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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.

Charge transport and structural dynamics in a homologous pair of ammonium and phosphonium based room temperature ionic liquids (ILs) have been characterized over a wide temperature range using broadband dielectric spectroscopy and quasi-elastic light scattering spectroscopy. We have found that the ionic conductivity of the phosphonium based IL is significantly enhanced relative to the ammonium homolog, and this increase is primarily a result of a lower glass transition temperature and higher ion mobility. Additionally, these ILs exhibit pronounced secondary relaxations which are strongly influenced by the atomic identity of the cation charge center. While the secondary relaxation in the phosphonium IL has the expected Arrhenius temperature dependence characteristic of local beta relaxations, the corresponding relaxation process in the ammonium IL was found to exhibit a mildly non-Arrhenius temperature dependence in the measured temperature range--indicative of molecular cooperativity. These differences in both local and long-range molecular dynamics are a direct reflection of the subtly different inter-ionic interactions and mesoscale structures found in these homologous ILs. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. [ABSTRACT FROM AUTHOR]

Glassy dynamics and charge transport are studied for the polymeric ionic liquid (PIL) poly[tris(2-(2-methoxyethoxy)ethyl)ammonium acryloxypropyl sulfonate] (PAAPS) with varying molecular weight (9700, 44200, 51600, and 99500 g/mol) by broadband dielectric spectroscopy (BDS) in a wide frequency (10-2-107 Hz) and temperature range (100-400 K) and by DSC- and AC-chip calorimetry. The dielectric spectra are characterized by a superposition of (i) relaxation processes, (ii) charge transport, and (iii) electrode polarization. The relaxation processes (i) are assigned to the dynamic glass transition and a secondary relaxation. Charge transport (ii) can be described by the random free-energy barrier model as worked out by Dyre et al.; the Barton-Namikawa-Nakajima (BNN) relationship is well fulfilled over more than 8 decades. Electrode polarization (iii) follows the characteristics as analyzed by Serghei et al., with deviations on the low frequency side. The proportionality between the relaxation rate of the dynamic glass transition and the charge carrier hopping rate reflects the nature of charge transport as glass transition assisted hopping. Hereby, the PIL under study exposes the highest dc-conductivity values observed for this class of materials below 100 °C, so far; and for the first time a conductivity increase by rising degree of polymerization. The comparison of the polymeric ionic liquids under study with others implies conclusions on the design of novel highly conductive PILs. [ABSTRACT FROM AUTHOR]

A homologous series of 16 polymeric ionic liquids (PIL) are investigated based on monovalent and bivalent telechelic polyisobutylene (PIB) carrying the ionic liquid (IL)-like cationic headgroup (N,N,N-triethylammonium or 1-methylpyrrolidinium) and Br, NTf2, OTf, or pTOS as anions. Molecular dynamics, charge transport, and polarization at mesoscopic scales are analyzed over a wide frequency (10-2-107 Hz) and temperature (200-400 K) range by means of broadband dielectric spectroscopy (BDS); additionally, differential scanning calorimetry (DSC) is employed. In detail, (i) three molecular relaxation processes are observed including the dynamic glass transition of the polymeric matrix, (ii) a conductivity relaxation originating from charge transport in the IL-like moieties, and (iii) a weak electrode polarization caused by the accumulation of mobile charge carriers at the metal interfaces. The net conductivity of the PIL as a whole is quantitatively described by an effective-medium approximation (EMA) reflecting the microphase-separated character of the PIL under study. [ABSTRACT FROM AUTHOR]

Inorder to understand the nature of the exceedingly low ionic conductivityof aprotic ammonium ionic liquids (ILs), we have measured the chargetransport and structural dynamics of methyltrioctylammonium bis(trifluoromethylsulfonyl)imide[m3oa][ntf2] over a broad temperature range using broadband dielectricspectroscopy, depolarized dynamic light scattering (DDLS), rheology,and pulsed field gradient nuclear magnetic resonance. We demonstratethat the low level of ionic conductivity in this material is due tothe combined effects of reduced ion mobility as well as reduced freeion concentration relative to other types of ILs. Furthermore, detailedanalysis of the DDLS spectra reveals a slow process in addition tothe structural α relaxation that we attribute to reorientationalmotion of alkyl aggregates. These findings indicate that hydrophobicaggregation strongly influences the charge transport mechanism ofaprotic ammonium ionic liquids with long aliphatic side chains. [ABSTRACT FROM AUTHOR]