Inelastic X-Ray Scattering as a Probe of the Transition Between the Hydrodynamic and the Single Particle Regimes in Simple Fluids

Cunsolo, Alessandro

doi:10.5772/66126

Cited by 8 publications

(58 citation statements)

References 36 publications

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“…The hypotheses behind the DML, duly described in [1] and to which the reader is referred to for an in-depth study, are actually two, and both have an experimental background. The first is that experiments performed with the IXS and INS techniques [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] have made it possible to highlight that the mesoscopic structure of liquids is characterized by the presence of solid-like, pseudocrystalline structures, whose size being of a few molecular diameters and mass of few molecules, within which the elastic waves propagate as in the corresponding solid phase. The number and size of these structures varies with the temperature and pressure of the liquid.…”

Section: Further Discussion and Conclusionmentioning

confidence: 99%

“…The entire liquid oscillates, compressing and expanding under the effect of pressure waves, which travel at the speed of sound. When one investigates the behaviour of a liquid at very high frequencies, and therefore at small wavelengths, it is discovered that it has a mesoscopic structure similar to that of a solid, the one identified here in a picturesque and imaginative way with the icebergs, elsewhere simply called pseudo-crystalline structures (see for instance [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]).…”

Section: Introductionmentioning

confidence: 99%

“…more than double that known at traditional frequencies, 1500 m/s, and very close to that of solid water, 4000 m/s. Starting from the results of experiments performed on various liquids with INS and IXS techniques, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], the evidence that pseudo-crystalline structures "exist and persist" in liquids has gradually consolidated, their size and number depending on the liquid temperature (and pressure). These structures can obviously be discovered only when high frequency measurements are carried out, typical of INS and IXS techniques, the wavelengths of the radiation involved being small enough to reveal their presence.…”

Section: Introductionmentioning

confidence: 99%

“…. As for the temperature dependence of m , the basis for the reasoning is the experimental evidence of the presence in liquids of transversal modes [18][19][20][21][22][23][24][25][26][27][28][29][30] actives for the propagation of elastic energy by means of shear waves working as in the solid phase. These modes however persist in the liquid phase as long as solid-like structures survive.…”

Section: Introductionmentioning

confidence: 99%

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Isochoric specific heat in the Dual Model of Liquids and comparison with the Phonon theory of Liquid Thermodynamics

Peluso

2021

Preprint

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We continue in this paper to illustrate the implications of the Dual Model of Liquids (DML) by deriving the expression for the isochoric specific heat as a function of the collective degrees of freedom available at a given temperature and comparing it with the analogous expression obtained in the Phonon Theory of Liquid Thermodynamics. The Dual Model of Liquids has been recently proposed as a model describing the dynamics of liquids at the mesoscopic level. Bringing together the early pictures of Brillouin and Frenkel and the recent experimental outcomes obtained by means of high energy scattering, liquids are considered in the DML as constituted by a population of wave packets, responsible for the propagation of elastic and thermal perturbations, and of dynamic aggregates of molecules, in continuous re-arrangement, diving in an ocean of amorphous, disordered liquid. The collective degrees of freedom contribute to the exchange of energy and momentum between the material particles and the lattice particles, which the liquids are supposed to be composed of in the DML.First, we show that the expression obtained for the specific heat in the DML is in line with the experimental results. Second, its comparison with that of the Phonon Theory of Liquid Thermodynamics allows getting interesting insights about the limiting values of the collective degrees of freedom and on that of the isobaric thermal expansion coefficient, two quantities that appear related to each other in this framework

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Section: Further Discussion and Conclusionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Isochoric specific heat in the Dual Model of Liquids and comparison with the Phonon theory of Liquid Thermodynamics

Peluso

2021

Preprint

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“…This result, already foreseen in [69], was correlated with the arrangement typical of liquid water at mesoscopic scale, marking a transition from ordinary to "fast" sound. The study of this transition as function of temperature and frequency has made possible to relate this phenomenon to a structural relaxation process, which shows many analogies with the glass-forming systems [8,24].…”

