Does fragility depend on pressure? A dynamic light scattering study of a fragile glass-former

Paluch, Marian; Gapiński, Jacek; Patkowski, A.; Fischer, Erhard W.

doi:10.1063/1.1362293

Cited by 81 publications

(91 citation statements)

References 48 publications

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“…Decoupling between DR and DLS experiments has sometimes been reported [10]. It does not seem to be the case here.…”

Section: I-introductionmentioning

confidence: 63%

“…References are a) [18], b) [14], c) [17], d) [41], e) [26], f) [42], g) [12], h) [13], i) [40], j) [8,9,10], k) [44], l) [5]. Table 2 Parameters n, b and ρ o appearing in [42], d) [12], e) [43], f) [8], g) [5,39].…”

Section: Are Computed From V(tp)mentioning

confidence: 99%

“…The Angell plot [2], which represents the logarithm of relaxation times τ (or viscosity η) as a function of For the time being, there is no theoretical answer to these questions but recent experimental data can be analyzed along these lines. Indeed, new experimental developments have allowed to perform viscosity [5,6] as well as light-scattering [7][8][9][10][11][12][13][14][15] and dielectric measurements [16][17][18][19] at variable temperature and pressure. Thus, the exploration of a large portion of the phase diagram and the measurement of the corresponding quantities is now possible.…”

Section: I-introductionmentioning

confidence: 99%

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Scaling the $\alpha $ -relaxation time of supercooled fragile organic liquids

et al. 2004

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:It was shown recently [1] that the structural α-relaxation time τ of supercooled o-terphenyl depends on a single control parameter Γ, which is the product of a function of density E(ρ), by the inverse temperature T -1 . We extend this finding to other fragile glassforming liquids using light-scattering data. Available experimental results do not allow to discriminate between several analytical forms of the function E(ρ), the scaling arising from the separation of density and temperature in Γ. We also propose a simple form for τ(Γ), which depends only on three material-dependent parameters, reproducing relaxation times over 12 orders of magnitude. I-IntroductionThe steady increase over more than 12 orders of magnitude of the shear viscosity η, or of the structural α-relaxation time τ measured by dielectric or light-scattering spectroscopic methods, is among the spectacular features that accompany the liquid-glass transition [2]. The latter can take place in a large variety of liquids ranging from mineral oxides, salts, organic polymers, metallic alloys, to simple molecular liquids. Under cooling, these liquids avoid crystallisation at the melting temperature T m and become a glass at a lower temperature T g .For low molecular weight glassforming materials, a glass is usually defined as a liquid whose relaxation times τ are larger than 10 2 seconds, a phenomenon that takes place at some temperature T g . In spite of its frequent occurrence and of continuous theoretical and experimental efforts over the last fifty years, this transition remains one of the least understood phenomena in condensed matter physics. In particular, one still does not fully grasp how and on which parameters, usually called control parameters, these relaxation times τ depend [3,4]. Obviously, in simple glassforming colloids the only control parameter is the density. Conversely, would the structural relaxation of a liquid at equilibrium be only due to jumps over energy barriers that are independent from temperature and density, τ might have a simple Arrhenius behaviour and the only control parameter would be temperature. The Angell plot [2], which represents the logarithm of relaxation times τ (or viscosity η) as a function of orders of magnitude, they showed that the data can be scaled using control parameters of the same form as in OTP, n becoming material dependent. Previously, a scaling was shown to hold in glycerol by . Also ref. [24] showed that the domain of density explored in the experiments was too small to ascertain the analytical form of E(ρ Table 1. At each pressure and temperature, the corresponding density can be obtained from the Tait interpolation formula, whose form and parameters are also collected in Table 1. Table 2 as well as that obtained from unpublished PCS data on BMPC (1,1-bis(p-methoxyphenyl)cyclohexane ) [25]. We add also the n value obtained by the scaling of the dielectric α-relaxation time in KDE (cresolphtaleine-dimethyl ether) [26].The values of n vary from 3.8 to 7.5.We note that similar result...

