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Issue 20, 2018
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X-Ray diffraction and resonance shear measurement of nano-confined ionic liquids

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Abstract

X-ray diffraction measurement at the SPring-8 synchrotron was employed to investigate the structures of two types of imidazolium-based ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][NTF2]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]), confined between silica surfaces by varying the surface separation distances of ca. 500 nm (bulk liquid), ca. 10 nm, and ca. 2 nm (hard wall thickness). The obtained diffraction profiles and intensities were discussed by considering the structures and properties of the nano-confined ILs between the silica surfaces investigated by resonance shear measurement (RSM) and molecular dynamics simulation (MD) in our previous reports. [C4mim][NTf2] showed two diffraction peaks at q = 8.8 nm−1 (spacing d = 0.71 nm) and at q = 14.0 nm−1 (spacing d = 0.45 nm) at the greatest distance (D = ca. 500 nm), which were assigned to the interval between the same ions (anion–anion or cation–cation) within the polar network of [C4mim][NTf2] and the interval between the neighboring anion–cation, respectively. The positions of these two peaks remained the same at D = ca. 10 nm and at the hard wall (D = ca. 2 nm) and their intensity factor increased, indicating that both the cation and anion existed in the same layer. This result was consistent with the checkerboard structure of [C4mim][NTf2] on the silica surface computer simulated in our previous studies. On the other hand, [C4mim][BF4] showed a peak at q = 15.4 nm−1 (spacing d = 0.41 nm) corresponding to the anion–cation interval at the greatest distance (D = ca. 500 nm). This peak became broader and weaker at D = ca. 12 nm and at D = ca. 2 nm.

Graphical abstract: X-Ray diffraction and resonance shear measurement of nano-confined ionic liquids

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Article information


Submitted
24 Dec 2017
Accepted
23 Feb 2018
First published
08 Mar 2018

Phys. Chem. Chem. Phys., 2018,20, 13714-13721
Article type
Paper

X-Ray diffraction and resonance shear measurement of nano-confined ionic liquids

K. Tomita, M. Mizukami, S. Nakano, N. Ohta, N. Yagi and K. Kurihara, Phys. Chem. Chem. Phys., 2018, 20, 13714
DOI: 10.1039/C7CP08611C

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