Quasielastic Neutron Scattering Investigations of Ionic Liquids and Comparison to Complementary Methods

在瑞士维利根paul - scherrer研究所的瑞士散裂源SINQ上，利用我们自己的冷中子飞行时间光谱仪FOCUS，我们将系统地进行一系列准弹性中子散射（QENS）实验，以阐明离子液体在空间和时间原子尺度上的动力学。我们建议用不同烷基链的[n -烷基- n -甲基吡咯烷]双（三氟甲基磺酰基）亚胺作为模型体系。由于质子是主要的散射中心，QENS在这些系统上探测阳离子动力学。从文献中得知，并通过QENS测试实验证实，阳离子侧链中的氢原子进行局域旋转运动。为了研究扩散动力学，必须对这些侧链进行氘化，这样才能观察到刚性阳离子主链上的氢原子。从与模型无关的数据评估出发，我们将首先设想动力学的基本特征。然后，将根据适当的理论模型进行数据评估，例如双态模型，该模型可以深入了解离子对形成的动力学。为了区分非相干和相干QENS，从而区分单粒子扩散和集体扩散，在后期还打算使用偏振中子和中子偏振分析的QENS。

Using our own cold neutron time-of-flight spectrometer FOCUS at the Swiss spallation source SINQ of the Paul-Scherrer-lnstitute in Villigen (Switzerland) we would like to perform systematically a series of quasielastic neutron scattering (QENS) experiments to elucidate the dynamics in ionic liquids on atomistic scales of space and time. As model system we suggest [N-alkyl-N-methyl-pyrrolidinium] bis-(trifluoromethylsulfonyl) imide with different alkyl chains. Since protons are the dominant scattering centers, QENS on these systems probes the cation dynamics. It is known from literature, and confirmed by a QENS test experiments, that the hydrogen atoms in the cation side chains perform localized rotational motions. In order to study the diffusional dynamics these side chains have to be deuterated, so the hydrogen atoms at the stiff cation backbone can be observed. From model-independent data evaluation the essential features of the dynamics will first be conceived. Afterwards the data evaluation will be done in terms of appropriate theoretical models, for instance the two-state-model, which could give insight into the kinetics of ion pair formation. At a later stage also QENS with polarized neutron and neutron polarization analysis is intended in order to distinguish between incoherent and coherent QENS and thus between single particle diffusion and collective diffusion.