Thermodynamic Scaling of the Dynamics of a Strongly Hydrogen-Bonded Glass-Former

Romanini, Michela; Barrio, Marı́a; Macovez, Roberto; Ruiz-Martín, M. D.; Capaccioli, S.; Tamarit, J. Ll.

doi:10.1038/s41598-017-01464-2

Cited by 47 publications

(53 citation statements)

References 53 publications

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“…We also compare our results with other procedures, such as the superposition of relaxation times (γ IPL ), the expression proposed by Casalini and Roland (γ * ), and an experimental prediction of the isomorph theory (γ isom ) mentioned in the introduction. The route to the scaling exponent proposed by Casalini and Roland, in which continuity of the entropy at the glass transition is assumed, has been shown to work effectively in several van der Waals and hydrogenbonded glass-forming liquids, as well as in polymeric materials [5,25]. From Table I, one observes that the values of γ's obtained through these three methods are in fair agreement with the average value we would obtain using Eq.…”

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confidence: 73%

“…For the latter, the state point dependence of the scaling exponent is an essential ingredient.As a special case, Alba-Simionesco, Kivelson and Tarjus (AKT) have investigated the validity of a scaling law for activated dynamics where the scaling exponent only depends on density [18][19][20], but not on temperature. Regarding γ a material constant is an even more constraining assumption, which is only valid if the potential part of the Hamiltonian can be approximated by a sum of inverse power-laws (IPL) r −n pair interactions plus an arbitrary constant (the IPL hypothesis) [3,[21][22][23][24][25]. Then the scaling exponent is independent of state-point (γ IPL = n/3) and the relaxation time falls on a master curve when plottet along ρ γ /T .…”

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Experimental Evidence for a State-Point-Dependent Density-Scaling Exponent of Liquid Dynamics

et al. 2019

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A large class of liquids have hidden scale invariance characterized by a scaling exponent. In this letter we present experimental evidence that the scaling exponent of liquid dynamics is statepoint dependent for the glass-forming silicone oil tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl ether (5PPE). From dynamic and thermodynamic properties at equilibrium, we use a method to estimate the value of γ at any state point of the pressure-temperature plane, both in the supercooled and normal liquid regimes. We find agreement between the average exponents and the value obtained by superposition of relaxation times over a large range of state-points. We confirm the state-point dependence of γ by reanalyzing data of 20 metallic liquids and two model liquids.Decreasing the temperature (T ) or increasing the density (ρ) by applying pressure of liquids lead to slowing down of the molecular dynamics and eventually a glass transition if crystallization is avoided [1,2]. It has been demonstrated that for numerous low molecular weight liquids and polymers, the relaxation time or other dynamic quantities can be superimposed onto a master curve within the experimental uncertainty when plotted as a function of ρ γ /T . The scaling exponent γ is thus sometimes referred to as a material constant [3][4][5]. In this letter, we show that γ is in fact state-point dependent and can be measured at a single state point. In the following we will use subscripts to distinguish definitions of γ's.Let τ be the structural relaxation time measured from the loss-peak frequency of the electric permittivity. We will express τ in reduced units of m/k B T ρ 2/3 where m is a atomic/molecular/polymer-segment mass and define the scaling exponent of τ as [6]In this general definition the exponent depends on the state point and the fixed quantity (τ in the above case). A physical interpretation of γ τ is that it quantifies the relative contribution of volume and thermal energy to the temperature evolution of the molecular mobility [7]. Similar to the structural relaxation time, configurational adiabats can also be associated with a scaling exponent:In general, two scaling exponents of different observables (structural, dynamical or thermodynamic) will have different values. However, if the system has so-called "hidden scale-invariance" [6, 8] then all scaling exponents of different properties will have the same value. In Ref.[9] * asanz@ruc.dk † urp@ruc.dk it was experimentally shown that γ τ = γ Sex at one state point of the silicone oil DC704. This result is spectacular since hidden scale-invariance can only be present in a class of systems [10,11]. This class is believed to include systems where van der Waals (vdW) interactions dominate, but exclude systems where hydrogen-bondes (HB) dominates the Hamiltonian [12]. The isomorph theory [6,8,10,12] is a framework for describing systems where the potential energy function U (R) possesses hidden scale invariance (here, R is the collective coordinate of the system). Formally hidden scale inva...

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Experimental Evidence for a State-Point-Dependent Density-Scaling Exponent of Liquid Dynamics

et al. 2019

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“…This equation has been verified for a large number of materials by many different experimental groups. [20,21,22,23,24,25,26] Although the AA equation was originally introduced empirically, It has been also derived from theoretical models. [27,28] The dependence of the density from pressure and temperature is well described by the Tait equation of state (EoS) [29].…”

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confidence: 99%

On the pressure dependence of the thermodynamical scaling exponent γ

Casalini

Ransom

2020

Soft Matter

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Since its initial discovery more than fifteen years ago, the thermodynamical scaling of the dynamics of supercooled liquids has been used to provide many new important insights in the physics of liquids, particularly on the link between dynamics and intermolecular potential. A question that has long been discussed is whether the scaling exponent  is a constant or it depends on pressure. Here we offer a simple method to determine the pressure dependence of  using only the pressure dependence of the glass transition and the equation of state.Using this new method we find that for the six non-associated liquids investigated  always decreases with increasing pressure. Importantly in all cases the value of  remains always larger than 4. Liquids having  closer to 4 at low pressure show a smaller change in  with pressure. We argue that this result has very important consequences for the experimental determination of the functional form of the repulsive part of the potential in liquids.

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“…While most metals and van der Waals bonded liquids are believed to have isomorphs in the condensed-phase part of their phase diagram, systems with significant directional bonding like covalently or hydrogen-bonded systems are not expected to have isomorphs. 32,37,38 The Lennard-Jones (LJ) liquid belongs to the former class of the so-called Roskilde (R)-simple systems, 31,[39][40][41][42][43] which includes most systems with more or less spherical interaction symmetry, the property that traditionally defines a "simple" system. 8 We use below the isomorph theoretical framework as a guide to arrive at an expression for how simple liquids' viscosity varies throughout the high-density part of the thermodynamic phase diagram.…”

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