Jul 6 – 10, 2015
Institute of Nuclear Physics PAN, Kraków
Europe/Warsaw timezone

Effect of pressure on time and length scales of molecular dynamics in the density scaling regime

Jul 9, 2015, 5:50 PM
15m
Institute of Nuclear Physics PAN, Kraków

Institute of Nuclear Physics PAN, Kraków

Crown Piast Hotel

Speaker

Dr Andrzej Grzybowski (Institute of Physics, University of Silesia)

Description

Our thorough analyses of high pressure experimental data of various glass formers that belong to different material groups (such as van der Waals supercooled liquids, polymer melts, and supercooled ionic liquids) clearly show that some previous suppositions concerning interrelations between time and length scales of molecular dynamics near the glass transition require revisiting. This is a straightforward consequence of a phenomenon of isochronal decoupling observed by us [1-3] between time and dynamic length scales of molecular dynamics, which have been determined using the structural relaxation time τ and the maximum of the four-point dynamic susceptibility function χ4max. At first glance, these results seem to be disadvantageous to perspectives of finding a simple universal description of the glass transition and related phenomena. However, a very successful application of proper density scaling law to the decoupling phenomena yields a very positive outcome of our investigations. What is more, very recently, we have established [4] an analogous pattern of the density scaling behavior for the total system entropy S defined thermodynamically and the excess entropy Sex defined in the way employed in the theory of isomorphs as a difference between S and the entropy of an ideal gas at the same density and temperature. As a consequence, the phenomena of isochronal decoupling between τ, χ4max, S, and Sex explored by us using high pressure experimental data can be described by a general relation τ = hXΔxγwX(X)) with ΔXγ = γ – γX, where X = τ, χ4max, S, and Sex. The relation clearly shows that the time scale τ of molecular dynamics cannot be in general any unique function of X (= χ4max, S, and Sex). To formulate such a proper function hX in case of real glass formers, an additional density dependent factor is required. In the power law density scaling regime, the factor is a power density function, the exponent of which is a difference between the scaling exponents γ and γX and can be considered as a good measure of the isochronal decoupling between the time scale of molecular dynamics τ and the physical quantity X. [1] A. Grzybowski, K. Koperwas, K. Kolodziejczyk, K. Grzybowska, and M. Paluch, J. Phys. Chem. Lett. 4, 4273 (2013). [2] K. Koperwas, A. Grzybowski, K. Grzybowska, Z. Wojnarowska, A. P. Sokolov, and M. Paluch, Phys. Rev. Lett. 111, 125701 (2013). [3] A. Grzybowski, K. Kolodziejczyk, K. Koperwas, K. Grzybowska, and M. Paluch, Phys. Rev. B 85, 220201(R) (2012). [4] K. Grzybowska, A. Grzybowski, S. Pawlus, J. Pionteck, and M. Paluch, arXiv:1406.4563v3.

Primary author

Dr Andrzej Grzybowski (Institute of Physics, University of Silesia)

Co-authors

Mr Kajetan Koperwas (Institute of Physics, University of Silesia) Dr Katarzyna Grzybowska (Institute of Physics, University of Silesia) Prof. Marian Paluch (Institute of Physics, University of Silesia)

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