In this chapter we will review the capabilities of X-Ray diffraction experiments in the field of ionic liquids, carried out with the Energy Dispersive variant of the technique. Besides its widespread use in the determination of solid (crystal) structure, in fact, X-Ray diffraction can also be conveniently used to obtain information about the liquid” structure. After the description of data collection and treatment, and a small review of the underlying theory, we will show several examples of the structure factors and the radial distribution functions that can be obtained from dif fraction patterns. These two quantities can be considered as a fingerprint of the ionic liquid, and depend intimately upon the relative disposition of the ions in the liquid phase. Among the most noteworthy spectral features that can be pointed out, we will discuss those deriving from hydrogen-bond interactions, as well as the First Sharp Diffraction Peak (FSDP) that highlight the presence of medium range order (MRO) in the liquid. We will describe several measurements on the protic IL butylammonium nitrate and its water mixtures at different molar fractions, where both features can be found, and show how EDXD patterns can account for the modulation of these features with the composition. In the end, we will show how the change of FSDP spectral feature that occurs during the fusion of alky- lammonium chlorides can be tracked with a multiangular ADXD Rietveld diffrac- tometer.
X-Ray Diffraction Studies of Ionic Liquids: from Spectra to Structure and Back
GONTRANI, LORENZO;
2013-01-01
Abstract
In this chapter we will review the capabilities of X-Ray diffraction experiments in the field of ionic liquids, carried out with the Energy Dispersive variant of the technique. Besides its widespread use in the determination of solid (crystal) structure, in fact, X-Ray diffraction can also be conveniently used to obtain information about the liquid” structure. After the description of data collection and treatment, and a small review of the underlying theory, we will show several examples of the structure factors and the radial distribution functions that can be obtained from dif fraction patterns. These two quantities can be considered as a fingerprint of the ionic liquid, and depend intimately upon the relative disposition of the ions in the liquid phase. Among the most noteworthy spectral features that can be pointed out, we will discuss those deriving from hydrogen-bond interactions, as well as the First Sharp Diffraction Peak (FSDP) that highlight the presence of medium range order (MRO) in the liquid. We will describe several measurements on the protic IL butylammonium nitrate and its water mixtures at different molar fractions, where both features can be found, and show how EDXD patterns can account for the modulation of these features with the composition. In the end, we will show how the change of FSDP spectral feature that occurs during the fusion of alky- lammonium chlorides can be tracked with a multiangular ADXD Rietveld diffrac- tometer.
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