Marian PALUCH1, Wojnarowska ZANETA1
1University of Silesia, Institute of Physics, KATOWICE, Poland
Recently, a fascinating idea called the thermodynamic or density scaling was proposed to jointly describe the dependence of molecular dynamics of glass-forming liquids on thermal and packing effects [1, 2]. According to this idea, both isobaric and isothermal data can be expressed as a single universal curve if they are plotted against the new variable TVγ, where T and V denote temperature and specific volume, respectively, and γ is the scaling exponent. This presentation focuses on analyzing the electrical conductivity of several ionic liquids (ILs) measured at different temperatures and pressures in terms of the density scaling concept . Our results clearly show that for all studied ILs, the scaling exponent is a state-point independent parameter that can be related to the exponent in the inverse power law describing the repulsive part of the effective short-range potential for intermolecular interactions . It will also be shown how the idea of density scaling can be applied to analyze entropy data. However, in this case, the scaling exponent is no more a state-point independent parameter and is equivalent to Grüneisen parameter. Interestingly, for all tested samples, a linear relationship between Grüneisen parameter (scaling exponent) and entropy was obtained, and more importantly, the generated slope shows a close relation to the typical interactions (van der Waals and Coulomb forces, and H-bonds). Therefore, we establish a new correlation for this group of compounds.
 G. Floudas, M. Paluch, A. Grzybowski, and K. L. Ngai, Molecular Dynamics of Glass-Forming Systems: Effects of
Pressure: Advances in Dielectrics, Springer-Verlag, Berlin 2011
 A. Grzybowski, M. Paluch, The Scaling of Relaxation Processes: Universality of Density Scaling Ch, vol. 4, Springer, Berlin, 2018.
 M. Paluch, Dielectric properties of ionic liquids, Springer 2016
 Z. Wojnarowska, M. Musia?, M. Dzida and M. Paluch, Phys. Rev. Lett. 123, 125702 (2019)