Charge transport and diffusion of ionic liquids in nanoporous silica membranes.
Charge transport in 1-hexyl-3-methylimidazolium hexafluorophosphate ionic liquid in oxidized nanoporous silicon membranes 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 coefficient is obtained in quantitative agreement with independent PFG NMR measurements. More than 10-fold systematic decrease in the effective diffusion coefficient from the bulk value is observed in hydrophilic silica nanopores. A model assuming a reduced mobility at the pore-matrix interface is shown to provide a quantitative explanation for the remarkable decrease of effective transport quantities (such as diffusion coefficient, dc conductivity and consequently, the dielectric loss) of the ionic liquid in non-silanized membranes. This approach is supported by the observation that silanization of porous silica membranes results in a significant increase of the effective diffusion coefficient, which approaches the value for the bulk liquid.
Iacob
Ciprian
C
Institute of Experimental Physics I, University of Leipzig, Linnéstr. 5, 04103, Leipzig, Germany. iacob@rz.uni-leipzig.de
Sangoro
Joshua Rume
JR
Papadopoulos
Periklis
P
Schubert
Tilman
T
Naumov
Sergej
S
Valiullin
Rustem
R
Kärger
Jörg
J
Kremer
Friedrich
F
D001881:Borates / Q000737:chemistry; D058266:Dielectric Spectroscopy; D004058:Diffusion; D007093:Imidazoles / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D058608:Nanopores / Q000648:ultrastructure*; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000737:chemistry*
C528767:1-hexyl-3-methylimidazolium; D001881:Borates; D007093:Imidazoles; D052578:Ionic Liquids; D012822:Silicon Dioxide