Character and influence of hydrogen bonding on the microstructures of ionic liquids by means of neutron diffraction and molecular dynamics simulations

在这个项目中，我们希望通过中子衍射(ND)和分子动力学(MD)模拟来研究羟基功能化离子液体(ILS)中氢键的双面性质。在最近的实验研究中，我们已经证明在这个IL家族中，两种不同类型的氢键共存：传统的阳离子和阴离子之间的氢键(Ca)和两个阳离子(Cc)之间的难以捉摸的氢键(Cc)，这两种氢键被认为是由于相似带电离子之间的库仑力而变得更弱。然而，尽管有这样的预期，我们观察到了主体液体和气相中含有氢键阳离子团簇的结构基元。在纯羟基功能化离子液体的初步ND实验中，我们测量了两种类型氢键的距离，结果表明，尽管阳离子之间存在排斥作用，(Cc)HBs比(Ca)HBs短10ppm。羟基官能化ILS中氢键的双面性质使我们可以解决基本问题，我们在这里解决这些问题。首先，将官能化的OH-与非官能化的ILS混合，提供了有关OH-缺陷对ILS中(Ca)和(Cc)团簇的尺寸和分布的影响的信息。其次，将IL与模拟IL阳离子的酒精分子混合，可以通过从离子到ML的转变来研究电荷缺陷时的液体纳米结构。第三，在IL中加入一个竞争OH-基团的强极性质子受体分子，为通过OH-捕捉剂控制Hb的分布开辟了一条途径。根据羟基和电荷缺陷改变氢键团簇的大小和分布，或者引入OH-捕捉剂，可以调节ILS及其混合物的性质，这两个方面都吸引了越来越多的科学和技术兴趣。直接测定法(H…O)和(O…O)键距离，表示羟基功能化离子液体和分子液体中的Hb强度，只能通过ND实验和MD模拟的支持来获得。

In this project, we want to study the double-faced nature of hydrogen bonding in hydroxyl-functionalized ionic liquids (ILs) by means of neutron diffraction (ND) and molecular dynamics (MD) simulations. In recent experimental studies, we have shown that in this IL family, two distinct types of hydrogen bonds (HBs) coexist: The conventional HBs between cation and anion (ca) and elusive HBs between two cations (cc) that are supposed to be much weaker due to the repulsive Coulomb force between the like-charged ions. Despite this expectation, however, we observed structural motifs involving hydrogen-bonded cationic clusters in the bulk liquid and the gas phase. In preliminary ND experiments on pure hydroxyl-functionalized ILs, we have measured the distances for both type hydrogen bonds, showing that the (cc) HBs are 10 ppm shorter than the (ca) HBs despite the repulsive interaction between the cations. The double-faced nature of hydrogen bonding in hydroxyl-functionalized ILs allows tackling fundamental questions, which we address here. Firstly, mixing OH-functionalized with non-functionalized ILs provides information about the influence of OH-defects on the size and distribution of (ca) and (cc) clusters in ILs. Secondly, mixing the IL with alcohol molecules mimicking the IL cation, allows studying the liquid nanostructures upon charge-defects by changing from the ionic to the ML. Thirdly, adding a strong polar proton acceptor molecule competing for the OH-groups in the IL opens a path for controlling the HB distribution by an OH-catcher. Varying the size and distribution of hydrogen bonded clusters upon hydroxyl- and charge-defects or introducing OH-catchers, allows tuning the properties of ILs and their mixtures, which are both attracting increasing interest in science and technology. The direct determination (H…O) and (O…O) bond distances, indicating the HB strengths in hydroxyl-functionalized ionic and molecular liquids, is only accessible through ND experiments and support of MD simulations.