### Abstract

thermoviscoelastic frequency-dependent response functions, there are generally three independent functions. For stochastic dynamics we show that there are only two independent response functions; for this case it is shown how analytic continuation may be utilized to express the third response functions in terms of two others. Operational criteria are presented for the linear thermoviscoelasticity being described by a single "order" parameter, in which case there is just one independent thermoviscoelastic response function. It is shown that a description with a single "order" parameter applies to a good approximation whenever thermal equilibrium fluctuations of fundamental variables like energy and pressure are strongly correlated. Results from computer simulations showing that this is the case for a number of simple glass-forming liquids, as well as a few exceptions, are briefly presented. Finally, we briefly discuss a new conjecture according to which experiments at varying temperature and pressure follow the density scaling expression for the relaxation time, τ = F(ρ^x/T ) (ρ and T are density and temperature), if and only if the liquid is "strongly correlating", i.e., to a good approximation is described by a single "order" parameter.

Original language | English |
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Journal | Journal of Physics: Condensed Matter |

Volume | 20 |

Issue number | 24 |

Number of pages | 8 |

ISSN | 0953-8984 |

DOIs | |

Publication status | Published - 2008 |

### Cite this

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**Glass-forming liquids: one or more "order" parameters".** / Bailey, Nicholas; Christensen, Tage Emil; Jakobsen, Bo; Niss, Kristine; Olsen, Niels Boye; Pedersen, Ulf Rørbæk; Schrøder, Thomas; Dyre, J. C.

Research output: Contribution to journal › Journal article › Research › peer-review

TY - JOUR

T1 - Glass-forming liquids: one or more "order" parameters"

AU - Bailey, Nicholas

AU - Christensen, Tage Emil

AU - Jakobsen, Bo

AU - Niss, Kristine

AU - Olsen, Niels Boye

AU - Pedersen, Ulf Rørbæk

AU - Schrøder, Thomas

AU - Dyre, J. C.

N1 - Paper id:: 244113

PY - 2008

Y1 - 2008

N2 - We first summarize the classical arguments that the vast majority of glass-forming liquids require more than one ‘order' parameter for their description. Critiques against this conventional wisdom are then presented, and it is argued that the matter deserves to be reconsidered in the light of recent experimental developments. Out of the eight basicthermoviscoelastic frequency-dependent response functions, there are generally three independent functions. For stochastic dynamics we show that there are only two independent response functions; for this case it is shown how analytic continuation may be utilized to express the third response functions in terms of two others. Operational criteria are presented for the linear thermoviscoelasticity being described by a single "order" parameter, in which case there is just one independent thermoviscoelastic response function. It is shown that a description with a single "order" parameter applies to a good approximation whenever thermal equilibrium fluctuations of fundamental variables like energy and pressure are strongly correlated. Results from computer simulations showing that this is the case for a number of simple glass-forming liquids, as well as a few exceptions, are briefly presented. Finally, we briefly discuss a new conjecture according to which experiments at varying temperature and pressure follow the density scaling expression for the relaxation time, τ = F(ρ^x/T ) (ρ and T are density and temperature), if and only if the liquid is "strongly correlating", i.e., to a good approximation is described by a single "order" parameter.

AB - We first summarize the classical arguments that the vast majority of glass-forming liquids require more than one ‘order' parameter for their description. Critiques against this conventional wisdom are then presented, and it is argued that the matter deserves to be reconsidered in the light of recent experimental developments. Out of the eight basicthermoviscoelastic frequency-dependent response functions, there are generally three independent functions. For stochastic dynamics we show that there are only two independent response functions; for this case it is shown how analytic continuation may be utilized to express the third response functions in terms of two others. Operational criteria are presented for the linear thermoviscoelasticity being described by a single "order" parameter, in which case there is just one independent thermoviscoelastic response function. It is shown that a description with a single "order" parameter applies to a good approximation whenever thermal equilibrium fluctuations of fundamental variables like energy and pressure are strongly correlated. Results from computer simulations showing that this is the case for a number of simple glass-forming liquids, as well as a few exceptions, are briefly presented. Finally, we briefly discuss a new conjecture according to which experiments at varying temperature and pressure follow the density scaling expression for the relaxation time, τ = F(ρ^x/T ) (ρ and T are density and temperature), if and only if the liquid is "strongly correlating", i.e., to a good approximation is described by a single "order" parameter.

U2 - 10.1088/0953-8984/20/24/244113

DO - 10.1088/0953-8984/20/24/244113

M3 - Journal article

VL - 20

JO - Journal of Physics: Condensed Matter

JF - Journal of Physics: Condensed Matter

SN - 0953-8984

IS - 24

ER -