Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition

Fujara, F.; Geil, Burkhard; Sillescu, H.; Fleischer, G.

doi:10.1007/bf01323572

Cited by 546 publications

(567 citation statements)

References 66 publications

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“…However, it is well-known that near T g , translations are often enhanced relative to reorientational motions (such as associated with the dielectric α-process) 82,83,84 . The result is that a double logarithmic plot of σ versus τ α will have a slope deviating from unity 85 .…”

Section: Resultsmentioning

confidence: 99%

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Casalini

Roland

2005

Macromolecules

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Dielectric spectroscopy measurements over a broad range of temperature and pressure were carried out on poly(oxybutylene) (POB), a type-A polymer (dielectrically-active normal mode). There are three dynamic processes appearing at lower frequency, the normal and segmental relaxation modes, and a conductivity arising from ionic impurities. In combination with pressure-volume-temperature measurements, the dielectric data were used to assess the respective roles of thermal energy and density in controlling the relaxation times and their variation with T and P. We find that the local segmental and the global relaxation times are both a single function of the product of the temperature times the specific volume, with the latter raised to the power of 2.65. The fact that this scaling exponent is the same for both modes indicates they are governed by the same local friction coefficient, an idea common to most models of polymer dynamics. Nevertheless, near T g , their temperature dependences diverge. The magnitude of the scaling exponent reflects the relatively weak effect of density on the relaxation times. This is usual for polymers, as the intramolecular bonding, and thus interactions between directly bonded segments, are only weakly sensitive to pressure. This insensitivity also means that the chain end-to-end distance is invariant to P, conferring a near pressure-independence of the (density-normalized) normal mode dielectric strength.The ionic conductivity dominates the low frequency portion of the spectra. At lower temperatures and higher pressures, this conductivity becomes decoupled from the relaxation modes (different T-dependence), and exhibits a significantly weaker density effect. At frequencies higher than the structural relaxation, both an excess wing on the flank of the α-peak and a secondary relaxation are observed. From their relative sensitivities to pressure, we ascribe the former to an unresolved Johari-Goldstein (JG) relaxation, while the higher frequency peak is unrelated to the glass transition. These designations are consistent with the relaxation time calculated for the JG process. 2The dynamic properties of the POB are essentially the same as those of polypropylene glycol, in accord with their similar chemical structures. However, POB is less fragile (weaker T gnormalized temperature dependence), its relaxation times less sensitive to density changes, and facilitating the measurements herein, its normal mode has a substantially larger dielectric strength

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Section: Resultsmentioning

confidence: 99%

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Casalini

Roland

2005

Macromolecules

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“…SE relation is obeyed at sufficiently high temperature but violated around 1.3T g , where T g is the glass transition temperature, thus indicating decoupling between translational diffusion and viscosity. In contrast, it was observed for ortho-terphenyl (23,24,26) that rotational diffusion and viscosity remain strongly coupled (i.e., obey the SED relation) even very close to T g . A corollary is that translational and rotational diffusion decouple from each other at low temperature.…”

mentioning

confidence: 84%

“…However, they might break down at low temperature. Pioneering experiments were performed by the groups of Sillescu (23)(24)(25) and Ediger (26)(27)(28) where a series of molecular glassformers were investigated. SE relation is obeyed at sufficiently high temperature but violated around 1.3T g , where T g is the glass transition temperature, thus indicating decoupling between translational diffusion and viscosity.…”

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confidence: 99%

Viscosity of deeply supercooled water and its coupling to molecular diffusion

Dehaoui

Issenmann

Caupin

2015

Proc. Natl. Acad. Sci. U.S.A.

