Heterogeneous Nature of Relaxation Dynamics of Room-Temperature Ionic Liquids (EMIm)2[Co(NCS)4] and (BMIm)2[Co(NCS)4]
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- 作者：Stella Hensel-Bielowka ; Zaneta Wojnarowska ; Marzena Dzida ; Edward Zor臋bski ; Micha艂 Zor臋bski ; Monika Geppert-Rybczy艅ska ; Tim Peppel ; Katarzyna Grzybowska ; Yangyang Wang ; Alexei P. Sokolov ; Marian Paluch
- 刊名：Journal of Physical Chemistry C
- 出版年：2015
- 出版时间：September 3, 2015
- 年：2015
- 卷：119
- 期：35
- 页码：20363-20368
- 全文大小：392K
- ISSN：1932-7455
文摘
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鈥揊ulcher鈥揟ammann dependence or a breakdown of the Stokes鈥揈instein and related relations. In this paper, 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. 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鈥揅ole function should be used instead.