The approach of generalized collective modes is applied to the study of dispersion curves of collective excitations along isothermal lines of supercritical pure Lennard-Jones fluid. An effect of structural relaxation and other nonhydrodynamic relaxation processes on the dispersion law is discussed. A simple analytical expression for the dispersion law in the long-wavelength region of acoustic excitations is obtained within a three-variable viscoelastic model of generalized hydrodynamics. It is shown that the deviation from the linear dependence in the long-wavelength region can be either "positive" or "negative" depending on the ratio between the high-frequency (elastic) and isothermal speed of sound. An effect of thermal fluctuations on positive and negative dispersion is estimated from the analytical solution of a five-variable thermoviscoelastic model that generalizes the results of the viscoelastic treatment. Numerical results are reported for a Lennard-Jones supercritical fluid along two isothermal lines T* = 1.71, 4.78 with different densities and discussed along the theoretical expressions derived. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442412]

Collective excitations in supercritical fluids: Analytical and molecular dynamics study of "positive" and "negative" dispersion / Taras, Bryk; Ihor, Mryglod; Scopigno, Tullio; Ruocco, Giancarlo; Federico, Gorelli; Mario, Santoro. - In: THE JOURNAL OF CHEMICAL PHYSICS. - ISSN 0021-9606. - 133:2(2010), p. 024502. [10.1063/1.3442412]

Collective excitations in supercritical fluids: Analytical and molecular dynamics study of "positive" and "negative" dispersion

SCOPIGNO, TULLIO;RUOCCO, Giancarlo;
2010

Abstract

The approach of generalized collective modes is applied to the study of dispersion curves of collective excitations along isothermal lines of supercritical pure Lennard-Jones fluid. An effect of structural relaxation and other nonhydrodynamic relaxation processes on the dispersion law is discussed. A simple analytical expression for the dispersion law in the long-wavelength region of acoustic excitations is obtained within a three-variable viscoelastic model of generalized hydrodynamics. It is shown that the deviation from the linear dependence in the long-wavelength region can be either "positive" or "negative" depending on the ratio between the high-frequency (elastic) and isothermal speed of sound. An effect of thermal fluctuations on positive and negative dispersion is estimated from the analytical solution of a five-variable thermoviscoelastic model that generalizes the results of the viscoelastic treatment. Numerical results are reported for a Lennard-Jones supercritical fluid along two isothermal lines T* = 1.71, 4.78 with different densities and discussed along the theoretical expressions derived. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442412]
2010
01 Pubblicazione su rivista::01a Articolo in rivista
Collective excitations in supercritical fluids: Analytical and molecular dynamics study of "positive" and "negative" dispersion / Taras, Bryk; Ihor, Mryglod; Scopigno, Tullio; Ruocco, Giancarlo; Federico, Gorelli; Mario, Santoro. - In: THE JOURNAL OF CHEMICAL PHYSICS. - ISSN 0021-9606. - 133:2(2010), p. 024502. [10.1063/1.3442412]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/495107
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