Speaker
Dr
Miroslaw Galazka
(Institute of Nuclear Physics Polish Academy of Sciences)
Description
`Spectrum of a dielectric permittivity for supercooled disordered phases most often is composed of two relaxation processes [1]: a main relaxation process (called $\alpha$ process) followed by resolved, unresolved (also called ‘excess wing phenomena’), or both secondary processes ($\beta$ processes). Although there are many models describing dielectric relaxation [2-6] none of them describes the relaxation processes in supercooled disordered phases with a good precision, because of some simplifications introduced. Debye model [2] describes relaxation for non-interacting electric dipoles or electric dipoles in diluted non-polar medium whereas Debye-like models, i.e. Cole-Cole [3], Cole-Davidson [4], Havriliak-Negami [5], describe relaxation for non-interacting electric dipoles in viscous medium. Therefore, some scaling equations of the dielectric response were proposed [7-9] to describe molecular dynamics as a function of frequency of measuring field for various temperatures. However, they are limited to scaling of the imaginary part of dielectric permittivity only [7-9], and Nagel and co-authors model [7-8] refers in fact to systems with ‘special’ values of long-range and short-range correlation parameters of molecular interactions. Therefore, we have proposed a general form of scaling equation [10-11] that can be applied to the imaginary part of permittivity $\epsilon$”($f$) as well as to the real part of permittivity $\epsilon$’($f$)-$\epsilon_\infty$. The proposed scaling of the dielectric response applied to supercooled disordered phases, i.e. supercooled isotropic liquid phase and supercooled plastic-crystal phase, shows that behavior of resolved and/or unresolved $\beta$ relaxations strictly depends on the parameters of the main relaxation process. One can conclude that the main relaxation process and the secondary ones are not independent processes.`
References
[1] A. Kudlik et al., `$\textit{J. Non-Cryst. Solids}$` `$\textbf{235-237}$` (1998) 406.
[2] F. Kremer, A. Söchnhals, `$\textit{Broadband Dielectric Spectroscopy}$`, Springer-Verlag Berlin Heidelberg (2003).
[3] K. S. Cole, R. H. Cole, `$\textbf{J. Chem. Phys.}$` `$\textbf{9}$` (1941) 341.
[4] D. W. Davidson, R. H. Cole, `$\textit{J. Chem. Phys.}$` `$\textbf{18}$` (1951) 1417.
[5] S. Havriliak, C. A. Negami, `$\textit{J. Polym. Sci. Part C}$` `$\textbf{14}$` (1966) 99.
[6] L. A. Dissado, R. M. Hill, `$\textit{Proc. R. Soc. A}$` `$\textbf{390}$` (1983) 131.
[7] N. Menon, S. R. Nagel, `$\textit{Phys. Rev. Lett.}$` `$\textbf{71}$` (1993) 4095.
[8] P. K. Dixon, L. Wu, S. R. Nagel, B. D. Williams, J. P. Carini, `$\textit{Phys. Rev. Lett.}$` `$\textbf{65}$` (1990) 1108.
[9] Z. Dendzik, M. Paluch, Z. Gburski, J. Zioło, `$\textit{J. Phys.: Condens. Matt.}$` `$\textbf{9}$` (1997) L339.
[10] M. Gałązka, E. Juszyńska-Gałązka, N. Osiecka, M. Massalska-Arodź, A. Bąk, `$\textit{J. Appl. Phys.}$` `$\textbf{118}$` (2015) 064101.
[11] M. Gałązka, E. Juszyńska-Gałązka, N. Osiecka, A. Bąk, `$\textit{Phase Transitions}$` `$\textbf{89}$` (2016) 341.
`Acknowledgments`
`Partial support by the 2014-2016 PAS-CNR bilateral project “Studies of phase polymorphism and dynamics in selected soft materials” and by the 2017-2019 PAS-CNR bilateral project “Multidisciplinary studies of structural and dynamic properties of glass-forming compounds” is acknowledged.`
Primary author
Dr
Miroslaw Galazka
(Institute of Nuclear Physics Polish Academy of Sciences)
