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Title: Ion transport and structural dynamics in homologous ammonium and phosphonium-based room temperature ionic liquids

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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [2] ;  [6] ;  [6]
  1. Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)
  2. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States)
  3. Department of Materials Science, National Institute of Technology, Wakayama College, 77 Noshima, Nada-cho, Gobo, Wakayama 644-0023 (Japan)
  4. Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)
  5. Institute of Experimental Physics I, University of Leipzig, Linnestr. 5, 04103 Leipzig (Germany)
  6. (United States)
Publication Date:
OSTI Identifier:
22416186
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMMONIUM COMPOUNDS; CATIONS; CHARGE TRANSPORT; DIELECTRIC MATERIALS; GLASS; IONIC CONDUCTIVITY; LIGHT SCATTERING; MOBILITY; MOLECULAR DYNAMICS METHOD; MOLTEN SALTS; ORGANIC PHOSPHORUS COMPOUNDS; REFLECTION; RELAXATION; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; TRANSITION TEMPERATURE