF) detection of the product OH as a measure of surface exposure of the alkyl chains. For [C8mim](1–x)[C8mimF13]x[Tf2N] mixtures, RAS-LIF OH yields are below those expected from stoichiometry. There are quantitatively consistent negative deviations from linearity of the surface tension. Both results imply that the lower-surface-tension fluoroalkyl material dominates the surface. A similar deficit is found for alkyl chain lengths n = 4, 6, 8, and 12 and for all (nonzero) x investigated by RAS-LIF. Accessible-surface-area (ASA) analyses of the MD simulations for [Cnmim](1–x)[C8mimF13]x[Tf2N] mixtures qualitatively reproduce the same primary effect of fluoro-chain predominance of the surface over most of the range of n. However, there are significant quantitative discrepancies between MD ASA predictions and experiment relating to the strength of any n-dependence of the relative alkyl coverage at fixed x, and on the x-dependence at fixed n. These discrepancies are discussed in the context of detailed examinations of the surface structures predicted in the MD simulations. Potential explanations, beyond experimental artifacts, include inadequacies in the classical force fields used in the MD simulations or the inability of simple ASA algorithms to capture dynamical factors that influence RAS-LIF yields.
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影响因子：
3.3
作者：
Baker, RP;Costen, ML;Summerdeld, D
通讯作者：
Summerdeld, D
影响因子：
--
作者：
BONDI, A
通讯作者：
BONDI, A
影响因子：
4.3
作者：
Heller, Bettina S. J.;Lexow, Matthias;Steinrueck, Hans-Peter
通讯作者：
Steinrueck, Hans-Peter
影响因子：
3
作者：
EISENHABER, F;LIJNZAAD, P;SCHARF, M
通讯作者：
SCHARF, M
影响因子：
3.9
作者：
Bowers, J;Vergara-Gutierrez, MC;Webster, JRP
通讯作者：
Webster, JRP