Interactions within a [ionic liquid + poly(ethylene glycol)] mixture revealed by temperature-dependent synergistic dynamic viscosity and probe-reported microviscosity.
Interactions within a [ionic liquid + poly(ethylene glycol)] mixture revealed by temperature-dependent synergistic dynamic viscosity and probe-reported microviscosity.
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DOI：
10.1021/jp203079p
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发表时间：
2011-05
期刊：
影响因子：
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通讯作者：
S. Trivedi;S. Pandey
中科院分区：
文献类型：
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作者：
S. Trivedi;S. Pandey
离子液体（IL）与聚乙二醇（PEG）的混合物可以提供具有有利性质的介质。常见和流行的IL 1-丁基-3-甲基咪唑六氟磷酸盐混合物的动态粘度（[bmim][PF（6）]）与平均分子量（MW）200（PEG 200）、平均MW 400（PEG 400）、数均MW M（n）570-630（PEG 600）的PEG，和数均MW M（n）950-1050（PEG 1000）。动态粘度的温度依赖性表明（[bmim][PF（6）] + PEG）混合物表现为牛顿流体，并发现遵循Arrhenius型行为。在IL-丰富的区域，（[bmim][PF（6）] + PEG 200）混合物的过量对数粘度被发现是负的和独立的温度。（[bmim][PF（6）] + PEG 600）和（[bmim][PF（6）] + PEG 1000）的混合物显示出罕见的和不寻常的粘度“协同作用”或“高粘度”，即观察到混合物粘度显著高于形成混合物的两种纯组分的粘度，产生大的正过量对数粘度。这些正的过量对数粘度随着温度的升高而降低。IL和PEG之间形成广泛的氢键不仅补偿了[bmim][PF（6）]和PEG 600/PEG 1000内库仑吸引力和货车范德华相互作用的损失，还产生了粘度协同作用。这种补偿对于（[bmim][PF（6）] + PEG 200）和（[bmim][PF（6）] + PEG 400）混合物是不够的。FTIR吸光度数据提供了混合物中氢键的证据。用微流动性探针1，3-双（1-芘基）丙烷（BPP）的分子内激基缔合物荧光强度比与分子内激基缔合物荧光寿命的乘积来反映混合物在不同温度下的微粘度。微粘度在所有四种（[bmim][PF（6）] + PEG）混合物中显示出协同效应。氢键对微粘度的贡献大于库仑和货车德瓦耳斯相互作用。（[bmim][PF（6）] + PEG）混合物的动态粘度和微粘度的协同作用是分子间和分子内氢键以及库仑和货车德瓦尔斯型相互作用的复杂相互作用。
Mixtures of ionic liquid (IL) with poly(ethylene glycol) (PEG) may afford media with favorable properties. Dynamic viscosities of mixtures of a common and popular IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) with PEGs of average molecular weight (MW) 200 (PEG200), average MW 400 (PEG400), number-average MW M(n) 570-630 (PEG600), and number-average MW M(n) 950-1050 (PEG1000) over a complete composition range at 10° intervals in the temperature range of 10-90 °C are measured. The temperature dependence of the dynamic viscosity shows ([bmim][PF(6)] + PEG) mixtures to behave as Newtonian fluids and is found to follow Arrhenius-type behavior. In the IL-rich region, excess logarithmic viscosities for the ([bmim][PF(6)] + PEG200) mixture are found to be negative and independent of the temperature. Mixtures of ([bmim][PF(6)] + PEG600) and ([bmim][PF(6)] + PEG1000) show rare and unusual viscosity "synergism" or "hyperviscosity" in the sense that the mixture viscosity is observed to be significantly higher than the viscosity of both the neat components forming the mixture, giving rise to large positive excess logarithmic viscosities. These positive excess logarithmic viscosities decrease with increasing temperature. Formation of extensive H-bonding between the IL and PEG more than compensates for the losses in Coulombic attractive and van der Waals interactions within [bmim][PF(6)] and PEG600/PEG1000, respectively, giving rise to viscosity synergism. This compensation is not enough for ([bmim][PF(6)] + PEG200) and ([bmim][PF(6)] + PEG400) mixtures. The evidence for H-bonding in the mixtures is provided by FTIR absorbance data. The product of the monomer-to-excimer emission intensity ratio and the lifetime of the intramolecular excimer fluorescence of a microfluidity probe, 1,3-bis(1-pyrenyl)propane (BPP), is used as a reflection of the microviscosity of the mixture at different temperatures. The microviscosity shows synergistic effects in all four ([bmim][PF(6)] + PEG) mixtures. The contribution of H-bonding to the microviscosity reported by BPP is observed to be more then that as compared to contributions of Coulombic and van der Waals interactions. Synergism in the dynamic viscosity and microviscosity of ([bmim][PF(6)] + PEG) mixtures is a complex interplay of inter- and intramolecular H-bonding as well as Coulombic and van der Waals type interactions.