Burankova Tatsiana, Mora Cardozo Juan F, Rauber Daniel, Wildes Andrew, Embs Jan P
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, 5232, Villigen, PSI, Switzerland.
Department of Physical Chemistry, Saarland University, 66123, Saarbrücken, Germany.
Sci Rep. 2018 Nov 6;8(1):16400. doi: 10.1038/s41598-018-34481-w.
Coupling between dynamical heterogeneity of ionic liquids and their structural periodicity on different length-scales can be directly probed by quasielastic neutron scattering with polarization analysis. The technique provides the tools to investigate single-particle and cooperative ion motions separately and, thus, dynamics of ion associations affecting the net charge transport can be experimentally explored. The focus of this study is the structure-dynamic relationship in the protic ionic liquid, triethylammonium triflate, characterized by strong hydrogen bonds between cations and anions. The site-selective deuterium/hydrogen-isotope substitution was applied to modulate the relative contributions of different atom groups to the total coherent and incoherent scattering signal. This approach in combination with molecular dynamics simulations allowed us to obtain a sophisticated description of cation self-diffusion and confined ion pair dynamics from the incoherent spectral component by using the acidic proton as a tagged particle. The coherent contribution of the neutron spectra demonstrated substantial ion association leading to collective ion migration that preserves charge alteration on picosecond time scale, as well as correlation of the localized dynamics occurring between adjacent ions.
通过带有偏振分析的准弹性中子散射，可以直接探测离子液体动力学非均匀性与其在不同长度尺度上的结构周期性之间的耦合。该技术提供了分别研究单粒子和协同离子运动的工具，因此，可以通过实验探索影响净电荷传输的离子缔合动力学。本研究的重点是质子离子液体三乙胺三氟甲磺酸盐中的结构 - 动力学关系，其特征是阳离子和阴离子之间存在强氢键。采用位点选择性氘/氢同位素取代来调节不同原子基团对总相干和非相干散射信号的相对贡献。这种方法与分子动力学模拟相结合，使我们能够通过使用酸性质子作为标记粒子，从不相干光谱分量中获得阳离子自扩散和受限离子对动力学的精细描述。中子光谱的相干贡献表明存在大量离子缔合，导致集体离子迁移，这种迁移在皮秒时间尺度上保持电荷变化，以及相邻离子之间发生的局部动力学相关性。
