Rotational and Translational Diffusion of Ionic Liquids in Silica Nanopores

  • Ciprian Iacob
  • Joshua Sangoro
  • Wycliffe Kipnusu
  • Friedrich Kremer
Part of the Advances in Dielectrics book series (ADVDIELECT)


Diffusion in ionic liquids (ILs) contained in silica nanopores is investigated in a wide frequency and temperature range by a combination of Broadband Dielectric Spectroscopy (BDS) and Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). By applying the Einstein-Smoluchowski relations to the dielectric spectra, diffusion coefficients are obtained in quantitative agreement with independent PFG NMR. More than tenfold systematic decrease in the effective diffusion coefficient (for [HMIM] [PF\(_{6}\)]) from the bulk value is observed in the silica nanopores. A model assuming a reduced mobility at the IL/porous matrix is proposed and shown to provide quantitative explanation for the remarkable decrease of effective transport quantities (such as diffusion coefficient, DC conductivity and consequently, the dielectric loss) of the IL in bare porous silica membranes. This approach is supported by the observation that silanization of silica nanopores results in significant increase of the effective diffusion coefficient, which approaches the value for the bulk liquid. For a different IL ([BMIM] [BF\(_{4}\)]), it is observed that ionic mobility at lower temperatures is enhanced by more than two decades under nanoconfinement in comparison to the bulk value. This increase in the diffusivity is attributed to reduced packing density of the ions in the nanopores. In summary, the resultant macroscopic transport properties of glass-forming ILs in confining space are determined by a subtle interplay between surface- and confinement-effects.


Ionic liquids Diffusion Confinement and surface effects Broadband dielectric spectroscopy Silica nanopores Ionic mobility 



Broadband Dielectric Spectroscopy

BMIM BF\(_{4}\)

1-Butyl-3-methylimidazolium tetrafluoroborate


Fourier Transform Infrared



HMIM PF\(_{6}\)

1-hexyl-3-methylimidazolium hexafluorophosphate


Nuclear Magnetic Resonance


Pulsed Field Gradient Nuclear Magnetic Resonance


Scanning and Tunneling Electron Microscopy





We thank Dr. Sergej Naumov for help in conducting the PFG-NMR measurements and Dr. Periklis Papadopoulos for FT-IR measurements. Financial support from DFG (Germany), NOW (The Netherlands) within IRTG “Diffusion in Porous Materials” and DFG Priority Program SPP 1191 on Ionic Liquids is gratefully acknowledged. J. R. S. thanks the University of Tennessee-Knoxville for financial support through tenure-track faculty research start-up funds. Ciprian Iacob thanks the Penn State University and St. Jude Medical for financial support.


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Ciprian Iacob
    • 1
  • Joshua Sangoro
    • 2
  • Wycliffe Kipnusu
    • 3
  • Friedrich Kremer
    • 3
  1. 1.Department of Materials Science and EngineeringPenn State UniversityState CollegeUSA
  2. 2.Department of Chemical and Biomolecular EngineeringUniversity of TennesseeKnoxvilleUSA
  3. 3.Institute of Experimental Physics IUniversity of LeipzigLeipzigGermany

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