Dynamics in supercooled glycerol by high resolution stimulated Brillouin gain spectroscopy

Grubbs, W. Tandy; MacPhail, Richard A.

doi:10.1063/1.466503

Cited by 30 publications

(29 citation statements)

References 52 publications

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“…2A. There, the data derived from the present experiment are compared with those obtained by using lower-frequency techniques (21)(22)(23). We observe that the sound velocity measured in the present experiment does not reach the corresponding macroscopic value, not even at the lowest probed q value of ∼1 nm −1 .…”

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confidence: 75%

Breakdown of the Debye approximation for the acoustic modes with nanometric wavelengths in glasses

Monaco

Giordano²

2009

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

177

155

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On the macroscopic scale, the wavelengths of sound waves in glasses are large enough that the details of the disordered microscopic structure are usually irrelevant, and the medium can be considered as a continuum. On decreasing the wavelength this approximation must of course fail at one point. We show here that this takes place unexpectedly on the mesoscopic scale characteristic of the medium range order of glasses, where it still works well for the corresponding crystalline phases. Specifically, we find that the acoustic excitations with nanometric wavelengths show the clear signature of being strongly scattered, indicating the existence of a cross-over between well-defined acoustic modes for larger wavelengths and ill-defined ones for smaller wavelengths. This cross-over region is accompanied by a softening of the sound velocity that quantitatively accounts for the excess observed in the vibrational density of states of glasses over the Debye level at energies of a few milli-electronvolts. These findings thus highlight the acoustic contribution to the well-known universal low-temperature anomalies found in the specific heat of glasses.disordered systems | elastic properties | inelastic X-ray scattering | vibrational density of states G lasses display a set of universal low-temperature properties (1). In particular, at a temperature of ∼10 K the specific heat is characterized by an excess over the level predicted by the continuum Debye model. This excess, absent in the corresponding crystalline phases, is related to the so-called boson peak, an excess over the Debye level that appears at energies of a few milli-electronvolts in the vibrational density of states. The physical origin of this universal property has been livelily discussed in the literature for many decades; however, an agreed on solution is still lacking. For example, one interpretation supports the idea that the boson peak is produced by soft vibrations that would be present in glasses in addition to the acoustic ones (2-4). Another interpretation is mainly based on models for the vibrational dynamics of glasses in terms of harmonic oscillators with disorder in the force constants: it supports the idea that the boson peak marks the transition between acoustic-like excitations and a disorder-dominated regime for the vibrational spectrum (5-7). Qualitatively similar results appear as well in recently developed theories for the vibrational spectrum of model systems with random spatial variations in the elastic moduli (8). In another interpretation, the boson peak is related to the characteristic vibrations of nanometric clusters (9, 10) that would exist in the glass as a consequence, for example, of a spatially inhomogeneous cohesion and that would hybridize with the acoustic modes (11). The idea of an inhomogeneous elastic response has been recently reconsidered by using a different approach: numerical studies show that the classical elasticity description breaks down in glasses on the mesoscopic length scale (12)(13)(14), and the boson peak woul...

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mentioning

confidence: 75%

Breakdown of the Debye approximation for the acoustic modes with nanometric wavelengths in glasses

Monaco

Giordano²

2009

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

177

155

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“…8. In the same figure, we report two different ansatzs for the unrelaxed speed of sound obtained assuming either a linear T -dependence of M ∞ [24] or a linear T -dependence of c ∞ [28,30]. In Ref.…”

Section: B the Limiting High Frequency Sound Velocitymentioning

confidence: 99%

“…IV B. In particular, several sets of data for c 0 are available in the literature [24,28,30], obtained in different and narrow temperature ranges below 360 K and above 440 K. They are typically described by almost linear trends with different slopes. In addition, we present here new ultrasonic data measured in an intermediate temperature range between 306.5 K and 389.5 K. These data are magnified in Fig.…”

Section: Data Analysis a Acoustic Properties Of Glycerolmentioning

confidence: 99%

“…3 also shows different linear extrapolations of the unrelaxed adiabatic velocity taken from Refs. [24,28,30] circles) which will be presented in the next section. Finally, Fig.…”

Section: Data Analysis a Acoustic Properties Of Glycerolmentioning

confidence: 99%

“…Impulsive stimulated Brillouin and thermal light scattering (ISBS and ISTS) experiments [28,29] have provided information on the sound dispersion and absorption and on the structural relaxation at low temperatures and for different q values. Stimulated Brillouin gain (SBG) spectroscopy has been also used to probe the dynamics of supercooled and glassy glycerol [30]. Very recently, the density response of supercooled glycerol to an impulsive stimulated thermal grating has been studied in the 200-340 K temperature range in order to separate the structural relaxation from thermal diffusion processes [31].…”

Section: Introductionmentioning

confidence: 99%

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Density fluctuations in the intermediate glass-former glycerol: A Brillouin light scattering study

Comez

Fioretto

Scarponi

et al. 2003

The Journal of Chemical Physics

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Brillouin scattering has been used to measure the dynamic structure factor of glycerol as a function of temperature from the high temperature liquid to the glassy state. Our investigation aims at understanding the number and the nature of the relaxation processes active in this prototype glass forming system in the high frequency region. The associated character of glycerol is reflected by a rather simple relaxations pattern, while the contributions coming from intra-molecular channels are negligible in the GHz frequency region. The temperature behavior of the characteristic frequency and lifetime of the longitudinal acoustic modes is analyzed, suggesting that a phenomenological model which only includes the structural (α) process and the unrelaxed viscosity is able to catch the leading contributions to the dynamics of the density fluctuations. This ansatz is also supported by a combined analysis of light and inelastic x-ray scattering spectra. The temperature dependence of the characteristic time of the α-process, τα, obtained by a full-spectrum analysis conforms to the α-scale universality, i.e. the values τα revealed by different experimental techniques are proportional the ones to the others. The non-erogodicity parameter smoothly decreases on increasing the temperature, and no signature of the cusp-like behavior predicted by the idealized mode coupling theory and observed in other glass-formers is found in glycerol.

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Complex dynamics and the stimulated gain spectrum of pentylcyanobiphenyl in the isotropic phase

Miller¹,

MacPhail²

1995

Chemical Physics Letters

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Dynamics in supercooled glycerol by high resolution stimulated Brillouin gain spectroscopy

Cited by 30 publications

References 52 publications

Breakdown of the Debye approximation for the acoustic modes with nanometric wavelengths in glasses

Breakdown of the Debye approximation for the acoustic modes with nanometric wavelengths in glasses

Density fluctuations in the intermediate glass-former glycerol: A Brillouin light scattering study

Complex dynamics and the stimulated gain spectrum of pentylcyanobiphenyl in the isotropic phase

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