| 1. |
- Hansen, Henriette Wase, 1988, et al.
(författare)
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Density scaling of structure and dynamics of an ionic liquid
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:25, s. 14169-14176
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ionic liquids are salts with low melting points achieved by employing bulky and asymmetrical ions. The molecular design leads to apolar and polar parts as well as the presence of competing Coulomb and van der Waals interactions giving rise to nano-scale structure, e.g. charge ordering. In this paper we address the question of how these nano-scale structures influence transport properties and dynamics on different timescales. We apply pressure and temperature as control parameters and investigate the structure factor, charge transport, microscopic alpha relaxation and phonon dynamics in the phase diagram of an ionic liquid. Including viscosity and self diffusion data from literature we find that all the dynamic and transport variables studied follow the same density scaling, i.e. they all depend on the scaling variable Γ = ργ/T, with γ = 2.8. The molecular nearest neighbor structure is found to follow a density scaling identical to that of the dynamics, while this is not the case for the charge ordering, indicating that the charge ordering has little influence on the investigated dynamics.
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| 2. |
- Lundin, Filippa, 1992, et al.
(författare)
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Pressure and Temperature Dependence of Local Structure and Dynamics in an Ionic Liquid
- 2021
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 125:10, s. 2719-2728
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Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the local dynamics in ionic liquids remains an important aspect in the design of new ionic liquids as advanced functional fluids. Here, we use small-angle X-ray scattering and quasi-elastic neutron spectroscopy to investigate the local structure and dynamics in a model ionic liquid as a function of temperature and pressure, with a particular focus on state points (P,T) where the macroscopic dynamics, i.e., conductivity, is the same. Our results suggest that the initial step of ion transport is a confined diffusion process, on the nanosecond timescale, where the motion is restricted by a cage of nearest neighbors. This process is invariant considering timescale, geometry, and the participation ratio, at state points of constant conductivity, i.e., state points of isoconductivity. The connection to the nearest-neighbor structure is underlined by the invariance of the peak in the structure factor corresponding to nearest-neighbor correlations. At shorter timescales, picoseconds, two localized relaxation processes of the cation can be observed, which are not directly linked to ion transport. However, these processes also show invariance at isoconductivity. This points to that the overall energy landscape in ionic liquids responds in the same way to density changes and is mainly governed by the nearest-neighbor interactions.
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