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Issue 28, 2017
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In search of invariants for viscous liquids in the density scaling regime: investigations of dynamic and thermodynamic moduli

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Abstract

In this paper, we report the nontrivial results of our investigations of dynamic and thermodynamic moduli in search of invariants for viscous liquids in the density scaling regime by using selected supercooled van der Waals liquids as representative materials. Previously, the dynamic modulus MpT (defined in the pressure–temperature representation by the ratio of isobaric activation energy and activation volume) as well as the ratio BT/Mp–T (where BT is the thermodynamic modulus defined as the inverse isothermal compressibility) have been suggested as some kinds of material constants. We have established that they are not valid in the explored wide range of temperatures T over a dozen decades of structural relaxation times τ. The temperature dependences of Mp–T and BT/Mp–T have been elucidated by comparison with the well-known measure of the relative contribution of temperature and density fluctuations to molecular dynamics near the glass transition, i.e., the ratio of isochoric and isobaric activation energies. Then, we have implemented an idea to transform the definition of the dynamic modulus Mp–T from the pT representation to the VT one. This idea relied on the disentanglement of combined temperature and density fluctuations involved in isobaric parameters and has resulted in finding an invariant for viscous liquids in the density scaling regime, which is the ratio of thermodynamic and dynamic moduli, BT/MV–T. In this way, we have constituted a characteristic of thermodynamics and molecular dynamics, which remains unchanged in the supercooled liquid state for a given material, the molecular dynamics of which obeys the power density scaling law.

Graphical abstract: In search of invariants for viscous liquids in the density scaling regime: investigations of dynamic and thermodynamic moduli

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Publication details

The article was received on 20 Feb 2017, accepted on 26 Jun 2017 and first published on 26 Jun 2017


Article type: Paper
DOI: 10.1039/C7CP01144J
Citation: Phys. Chem. Chem. Phys., 2017,19, 18348-18355
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    In search of invariants for viscous liquids in the density scaling regime: investigations of dynamic and thermodynamic moduli

    A. Jedrzejowska, A. Grzybowski and M. Paluch, Phys. Chem. Chem. Phys., 2017, 19, 18348
    DOI: 10.1039/C7CP01144J

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