Section: Early Theoretical Models and Recent Experimental Evidences Omentioning

confidence: 99%

Mesoscopic collective dynamics in liquids and the Dual Model

Peluso

2021

Preprint

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In the present article it is shown how a series of experimental evidences and theoretical developments on liquid modelling, gathered for the first time, can all be framed in a mesoscopic view of liquids that are hypothesized as constituted by a population of wave packets, responsible for the propagation of elastic and thermal perturbations, and of dynamic aggregates of molecules, in continuous re-arrangement, diving in an ocean of amorphous, disordered liquid. This model, dubbed Dual Model of Liquids, is complementary to the Phonon theory of Liquid Thermodynamics, recently proposed by an independent group. The pseudo-crystalline dynamic structures, whose presence in liquids is evidenced by high energy inelastic scattering experiments, interact with a statistical population of harmonic elastic waves and anharmonic wave-packets propagating within and among the structures themselves, respectively. The expression for the interaction term is derived from “first principles” based on general considerations related to the pressure exerted by elastic waves travelling in condensed media. The anharmonic character of the interaction allows the exchange not only of energy but also of momentum between wave packets and clusters, thus determining both the displacement of the latter within the medium, and the redistribution of the energy between external, or translatory degrees of freedom of the clusters, and internal collective, vibratory degrees. Using these concepts it is possible to calculate some dynamic and thermodynamic quantities concerning the dynamics of liquids. Moreover, the interpretation of the relaxation times of the processes involved in momentum and energy transport is given, their Order-of-Magnitude is calculated, and the way in which these times are involved in the different phases of the collective dynamics of liquids is discussed. A comparison is provided with results obtained in the frame of PLT and with the forecasts for the visco-elastic transition regions. In the last part of the paper, some experiments are suggested that should be performed to provide additional details to the model.

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Mesoscopic Collective Dynamics in Liquids and the Dual Model

Peluso¹

2022

Journal of Heat Transfer

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A microscopic vision is presented of a Dual Model of Liquids starting from a solid picture. The task is accomplished firstly by showing how a series of experimental evidences and theoretical developments, gathered for the first time, can be framed in a mesoscopic view of liquids, hypothesized as constituted by a population of dynamic aggregates of molecules diving in an ocean of amorphous liquid. The pseudo-crystals interact with the rest of the liquid through harmonic waves and anharmonic wavepackets propagating within and among the structures. The interaction term is derived from "first principles"; its anharmonic character allows the exchange of energy and momentum between the wave packets and the molecule' clusters, determining the displacement of the latter within the medium and the redistribution of the energy between external degrees of freedom (DoF) and internal collective degrees. Among the novelties is that it allows calculating various thermophysical quantities by introducing the statistical number of excited DoF. In this way, the problem is bypassed of other dual models which are sometimes unable to correctly reproduce those thermophysical quantities showing deviations due to the activation/deactivation of internal DoF. The interpretation of the relaxation times is given, their Order-of-Magnitude calculated and compared with experimental data. A comparison is provided with results obtained in the frame of the Phonon theory of Liquid Thermodynamics, as well with systems exhibiting k-gap.In the last part of the paper theoretical insights and experiments are suggested as potential directions for future research and developments.

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Inelastic X-Ray Scattering as a Probe of the Transition Between the Hydrodynamic and the Single Particle Regimes in Simple Fluids

Cited by 8 publications

References 36 publications

Isochoric specific heat in the Dual Model of Liquids and comparison with the Phonon theory of Liquid Thermodynamics

Isochoric specific heat in the Dual Model of Liquids and comparison with the Phonon theory of Liquid Thermodynamics

Mesoscopic collective dynamics in liquids and the Dual Model

Mesoscopic Collective Dynamics in Liquids and the Dual Model

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