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Title: Heterogeneous Nature of Relaxation Dynamics of Room-Temperature Ionic Liquids (EMIm)2[Co(NCS)4] and (BMIm)2[Co(NCS)4]

Dynamic crossover above Tg has been recognized as a characteristic feature of molecular dynamics of liquids approaching glass transition. Experimentally, it is manifested as a change in Vogel–Fulcher–Tammann dependence or a breakdown of the Stokes–Einstein and related relations. In this study, we report the exception from this rather general pattern of behavior. By means of dielectric, ultrasonic, rheological, and calorimetric methods, dynamics of two good ionic conductors (BMIm)2[Co(NCS)4] and (EMIm)2[Co(NCS)4] of less common stoichiometry (2:1) was studied in a very broad temperature range. However, none of the mentioned dynamic changes was observed in the entire studied temperature range. On the contrary, the single VFT and the same fractional Walden coefficient were found for conductivity and viscosity changes over 12 decades. Finally and moreover, ultrasonic studies revealed that the data at temperatures which cover the normal liquid region cannot be fitted by a single exponential decay, and the Cole–Cole function should be used instead.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [4] ;  [5] ;  [6] ;  [2]
  1. Univ. of Silesia, Katowice (Poland). Inst. of Chemistry
  2. Univ. of Silesia, Katowice (Poland). Inst. of Physics; Univ. of Silesia, Chorzow (Poland). Silesian Center for Education and Interdisciplinary Research (SMCEBI)
  3. Leibniz Inst. for Catalysis, Rostock (Germany)
  4. Univ. of Silesia, Katowice (Poland). Inst. of Physics
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences
  6. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry
Publication Date:
OSTI Identifier:
1324141
Grant/Contract Number:
DEC-2011/03/B/ST3/02072; CHE-1213444
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 119; Journal Issue: 35; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Silesia, Katowice (Poland)
Sponsoring Org:
USDOE; National Science Centre (Poland); National Science Foundation (NSF) (United States)
Contributing Orgs:
Leibniz Inst. for Catalysis, Rostock (Germany)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE