Unusual features of long-range density fluctuations in glass-forming organic liquids: A Rayleigh and Rayleigh-Brillouin light scattering study

Patkowski, A.; Fischer, Erhard W.; Steffen, Werner; Gläser, H.; Baumann, Manuel; Ruths, T.; Meier, G. E. A.

doi:10.1103/physreve.63.061503

Cited by 50 publications

(43 citation statements)

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“…Some of the features may be specific of glycerol as a hydrogen-bonded, strong glass former. Other features such as the coexistence of liquid and solid domains seem present in many molecular glass formers (19) and even in dense colloidal suspensions (31). All of these questions can certainly serve as starting points for further illuminating studies of glass formation at nanometer scales.…”

Section: Discussionmentioning

confidence: 98%

“…While all techniques [NMR (7,8,11), dielectric hole-burning (13,16), light scattering (19), x-ray scattering (18), and fluorescence (6)] agree on the presence of dynamical heterogeneity, no such consensus exists about environmental exchanges. For example, exchange times are on the order of the alpha-relaxation times according to NMR (7) and dielectric relaxation (16) measurements, whereas optical techniques rather point to very slow exchange and relaxation processes (6,9,10,15,(18)(19)(20)(21). To clarify this apparent contradiction, we note that the properties of a heterogeneous ensemble of molecules in a glass-forming liquid will be spread along many dimensions.…”

Section: Discussionmentioning

confidence: 99%

“…The typical mechanisms, length scales, and time scales of environmental exchanges remain largely unclear. NMR and dielectric relaxation point to times comparable to the molecular rotation times (16,22), whereas light scattering and fluorescence show inhomogeneities with exceedingly slow relaxation (9,12,(19)(20)(21).Single-molecule fluorescence is a well established method for studying rotational diffusion (23-26). Linear dichroism, which characterizes the ratio of fluorescence intensities emitted by a single molecule on two orthogonal polarizations, is followed in real time.…”

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confidence: 99%

“…Indeed, spatially inhomogeneous dynamics (5) have been observed with a variety of techniques in many glass formers, including simple liquids (6-10) and polymers (11)(12)(13)(14)(15). Inhomogeneities have been found in the particular case of supercooled glycerol by dielectric hole burning (16), NMR (17), x-ray (18), light scattering (19), and stimulated Brillouin gain spectroscopy experiments (20,21). These observations have to be reconciled with the common view of a supercooled liquid, which is supposed to remain a normal ergodic liquid until the glass transition.…”

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confidence: 99%

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Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules

Zondervan

Kulzer

Berkhout

et al. 2007

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

147

180

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We probe the rotational diffusion of a perylene dye in supercooled glycerol, 5-25 K above the glass-transition temperature (T g ‫؍‬ 190 K) at the ensemble and the single-molecule level. The singlemolecule results point to a broad distribution of local viscosities that vary by a factor of five or more for different individual fluorophores at a given temperature. By following the same single molecules at various temperatures, we find that the distribution of local viscosities itself broadens upon approaching T g. This spatial heterogeneity is found to relax extremely slowly, persisting over hours or even days. These results convey a picture of heterogeneous liquid pockets separated by solid-like walls, which exist already well above the viscosimetric glass transition.fluorescence ͉ glass transition ͉ anisotropy ͉ correlation G lycerol is an archetypal molecular glass former. Although glycerol crystals can be grown from solution, the pure liquid readily supercools because of its high viscosity [10 3 times that of water at room temperature (1)], which is caused by the formation of a highly branched network of intermolecular hydrogen bonds. The viscosity of supercooled glycerol increases by 10 orders of magnitude between 291.8 K, the melting temperature of crystalline glycerol, and its viscosimetric glass-transition temperature T g ϭ 190 K. Throughout this range of temperatures, macroscopic rheology measurements seem consistent with the expected behavior of a Newtonian liquid, although they also reveal highly nonexponential kinetics (1-3).The necessity for cooperative motion at larger and larger scales on approaching the glass transition was recognized a long time ago by Adam and Gibbs (4). In their view, glass formation arises from dynamical arrest of cooperative domains, and their spread in sizes leads to an overall nonexponential relaxation. Indeed, spatially inhomogeneous dynamics (5) have been observed with a variety of techniques in many glass formers, including simple liquids (6-10) and polymers (11-15). Inhomogeneities have been found in the particular case of supercooled glycerol by dielectric hole burning (16), NMR (17), x-ray (18), light scattering (19), and stimulated Brillouin gain spectroscopy experiments (20, 21). These observations have to be reconciled with the common view of a supercooled liquid, which is supposed to remain a normal ergodic liquid until the glass transition. Heterogeneous regions with different relaxation dynamics are therefore expected to exchange with one another to restore ergodicity, by processes called environmental exchanges (6,9,10,12,(14)(15)(16). The typical mechanisms, length scales, and time scales of environmental exchanges remain largely unclear. NMR and dielectric relaxation point to times comparable to the molecular rotation times (16,22), whereas light scattering and fluorescence show inhomogeneities with exceedingly slow relaxation (9,12,(19)(20)(21).Single-molecule fluorescence is a well established method for studying rotational diffusion (23-26). Linear dichroism...

