Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Roland, C. M.; Hensel-Bielówka, S.; Paluch, Marian; Casalini, R.

doi:10.1088/0034-4885/68/6/r03

Cited by 681 publications

(1,060 citation statements)

References 445 publications

(602 reference statements)

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“…[8][9][10][11][12][13][14][15][16][17][18] Thus it has been shown that strongly correlating viscous liquids to a good approximation have all eight frequency-dependent thermoviscoelastic response functions [19][20][21] given in terms of just one 22 (i.e., are single-parameter liquids in the sense of having dynamic Prigogine-Defay ratio 19 close to unity 2,20,22 ). Strongly correlating viscous liquids moreover obey density scaling [23][24][25][26][27] to a good approximation, i.e., their dimensionless relaxation timeτ ≡ τρ 1/3 √ k B T /m (where m is the average particle mass) depends on density ρ = N /V and temperature as τ = F(ρ γ /T ). [28][29][30] Paper I 1 presented computer simulations of 13 different systems, showing that van der Waals type liquids are strongly correlating, whereas hydrogen-bonding liquids like methanol or water are not.…”

Section: Introductionmentioning

confidence: 99%

Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems

Schrøder

Gnan

Pedersen

et al. 2011

The Journal of Chemical Physics

115

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This series of papers is devoted to identifying and explaining the properties of strongly correlating liquids, i.e., liquids with more than 90% correlation between their virial W and potential energy U fluctuations in the N V T ensemble. Paper IV [N. Gnan et al., J. Chem. Phys. 131, 234504 (2009)] showed that strongly correlating liquids have "isomorphs," which are curves in the phase diagram along which structure, dynamics, and some thermodynamic properties are invariant in reduced units. In the present paper, using the fact that reduced-unit radial distribution functions are isomorph invariant, we derive an expression for the shapes of isomorphs in the WU phase diagram of generalized Lennard-Jones systems of one or more types of particles. The isomorph shape depends only on the Lennard-Jones exponents; thus all isomorphs of standard Lennard-Jones systems (with exponents 12 and 6) can be scaled onto a single curve. Two applications are given. One tests the prediction that the solid-liquid coexistence curve follows an isomorph by comparing to recent simulations by Ahmed and Sadus [J. Chem. Phys. 131, 174504 (2009)]. Excellent agreement is found on the liquid side of the coexistence curve, whereas the agreement is less convincing on the solid side. A second application is the derivation of an approximate equation of state for generalized Lennard-Jones systems by combining the isomorph theory with the Rosenfeld-Tarazona expression for the temperature dependence of the potential energy on isochores. It is shown that the new equation of state agrees well with simulations.

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Section: Introductionmentioning

confidence: 99%

Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems

Schrøder

Gnan

Pedersen

et al. 2011

The Journal of Chemical Physics

115

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“…28 However, this correlation is known to be only approximate, with various exceptions having been reported. 29,30 There is no a priori reason why the location of the dielectric loss peak, τ, should be correlated with its width, . Hence, the observed common relationship between and τ in many glassforming liquids, as shown in Figure 1, is unexpected and striking.…”

Section: Experimental Results For the Relationship Between And τmentioning

confidence: 99%

Relationship between the Nonexponentiality of Relaxation and Relaxation Time in the Problem of Glass Transition

2008

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By analyzing the experimental data for various glass-forming liquids and polymers, we find that the nonexponentiality, , and the relaxation time, τ, are commonly related: log(τ) is an approximately linear function of 1/ , followed in most cases by a crossover to a higher linear slope. We rationalize this relationship in the recently developed elastic approach to the glass transition. The key to the observed common relationship between and τ is that the two quantities are governed by the same parameter, the liquid elasticity length, d el . The increase of d el on lowering temperature increases τ and decreases , resulting in the observed common relationship between and τ. In this picture, we also discuss the crossovers of and τ at low temperature.

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“…This differs from the scaling behavior of isotropic liquids, for which plots of log τ versus T -1 V -γ are nonlinear. 18 The Arrhenius nature of the scaled data for LC implies that V γ reflects the volume-dependence of the height of the activation barrier. The two material constants, Γ and γ, would be equal if τ | were constant along the transition line T c (P).…”

Section: Introductionmentioning

confidence: 99%

Interaction Potential in Nematogenic 6CHBT

et al. 2008

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Pressure-volume-temperature (PVT) measurements were carried out on the nematic liquid crystal 4(trans-4′-n-hexylcyclohexyl)isothiocyanatobenzene (6CHBT). In combination with previous dielectric relaxation measurements at elevated pressure and new measurements extending to GHz frequencies, the characteristics of the anisotropic interaction potential were determined. The thermodynamic potential parameter, Γ, which measures the variation of the interaction energy with volume, equals 5.03 ( 0.06, with a barrier height equal to ∼7 kJ/mol. Thus, there is a low potential barrier to reorientations of the 6CHBT molecule about its short axis; however, the retarding potential is strongly volume-dependent. The longitudinal reorientational times determined for various thermodynamic conditions superpose using a scaling exponent equal to Γ within the experimental error. It then follows, as found recently for other liquid crystals, that this relaxation time must be constant along the pressure-dependent clearing line. Thus, the control parameter (e.g., Gibbs free energy) governing the competition between the anisotropic energy and the entropy must also govern the rotational dynamics in the ordered phase of this liquid crystal.

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Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Cited by 681 publications

References 445 publications

Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems

Pressure-energy correlations in liquids. V. Isomorphs in generalized Lennard-Jones systems

Relationship between the Nonexponentiality of Relaxation and Relaxation Time in the Problem of Glass Transition

Interaction Potential in Nematogenic 6CHBT

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