Ionic Liquids: Physics Bridging Two Fields
When considering the ionic liquids (ILs) in general, and especially the room temperature ionic liquids (RTIL), the interest is naturally focused on the ionic conductivity and ion dynamics. Nonetheless, many ionic liquids are glass-formers, and undergo gla
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Ionic Liquids: Physics Bridging Two Fields
7.1
Introduction
When considering the ionic liquids (ILs) in general, and especially the room temperature ionic liquids (RTIL), the interest is naturally focused on the ionic conductivity and ion dynamics. Nonetheless, many ionic liquids are glass-formers, and undergo glass transition at Tg on cooling at ambient pressure or at Pg on elevating the applied pressure at constant temperature. In the supercooled liquid state, both the structural relaxation and the ionic conductivity relaxation are present and observable. Thus glass-forming ILs confer the bonus of studying ionic conductivity relaxation and structural relaxation in the same material. If the two processes are decoupled, the relation between the structural relaxation on the conductivity relaxation and possible effect of the former on the latter is of interest in basic research as well as in applications. Some general and interesting properties of the two relaxation processes are brought out in this chapter. The challenge to theory is the explanation of not only the properties of the conductivity relaxation but also the structural relaxation, and their relations. As it turns out, the properties of the two relaxation processes are similar, in dynamic properties indicating that they stem from some common physics that bridge the two fields. Proposed specifically for ionic conductivity relaxation and diffusion, some theory or model may run into difficulty in adapting it to explain the similar property of structural relaxation and viscosity of glass-formers. This problem casts doubt on the physics of the theory because it is common to the two fields, and should be easy to adapt it to address the other field. Therefore it is beneficial for those engaged in research of ionic conductivity relaxation and particularly in ionic liquids to be aware of the wealth of properties of glass-forming systems and the explanations. The purpose of the following sections is to bring out the general and fundamental properties of ion dynamics that should have great impact on the two research fields. The similarity of the properties in the two fields are made clear by presenting each found in the non-ionic glass-formers to be followed immediately by the same in ionic conductivity relaxation. © Springer International Publishing Switzerland 2017 J. Habasaki et al., Dynamics of Glassy, Crystalline and Liquid Ionic Conductors, Topics in Applied Physics 132, DOI 10.1007/978-3-319-42391-3_7
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7 Ionic Liquids: Physics Bridging Two Fields
Invariance of the Structural α-Dispersion to Various Combinations of T and P with τ α Kept Constant
Studies of changes of relaxation dynamics of glass-formers with temperature at ambient pressure (0.1 MPa) have traditionally been the way to study glass transition. This practice is due largely to experimental convenience in varying temperature. Most of the experimental data of structural α-relaxation in the literature are ambient pressure measurements carried out at different temperatures. From the
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