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Alternative TitleHydrogen Bond of Ionic Liquid and Its Influence on Properties
Thesis Advisor张锁江
Degree Grantor中国科学院研究生院
Degree Discipline应用化学
Keyword离子液体   氢键网络   性质   应用
Abstract本论文以建立定量的离子液体结构-性质构效关系为切入点,结合模拟和实验,从结构、性质和应用等几个不同方面,重点阐明和揭示了离子液体中广泛存在的氢键及其网络结构,以及其对离子液体一些重要性质的影响规律,旨在为建立定量预测模型、设计功能化离子液体提供科学的依据和理论指导。主要研究内容概括总结如下: (1) 结构方面,采用从头计算密度泛函(DFT)方法,从几何结构、相互作用能、电荷转移和前线分子轨道对典型离子对([Emim][BF4]和[Bmim][PF6])进行了剖析,发现阴阳离子间形成氢键,但由于静电力的耦合强化,使得这种氢键作用具有共价键特征。结合远红外(Far-IR)光谱,发现多个离子能扩展形成氢键网络结构, 表现为液态下离子的局部结构特征。 (2) 性质方面,以不同大小离子簇为液态结构,以单个离子、离子对和中性分子为气相结构,采用统计热力学“簇”的方法,计算了典型的非质子和质子型离子液体的蒸发焓,通过和实验的蒸发焓比较,结合原位红外光谱(in-situ IR),分析了离子液体气相结构,发现其气相组成主要为离子对和通过质子转移的中性分子。进一步研究发现氢键对离子液体蒸发焓的影响不能忽略,但和常规溶剂相反,氢键使离子液体的蒸发焓有降低的趋势。 (3) 应用方面,研究了离子液体分离天然活性同系物的机理。采用从头计算DFT方法和分子动力学(MD)模拟,以三种大豆异黄酮苷元同系物为模型化合物,通过分析阴阳离子和同系物的相互作用能、NBO轨道、氢键临界点的密度以及径向分布函数(RDF)等发现,离子液体能与同系物的形成不同的氢键作用是主要的识别驱动力。 (4) 采用非平衡态MD模拟,研究了离子液体和水的相互作用机理和动态的相转移 过程。选择[Bmim]Cl、[Bmim][BF4]和[Bmim][PF6] 三种截然不同溶解度的离子液体为模型化合物,计算了其在水中扩散时间和离子分布状态,发现亲水性离子液体在水中的扩散速度远快于疏水性离子液体,且容易形成小的离子簇。从计算的阴离子、阳离子以及离子对从离子相迁移到水相的平均力势能(PMF),发现亲水性离子液体离子迁移的PMF降低,说明离子溶解是自由能减少的过程,能自发进行,而疏水性离子液体离子迁移的PMF升高,说明离子溶解是自由能增加过程,非自发进行。进一步研究了离子液体-水界面的结构,发现亲水性和疏水性离子液体阳离子在界面处的取向有很大不同,阳离子倾向于垂直亲水性界面,呈片状分布,水分子容易渗入体相中,而阳离子倾向于平行疏水性界面,形成了一种亚稳定结构,水很难打破这种结构进入体相,导致和水的不溶解。
Other AbstractWith unique properties, ionic liquids (ILs) have arisen the strong interests in academic and industrial communities. In this work, combining computations and expriments, we investigated the relationship between structures and properties of the typical ILs, and mainly discussed the hydrogen bonds (H-bonds) and networks and its effects on the important properties. The aim is to underline in building the empirical models and designing funcational ILs. The detail contents and innovations are listed as follows. (1) The geometries, interaction energies, charge transfer and frontier MOs of [Emim][BF4] and [Bmim][PF6] ion pairs were calculated by DFT at B3LYP/6-31++G** level, and H-bonds are found to be structural feature between anion and cation. Due to the electrostatic coupling, the H-bonds showed the co-valent feature. Combining the far-IR spectra, the H-bonded network forms among ions, which shows the ionic arrangement in liquid phase. (2) The vapoured enthalpies of aprotic and protic ILs were calculated by statistical thermodynamic cluster method when the gas phases were assumed to the different species. Combining the in-situ IR, the structures in gas phase were discussed, and the pairwared ions and the neutral molecues by proton transfer are possible species. It is also found that the H-bonds decreased enthalpies of vapourization, which showed conversed effects with the traditional solvants. (3) In applications, three soybean isoflavone aglycones as model compounds, the mechanism of separating the natural bioactive homologues using ILs was investigated.The interaction energies, NBO orbitals, densities of H-bond critical point and RDF were calculated by DFT and MD simulation, and it is found that anion and cation can form the different H-bonds with the phenolic hydroxyl groups on the three aglycones, which is the main driving force to recognize and separate them. (4) The interactions and dynamic phase change between [Bmim]Cl, [Bmim][BF4] and [Bmim][PF6] ILs and water were intestigated by the non-equilibrium MD simulation, which is very important in some applications of ILs, but isnot yet addressed clearly. Phase dispersion of ILs into water phase and ionic aggragate in water were calculated, the dispersion time hydrophilic [Bmim]Cl IL is shorter than hydrophobic [Bmim][PF6] IL, and small ionic clusters were found in the mixture of hydrophilic [Bmim]Cl IL and water. Moreover, the PMF of thransferring anion, cation and ion pair from ILs phase to water phase were calculated, and PMF of the species of hydrophilic IL decreases, which indicates the transferring is spontaneous. But PMF of hydrophobic IL increases, which indicates the transferring is not spontaneous. The interface ofIL-water is critical to understand the solubility, and the results indicated that the arrangement of cations at interface of hydrophilic and hydrophobic ILs is very different. The cations are perpendicular to the interface and form the schistose structure in hydrophilic IL, and water molecules are easy to penetrate the bulk phase. However, The cations are parallel with the interface in hydrophobic IL, and water molecules are difficult to break the H-bonded network to penetrate the bulk phase.
Document Type学位论文
Recommended Citation
GB/T 7714
董坤. 离子液体氢键及其对物化性质的影响[D]. 中国科学院研究生院,2013.
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