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
Artikel i vetenskaplig tidskrift, 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

Författare

Mounesha Garaga Nagendrachar

Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi

Moheb Nayeri

Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi

Anna Martinelli

Kemi och kemiteknik, Tillämpad kemi, Teknisk ytkemi

Journal of Molecular Liquids

0167-7322 (ISSN)

Vol. 210 169-177

Ämneskategorier

Fysikalisk kemi

Kemi

DOI

10.1016/j.molliq.2015.06.055