Self assembly, dynamics and charge transport in bulk ionic liquids and ionogels

离子液体(ILS)，即在室温下呈液态的熔盐，是一种具有特殊性质的液体，具有许多潜在的应用，例如在所谓的“绿色化学”或能源应用中。许多离子液体由于其两亲性的分子结构，往往在介观尺度上表现出自组装和结构形成(即形成极区和非极区)，这影响了分子动力学和离子在这些材料中的传输。本项目的目的是了解电荷输运和分子动力学如何依赖于离子液体的介观结构，特别是这些体系中电荷输运和结构弛豫的耦合/去耦合现象。因此，在本项目中，我们研究了一系列具有不同倾向形成极性/非极性域的离子液体(例如，通过改变阳离子的烷基链长或通过添加少量溶剂来实现)。下一步计划研究离子凝胶中的离子液体。后一种体系是以离子液体为基础，加入各种网络形成剂。在这些材料中，高导电性通常与几乎固体一样的机械性能相结合，这使得它们在许多应用中特别有趣。在离子凝胶中，内表面对IL结构的形成以及对动力学和电荷传输的影响有待阐明。特别是，当网络形成剂的几何构型的长度尺度与IL中的结构域和聚集体的长度尺度相匹配时，可以预期有趣的效果。在实验方法上，本项目的重点是去偏振动态光散射，它明确地识别分子的重定向，不受电荷输运或偏振效应的影响。不同的光散射技术(光子相关、串联法布里·珀罗和拉曼光谱)的组合使我们能够覆盖从1 MHz到大约10 THz的全部相关光谱范围。同时，宽带介电光谱学(1微赫兹和50 GHz之间)将提供有关系统中电荷传输的信息。这样，就有可能明确地将分子动力学和电荷传输分开。利用小角散射技术对离子液体中随温度变化的磁畴结构进行监测。因此，我们希望加深对离子液体和离子凝胶中结构形成、动力学和电荷输运之间相互关系的理解，这将有助于实现基于知识的离子液体材料设计。

Ionic Liquids (ILs), i.e. molten salts that are liquid at room temperature, are liquids with unusual properties that have many potential applications, e.g. in what is known as "green chemistry" or in energy applications. Many ionic liquids, due to their amphiphilic molecular architecture, tend to show self-assembly and structure formation on the mesoscale (i.e. formation of polar and apolar domains), which influences molecular dynamics and ion transport in these materials. It is the aim of the current project to understand, how charge transport and molecular dynamics depend on the ionic liquid mesostructure, with particular emphasis on coupling/decoupling phenomena of charge transport and structural relaxation in these systems.Therefore in this project a series of Ils with varying tendency to form polar/apolar domains is investigated (realized, e.g. by varying the alkyl chain length of a cation or by addition of small amounts of solvents) with respect to molecular dynamics and ion transport. In the next step it is planned to investigate Ils in ionogels. The latter systems are based on ionic liquids by adding various network forming agents. In these materials high conductivity is often combined with almost solid-like mechanical properties, which makes them particularly interesting for many applications. In the ionogels the effect of inner surfaces on the IL structure formation and on dynamics and charge transport are to be clarified. In particular, interesing effects are expected when the length scale of geometric confnement by the network forming agent meets the lengthscale of domains and aggregates in the IL. In terms of experimental method, the emphasis in the current project is on depolarized dynamic light scattering, which unambiguously identifies molecular reorientation and is not influenced by charge transport or polarization effects. A combination of different light scattering techniques (photon correlation, Tandem Fabry Perot and Raman spectroscopy) allows us to cover the full relevant spectral range, between 1 mHz up to about 10 THz. At the same time broadband dielectric spectroscopy (between 1 Microherz and 50 GHz) will provide information on the charge transport in the system. In that way it will be possible to unambiguously separate molecular dynamics and charge transport. The temperature dependent domain structure in the ILs will be monitored by small angle scattering techniques. Therefore, we expect to improve our understanding of the interrelation of structure formation, dynamics and charge transport in ILs and in ionogels, which, on the long run, will help to realize knowledge-based material design with ionic liquids.