TY - JOUR
T1 - Understanding the Liquid Structure in Mixtures of Ionic Liquids with Semiperfluoroalkyl or Alkyl Chains
AU - Elstone, Naomi S.
AU - Shimizu, Karina
AU - Shaw, Emily V.
AU - Lane, Paul D.
AU - D'Andrea, Lucía
AU - Demé, Bruno
AU - Mahmoudi, Najet
AU - Rogers, Sarah E.
AU - Youngs, Sarah
AU - Costen, Matthew L.
AU - McKendrick, Kenneth G.
AU - Canongia Lopes, Jose N.
AU - Bruce, Duncan W.
AU - Slattery, John M.
N1 - Funding Information:
The authors thank the EPSRC (N.S.E. and P.D.L.) for support (EP/T031174/1) and the ILL and ISIS for beamtime (9-10-1720 and RB2220026). K.S. and J.N.C.L. thank Fundação para a Ciência e Tecnologia, FCT/MCTES (Portugal) for the financial support through the CEEC contract (IST-ID/100/2018 to K.S.) and through projects UIDB/00100/2020 and LA/P/0056/2020. a
Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society
PY - 2023/8/24
Y1 - 2023/8/24
N2 - By mixing ionic liquids (ILs), it is possible to fine-tune their bulk and interfacial structure. This alters their physical properties and solvation behavior and is a simple way to prepare a collection of ILs whose properties can be tuned to optimize a specific application. In this study, mixtures of perfluorinated and alkylated ILs have been prepared, and links between composition, properties, and nanostructure have been investigated. These different classes of ILs vary substantially in the flexibility and polarizability of their chains. Thus, a range of useful structural and physical property variations are accessible through mixing that will expand the library of IL mixtures available in an area that to this point has received relatively little attention. In the experiments presented herein, the physical properties and bulk structure of mixtures of 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM][Tf2N] and 1-(1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM-F13][Tf2N] have been prepared. The bulk liquid structure was investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS, respectively) experiments in combination with atomistic molecular dynamics simulations and the measurement of density and viscosity. We observed that the addition of [C8MIM-F13][Tf2N] to [C8MIM][Tf2N] causes changes in the nanostructure of the IL mixtures that are dependent on composition so that variation in the characteristic short-range correlations is observed as a function of composition. Thus, while the length scales associated with the apolar regions (polar non-polar peak─PNPP) increase with the proportion of [C8MIM-F13][Tf2N] in the mixtures, perhaps surprisingly given the greater volume of the fluorocarbon chains, the length scale of the charge-ordering peak decreases. Interestingly, consideration of the contact peak shows that its origins are both in the direct anion···cation contact length scale and the nature (and hence volume) of the chains appended to the imidazolium cation.
AB - By mixing ionic liquids (ILs), it is possible to fine-tune their bulk and interfacial structure. This alters their physical properties and solvation behavior and is a simple way to prepare a collection of ILs whose properties can be tuned to optimize a specific application. In this study, mixtures of perfluorinated and alkylated ILs have been prepared, and links between composition, properties, and nanostructure have been investigated. These different classes of ILs vary substantially in the flexibility and polarizability of their chains. Thus, a range of useful structural and physical property variations are accessible through mixing that will expand the library of IL mixtures available in an area that to this point has received relatively little attention. In the experiments presented herein, the physical properties and bulk structure of mixtures of 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM][Tf2N] and 1-(1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C8MIM-F13][Tf2N] have been prepared. The bulk liquid structure was investigated using a combination of small-angle X-ray and neutron scattering (SAXS and SANS, respectively) experiments in combination with atomistic molecular dynamics simulations and the measurement of density and viscosity. We observed that the addition of [C8MIM-F13][Tf2N] to [C8MIM][Tf2N] causes changes in the nanostructure of the IL mixtures that are dependent on composition so that variation in the characteristic short-range correlations is observed as a function of composition. Thus, while the length scales associated with the apolar regions (polar non-polar peak─PNPP) increase with the proportion of [C8MIM-F13][Tf2N] in the mixtures, perhaps surprisingly given the greater volume of the fluorocarbon chains, the length scale of the charge-ordering peak decreases. Interestingly, consideration of the contact peak shows that its origins are both in the direct anion···cation contact length scale and the nature (and hence volume) of the chains appended to the imidazolium cation.
UR - http://www.scopus.com/inward/record.url?scp=85168461618&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcb.3c02647
DO - 10.1021/acs.jpcb.3c02647
M3 - Article
C2 - 37555779
SN - 1520-6106
VL - 127
SP - 7394
EP - 7407
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 33
ER -