204

213

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The viscosity of a liquid measures its resistance to flow, with consequences for hydraulic machinery, locomotion of microorganisms, and flow of blood in vessels and sap in trees. Viscosity increases dramatically upon cooling, until dynamical arrest when a glassy state is reached. Water is a notoriously poor glassformer, and the supercooled liquid crystallizes easily, making the measurement of its viscosity a challenging task. Here we report viscosity of water supercooled close to the limit of homogeneous crystallization. Our values contradict earlier data. A single power law reproduces the 50-fold variation of viscosity up to the boiling point. Our results allow us to test the Stokes-Einstein and Stokes-Einstein-Debye relations that link viscosity, a macroscopic property, to the molecular translational and rotational diffusion, respectively. In molecular glassformers or liquid metals, the violation of the Stokes-Einstein relation signals the onset of spatially heterogeneous dynamics and collective motions. Although the viscosity of water strongly decouples from translational motion, a scaling with rotational motion remains, similar to canonical glassformers.supercooled water | viscosity | Stokes-Einstein relations W ater, considered as a potential glassformer, has been a longlasting topic of intense activity. Its possible liquid-glass transition was reported 50 years ago to be in the vicinity of 140 K (1, 2). However, ice nucleation hinders the access to this transition from the liquid side. Bypassing crystallization requires hyperquenching the liquid at tremendous cooling rates, ca. 10 7 K · s −1 (3). As a consequence, many questions about supercooled and glassy water and its glass-liquid transition remain open (4-7).As an example, crystallization of water is accompanied by one of the largest known relative changes in sound velocity, which has been attributed to the relaxation effects of the hydrogen bond network (8, 9). Indeed, whereas the sound velocity is around 1,400 m · s −1 in liquid water at 273 K, it reaches around 3,300 m · s −1 in ice at 273 K and a similar value in the known amorphous phases of ice at 80 K (10). Such a large jump is usually the signature of a strong glass, i.e., one in which relaxation times or viscosity follow an Arrhenius law upon cooling. However, pioneering measurements on bulk supercooled water by NMR (11) and quasi-elastic neutron scattering (12), as well as recent ones by optical Kerr effect (8, 9), reveal a large super-Arrhenius behavior between 340 and 240 K, similar to what is observed in fragile glassformers (13,14). The temperature dependence of the relaxation time is well described by a power law (8, 9), as expected from mode-coupling theory (15, 16), which usually applies well to liquids with a small change of sound velocity upon vitrification. Based on these and other observations, it has been hypothesized that supercooled water experiences a fragile-tostrong transition (17). This idea has motivated experimental efforts to measure dynamic properties of supercooled wate...

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“…10 In spite of such discrepancies, which are of the same order as ours, the consensus is that above T C , probes that are well-coupled to the solvent follow the SED law. 12 As noted in other work, 13 the relation ͗ ͘ϰ merely shows that solvent structure, and hydrogen bonding in the case of associated liquids, affects the rotational correlation time and the viscosity. A breakdown in the proportionality, e.g., a breakdown in the SED, offers clues about the nature of the approach to the glass transition.…”

Section: ͓S0021-9606͑98͒51946-0͔mentioning

confidence: 99%

Response to “Comment on ‘A 250 GHz ESR study of o-terphenyl dynamic cage effects above TC’ ” [J. Chem. Phys. 109, 10523 (1998)]

Earle

Mościcki

Polimeno

et al. 1998

The Journal of Chemical Physics

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We address the points raised by Giordano and Leporini (GL) and show that accounting properly for the nonexponential decay of the rotational correlation function leads to improved agreement with the Stokes–Einstein–Debye (SED) relation above the crossover temperature TC for those probes 3,3′-dimethyloxazolidinyl-N-oxy-2′,3-5α-cholestane (CSL), and perdeuterated 2,2′,6,6′-tetramethyl-4-methyl aminopiperidinyl-N-oxide) (MOTA) that are well-coupled to the viscous modes of o-terphenyl (OTP) when the average relaxation rate 16〈τ〉 is plotted versus 1/T. On the other hand, 2,2′,6,6′-tetramethyl-4-piperidine-N-oxide (PDT) shows simple Arrhenius behavior in this regime, because of weak coupling to the solvent cage, inconsistent with SED, which was clearly shown in our paper. We also suggest that the difference in chemical structure of the PDT probe, studied by us, compared to 2,2′,6,6′-tetramethylpiperidine-N-oxyl (TEMPO), studied by GL, accounts for the difference in the low-temperature relaxation behavior of the two probes.

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Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition

Cited by 546 publications

References 66 publications

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Temperature and Density Effects on the Local Segmental and Global Chain Dynamics of Poly(oxybutylene)

Viscosity of deeply supercooled water and its coupling to molecular diffusion

Response to “Comment on ‘A 250 GHz ESR study of o-terphenyl dynamic cage effects above TC’ ” [J. Chem. Phys. 109, 10523 (1998)]

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