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules

Zondervan

Kulzer

Berkhout

et al. 2007

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

147

180

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“…The most mysterious is the phenomenon of long-range correlations (LRC) of the density fluctuations (Fischer cluster) discovered and investigated during the last decade [2][3][4][5][6][7][8][9]. In a wide temperature range above the glass transition temperature T g , the correlation length of density fluctuations is much larger than the molecule size.…”

Section: Introductionmentioning

confidence: 99%

On correlated heterogeneities of glass-forming liquids

Bakaı̆

2002

Low Temperature Physics

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The thermodynamics and structure of glass-forming liquids are considered within the framework of the heterophase fluctuation (HPF) model. The main goal of the theory developed is to fined for a description of the long-range correlations (LRC) of the density fluctuations known as the Fischer cluster. The van der Waals approximation of the HPF model shows that the liquid can have an isolated solid-fluid critical point analogous to the critical point of a gas-liquid system. Heterophase fluctuations in the form of solidlike noncrystalline and fluidlike clusters can have LRC in a narrow vicinity of the critical point. An analysis shows that the properties of the conventional critical fluctuations differ from those of the Fisher cluster. This forces one to look for another explanation of the observed LRC in glass-forming liquids. Large configurational entropy of liquids and glasses is a manifestation of multiplicity of the short-range ordering of molecules in the amorphous solidlike and fluidlike clusters. The multiplicity of short-range order results in structural heterogeneities. Random-field Ginzburg-Landau equations for the HPFs are deduced taking into account the structural heterogeneities. The random field is generated by these heterogeneities. It is found that at least three characteristic correlation scales are inherent to the HPF: the radius of local order, r 0 , which is comparable with the radius of the first coordination sphere; the random-field-controlled radius of critical fluctuations, R c ; the average correlation length of fractal aggregations formed by the correlated domains (the domains have size~R c ), x av . The length x av is the characteristic size of the Fischer cluster. The conditions for the appearance of the listed correlations are deduced by requiring that they provide minimization of the free energy of the system. The annealing kinetics and dynamics (the ultraslow modes) of the Fischer cluster are described.

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A two-fluid model for the formation of clusters close to a continuous or almost continuous transition

Pleiner

Brand

2021

Rheol Acta

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Experiments have shown that spatial heterogeneities can arise when the glass transition in polymers as well as in a number of low molecular weight compounds is approached by lowering the temperature. This formation of “clusters” has been detected predominantly by small angle light scattering and ultrasmall angle x-ray scattering from the central peak on length scales up to about 200 nm and by mechanical measurements including, in particular, piezorheometry for length scales up to several microns. Here we use a macroscopic two-fluid model to study the formation of clusters observed by the various experimental techniques. As additional macroscopic variables, when compared to simple fluids, we use a transient strain field to incorporate transient positional order, along with the velocity difference and a relaxing concentration field for the two subsystems. We show that an external homogeneous shear, as it is applied in piezorheometry, can lead to the onset of spatial pattern formation. To address the issue of additional spectral weight under the central peak we investigate the coupling to all macroscopic variables. We find that there are additional static as well as dissipative contributions from both, transient positional order, as well as from concentration variations due to cluster formation, and additional reversible couplings from the velocity difference. We also briefly discuss the influence of transient orientational order. Finally, we point out that our description is more general, and could be applied above continuous or almost continuous transitions

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Unusual features of long-range density fluctuations in glass-forming organic liquids: A Rayleigh and Rayleigh-Brillouin light scattering study

Cited by 50 publications

References 51 publications

Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules

Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules

On correlated heterogeneities of glass-forming liquids

A two-fluid model for the formation of clusters close to a continuous or almost continuous transition

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Unusual features of long-range density fluctuations in glass-forming organic liquids: A Rayleigh and Rayleigh-Brillouin light scattering study

Cited by 50 publications

References 51 publications

Local viscosity of supercooled glycerol near T g probed by rotational diffusion of ensembles and single dye molecules

Local viscosity of supercooled glycerol near T g probed by rotational diffusion of ensembles and single dye molecules

On correlated heterogeneities of glass-forming liquids

A two-fluid model for the formation of clusters close to a continuous or almost continuous transition

Contact Info

Product

Resources

About

Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules

Local viscosity of supercooled glycerol near T _g probed by rotational diffusion of ensembles and single dye molecules