Effect of the alkyl chain length in 1-alkyl-3-methylimidazolium ionic liquids on inter-molecular interactions and rotational dynamics: A combined vibrational and NMR spectroscopic study
Journal article, 2015
We have investigated the effect of increasing the alkyl chain length, n, in 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C
n
C
1
ImTFSI) ionic liquids on both inter-molecular interactions and rotational dynamics. This has been addressed by combining 1D 1H and T
1
relaxation NMR spectroscopy with vibrational spectroscopy, including both Raman and infrared. We find that the vibrational modes sensitive to inter-molecular interactions change only slightly with an increased alkyl chain length, with negligible changes for chains longer than the hexyl (n > 6). This is nicely corroborated by 1H chemical shift changes, in particular of the aromatic protons. The 13C correlation times, τ
c
, of the individual carbon atoms reveal that while the overall rotational mobility decreases with n, different dynamical properties are observed with the polar domains becoming the most dynamic and the imidazolium ring and its closest chain segment the most rigid. We conclude that the formation of segregated nano-domains in C
n
C
1
ImTFSI is accompanied by the formation of nano-dynamical heterogeneities, which can explain why classical theories fail to describe the dependence on n of macroscopically observed properties.
Liquids
Spectroscopic studies
Dynamics
Spectroscopic analysis
Rotational mobility
Inter-molecular interactions
Dynamical properties
Dynamical heterogeneities
Bis(trifluoromethane sulfonyl)imide
Molecular interactions
Local dynamics
NMR spectroscopy
Intermolecular interactions
Alkyl chain lengths
Nuclear magnetic resonance spectroscopy
Chain length
Carbon
Chemical shift
Vibrational spectroscopy
Molecular structure
Ionic liquids
Author
Mounesha Garaga Nagendrachar
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Moheb Nayeri
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Anna Martinelli
Chalmers, Chemistry and Chemical Engineering, Applied Chemistry
Journal of Molecular Liquids
0167-7322 (ISSN)
Vol. 210 169-177Subject Categories
Physical Chemistry
Chemical Sciences
DOI
10.1016/j.molliq.2015.06.055