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“…Decoupling between DR and DLS experiments has sometimes been reported [10]. It does not seem to be the case here.…”

Section: I-introductionmentioning

confidence: 63%

Section: Are Computed From V(tp)mentioning

confidence: 99%

Section: I-introductionmentioning

confidence: 99%

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Scaling the $\alpha $ -relaxation time of supercooled fragile organic liquids

et al. 2004

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“…This is shown more clearly in Fig.10, where m P is plotted versus P. In light of our finding that the isobaric fragility always decreases with pressure, we reconsider 1,2-polybutadiene (PB) [36], the sole case of an m P (determined using eq. (4)) reportedly increasing with P. The τ measured for PB for four isotherms at varying P are displayed in Fig.11 [36], along with the best fit (solid line) of the data to the empirical function [37] 0 0…”

Section: -Isobaric and Isochoric Fragilitymentioning

confidence: 99%

Scaling of the supercooled dynamics and its relation to the pressure dependences of the dynamic crossover and the fragility of glass formers

2005

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Master curves of the relaxation time, τ, or viscosity, η, versus T -1 V -γ , where T is temperature, V the specific volume, and γ a material constant, are used to deduce the effect of pressure on the dynamic crossover and the fragility. The crossover is determined from the change in slope of derivative plots of the relaxation times or viscosities. We confirm our previous findings that the value of τ or η at the crossover is independent of both T and P; that is, the dynamic crossover is associated with a characteristic value of the relaxation time. Previous determinations were limited to liquids having crossovers occurring at large values of τ ( > 10 -6 s), whereas by interpolating within T -1 V -γ space, we extend the analysis to smaller values of the crossover time. Using the superpositioned data, the dynamic crossover can be observed in isochoric data, where it is found that the relaxation time at the crossover for constant volume is equivalent to the value obtained under (the more usual) condition of constant pressure.Similarly, from the scaling analysis, isobaric relaxation times at high pressure are deduced from experimental measurements at atmospheric pressure. We find for all glass-formers studied, that the fragility (normalized temperature dependence of τ or η) is a decreasing function of pressure. This conclusion is less subject to uncertainties in the measurements than published determinations of the pressure coefficient of fragility. Finally, we show that an empirical function, having the form of the Cohen-Grest relation but without connection to any free volume model, parameterizes the master curves, and accurately describes the data over all measured conditions. 2

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“…Similarly, Paluch et al [19] have defined a pressurefragility index as (6) Although this definition is dimensionless like the temperature version, it is undefined for cases where p g → 0. An earlier definition by Paluch et al [20] does not scale the pressure by p g and will be more useful for a μ g = 10 10 Pa s.…”

Section: (B)mentioning

confidence: 99%

Fragility and the dynamic crossover in lubricants

Bair

Roland

Casalini³

2007

Proceedings of the Institution of Mechanical Engineers, Part J:

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Abstract:The property of fragility in glass forming liquids is introduced to elastohydrodynamic lubrication (EHL). Using viscosity measurements for three liquids that have been the subject of traction studies the fragility of liquids is shown to be important to EHL traction and the property that most influences the representative (Eyring) stress. The derivative Stickel analysis is then carried out for lubricants. Using viscosity measurements, the dynamic crossover is detected for the first time in lubricants. The viscosity at the crossover is either constant or varies slowly with temperature and pressure and the crossover pressure varies with temperature in a manner similar to the glass transition pressure. The free-volume model fails to predict the occurrence of the dynamic crossover.

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Does fragility depend on pressure? A dynamic light scattering study of a fragile glass-former

Cited by 81 publications

References 48 publications

Scaling the $\alpha $ -relaxation time of supercooled fragile organic liquids

Scaling the $\alpha $ -relaxation time of supercooled fragile organic liquids

Scaling of the supercooled dynamics and its relation to the pressure dependences of the dynamic crossover and the fragility of glass formers

Fragility and the dynamic crossover in lubricants

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