Surface effects on the structure and mobility of the ionic liquid C(6)C(1)ImTFSI in silica gels
Journal article, 2014

We report on how the dynamical and structural properties of the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (C(6)C(1)ImTFSI) change upon different degrees of confinement in silica gels. The apparent diffusion coefficients of the individual ions are measured by H-1 and F-19 pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy, while the intermolecular interactions in the ionogels are elucidated by Raman spectroscopy. In addition, the local structure of the ionic liquid at the silica interface is probed by solid-state NMR spectroscopy. Importantly, we extend this study to a wider range of ionic liquid-to-silica molar ratios (x) than has been investigated previously, from very low (high degree of confinement) to very high (liquid-like gels) ionic liquid contents. Diffusion NMR measurements indicate that a solvation shell, with a significantly lower mobility than the bulk ionic liquid, forms at the silica interface. Additionally, the diffusion of the C(6)C(1)Im(+) and TFSI- ions decreases more rapidly below an observed molar ratio threshold (x < 1), with the intrinsic difference in the self-diffusion coefficient between the cation and anion becoming less pronounced. For ionic liquid molar ratio of x < 1, Raman spectroscopy reveals a different conformational equilibrium for the TFSI- anions compared to the bulk ionic liquid, with an increased population of the cisoid isomers with respect to the transoid. Concomitantly, at these high degrees of confinement the TFSI- anion experiences stronger ion-ion interactions as indicated by the evolution of the TFSI- characteristic vibrational mode at similar to 740 cm(-1). Furthermore, solid-state 2D Si-29{H-1} HETCOR NMR measurements establish the interactions of the ionic liquid species with the silica surface, where the presence of adsorbed water results in weaker interactions between Si-29 surface moieties and the hydrophobic alkyl protons of the cationic C(6)C(1)Im(+) molecules.

HYDROGEN SULFATE

JOURNAL OF CHEMICAL PHYSICS

ELECTROLYTES

1965

PULSED-FIELD GRADIENT

TRANSPORT

IONOGELS

EJSKAL EO

V42

X-RAY-SCATTERING

MESOPOROUS SILICA

CONFORMATIONAL ISOMERISM

DIFFUSION-COEFFICIENT

NMR

P288

Author

Moheb Nayeri

Chalmers, Chemical and Biological Engineering, Applied Surface Chemistry

M. T. Aronson

University of California

Diana Bernin

University of Gothenburg

B. F. Chmelka

University of California

Anna Martinelli

Chalmers, Chemical and Biological Engineering, Applied Surface Chemistry

Soft Matter

1744-683X (ISSN) 1744-6848 (eISSN)

Vol. 10 30 5618-5627

Subject Categories

Physical Chemistry

DOI

10.1039/c4sm00642a

More information

Latest update

2/28/2018