Fast secondary dynamics for enhanced charge transport in polymerized ionic liquids.

Segmental dynamics is considered as a major factor governing ionic conductivity of polymerized ionic liquids (PILs), envisioned as potential electrolytes in fuel cells and batteries. Our dielectric studies performed in T-P thermodynamic space on ionene, composed of the positively charged polymer backbone and freely moving anions, indicate that other relaxation modes, completely ignored so far, can affect the charge transport in PILs as well. We found that fast mobility manifested by a secondary ß process promotes segmental dynamics and thereby increases ionic conductivity making the studied material a first coupled PIL of superionic properties. The molecular mechanism underlying such a ß process has been identified as Johari-Goldstein relaxation giving experimental proof that fast secondary relaxations of intermolecular origin exist also in PILs and thereby reveal a universal character.

Structurally Related Scaling Behavior in Ionic Systems.

We examine the density scaling properties of two ionic materials, a classic aprotic low molecular weight ionic liquid, 1-butyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide ([BMIm][BETI]), and a polymeric ionic liquid, poly(3-methyl-1,2,3-triazolium bis(trifluoromethylsulfonyl)imide) (TPIL). Density scaling is known to apply rigorously to simple liquids lacking specific intermolecular associations such as hydrogen bonds. Previous work has found that ionic liquids conform to density scaling over limited ranges of temperature and pressure. In this work, we find that the dc-conductivity of [BMIm][BETI] accurately scales for density changes of 17%; however, there is a departure from scaling for TPIL for even more modest variations of temperature and pressure. The entropy of both ionic samples conforms to density scaling only if the scaling exponent is allowed to vary linearly with the magnitude of the entropy.

Exchange Process in the Dielectric Loss of Molecular and Macromolecular Ionic Conductors in the Interfacial Layers Formed by Electrode Polarization Effects.

Here we report a first analytical approach to determine the spectral dependence of the complex permittivity function of molecular and macromolecular ionic conductors in the interfacial layers formed by electrode polarization effects. We show that a previous model of electrode polarization effects that was successfully applied for describing the dielectric behavior of ionic liquids ( Serghei, A.; Tress, M.; Sangoro, J. R.; Kremer, F. Electrode polarization and charge transport at solid interfaces. Phys. Rev. B 2009 , 80 , 184301 ) can be now generalized and applied for polymer/ionic liquid blends as well as for poly(ionic liquid)s. The determined dielectric function of the interfacial layers reveals a dramatic change in the charge transport process manifested by a large decrease in conductivity. Our approach brings the first evidence for a relaxation peak detected in the dielectric loss of the interfaces, which is attributed to an exchange process between the interface and the bulk. This study gives new insights into the mechanism of charge transport at interfaces and could thus contribute to a better correlation between the dielectric properties of ion conducting materials and their electrochemical behavior at interfaces.

A 1,2,3-triazolate lithium salt with ionic liquid properties at room temperature.

A triethylene glycol-based 1,2,3-triazolate lithium salt with ionic liquid properties at room temperature is synthesized in three steps including copper-catalysed cycloaddition between alkyne-functionalized monomethoxy-triethylene glycol and azidomethyl pivalate, followed by the deprotection of the methyl pivalate group and further lithiation of the 1H-1,2,3-triazole intermediate. The resulting lithium 1,2,3-triazolate is characterized by NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, broadband dielectric spectroscopy, electrochemical impedance spectroscopy and cyclic voltamperometry. This approach provides new opportunities for the further development of highly functional molecular and macromolecular lithium salts.

Poly(vinyl ester 1,2,3-triazolium)s: a new member of the poly(ionic liquid)s family.

A vinyl ester monomer carrying a pendant 1,2,3-triazole group is synthesized in two steps and polymerized by cobalt-mediated radical polymerization. Subsequent alkylation with N-methyl bis[(trifluoromethyl)sulfonyl]imide affords the corresponding poly(vinyl ester 1,2,3-triazolium). This unprecedented example of poly(vinyl ester ionic liquid) exhibits an ionic conductivity of 9.2 × 10(-7) S cm(-1) at 30 °C.