Role of the density in the crossover region of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>o</mml:mi></mml:mrow></mml:math>‐terphenyl and poly(vinyl acetate)

Barbieri, A.; Gorini, G.; Leporini, Dino

doi:10.1103/physreve.69.061509

Cited by 33 publications

(33 citation statements)

References 52 publications

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“…It was concluded that the proper inclusion of many-body static correlations in theories of the glass transition appears crucial for the description of the dynamics of fragile glass formers [56]. The search of a link between structural ordering and slow dynamics motivated several studies in liquids [57][58][59][60][61], colloids [62][63][64] and polymeric systems [62,[65][66][67][68][69][70]. We also note that the elastic models of the glass transition conclude that the relaxation is related to the elastic shear modulus, a quantity which is set by the arrangement of the particles in mechanical equilibrium and their mutual interactions [9,39].…”

Section: Introductionmentioning

confidence: 99%

Weak links between fast mobility and local structure in molecular and atomic liquids

Bernini

Puosi

Leporini

2015

The Journal of Chemical Physics

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We investigate by Molecular-Dynamics simulations the fast mobility -the rattling amplitude of the particles temporarily trapped by the cage of the neighbors -in mildly supercooled states of dense molecular (linear trimers) and atomic (binary mixtures) liquids. The mixture particles interact by the Lennard-Jones potential. The non-bonded particles of the molecular system are coupled by the more general Mie potential with variable repulsive and attractive exponents in a range which is characteristic of small n-alkanes and n-alcohols. Possible links between the fast mobility and the geometry of the cage (size and shape) are searched. The correlations on a per-particle basis are rather weak. Instead, if one groups either the particles in fast-mobility subsets or the cages in geometric subsets, the increase of the fast mobility with both the size and the asphericity of the cage is revealed. The observed correlations are weak and differ in states with equal relaxation time. Local forces between a tagged particle and the first-neighbour shell do not correlate with the fast mobility in the molecular liquid. It is concluded that the cage geometry alone is unable to provide a microscopic interpretation of the known, universal link between the fast mobility and the slow structural relaxation. We suggest that the particle fast dynamics is affected by regions beyond the first neighbours, thus supporting the presence of collective, extended fast modes.

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Section: Introductionmentioning

confidence: 99%

Weak links between fast mobility and local structure in molecular and atomic liquids

Bernini

Puosi

Leporini

2015

The Journal of Chemical Physics

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“…This includes the Adam-Gibbs derivation of the structural relaxation [7,8] built on the thermodynamic notion of the configurational entropy [9] -, the mode-coupling theory [10] and extensions [11], the random first-order transition theory (RFOT) [12], the frustrationbased approach [13], as well as the so-called elastic models [14,15]. The search of a link between structural ordering and slow dynamics motivated several studies in liquids [16][17][18][19], colloids [20][21][22] and polymeric systems [20,[23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Cage rattling does not correlate with the local geometry in molecular liquids

Bernini

Puosi

Leporini

2015

Journal of Non-Crystalline Solids

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Molecular-dynamics simulations of a liquid of short linear molecules have been performed to investigate the correlation between the particle dynamics in the cage of the neighbors and the local geometry. The latter is characterized in terms of the size and the asphericity of the Voronoi polyhedra. The correlation is found to be poor. In particular, in spite of the different Voronoi volume around the end and the inner monomers of a molecule, all the monomers exhibit coinciding displacement distribution when they are caged (as well as at longer times during the structural relaxation). It is concluded that the fast dynamics during the cage trapping is a non-local collective process involving monomers beyond the nearest neighbours.PACS numbers:

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“…Some find that temperature dominates glassy dynamics by far [6,7,8,9]; some that it does not [10,11,12]. Others find both variables to exert equal influence [13,14,15,16,17,18,19,20,21,22], some with temperature [23,24,25,26,27], some with density ̺ being more relevant [28,29,30,31]. The difficulty of obtaining data over wide pressure ranges might be impeding: few studies, pioneered only in the 1990's [28,32], go beyond 1 GPa.…”

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Idealized Glass Transitions under Pressure: Dynamics versus Thermodynamics

Voigtmann

2008

Phys. Rev. Lett.

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The interplay of slow dynamics and thermodynamic features of dense liquids is studied by examinining how the glass transition changes depending on the presence or absence of Lennard-Jones-like attractions. Quite different thermodynamic behavior leaves the dynamics unchanged, with important consequences for high-pressure experiments on glassy liquids. Numerical results are obtained within mode-coupling theory (MCT), but the qualitative features are argued to hold more generally. A simple square-well model can be used to explain generic features found in experiment. The quest for identifying the physical mechanism behind the dynamical transformation of a liquid into an amorphous solid, the glass transition, has prompted many studies aiming to disentangle the dominant control variables involved. It is recognized that the slow dynamics connected with the glass transition is universal, but its connection to the underlying liquid structure is highly debated [1,2,3,4,5]. Some argue in terms of a density effect called free or excluded volume; others attribute the main physics to energetic interactions and thermally activated processes.Experiments changing both temperature T and pressure P close to the transition are emerging to resolve such issues, but have brought contradictory results. Some find that temperature dominates glassy dynamics by far [6,7,8,9]; some that it does not [10,11,12]. Others find both variables to exert equal influence [13,14,15,16,17,18,19,20,21,22], some with temperature [23,24,25,26,27], some with density ̺ being more relevant [28,29,30,31]. The difficulty of obtaining data over wide pressure ranges might be impeding: few studies, pioneered only in the 1990's [28,32], go beyond 1 GPa.Here we propose that to resolve the apparent contradictions, one needs to separate non-universal thermodynamic aspects, namely the equation of state (EOS) of the system, from universal dynamical features, viz. the slow relaxation. Specifically, we show how the presence or absence of attractive interactions affects the glass transition, and how this emerges in different pairs of variables linked by the EOS: (̺, T ) (preferred by theory) vs. (P, T ) (more amenable to experiments), yielding a transition that appears 'temperature-driven' in the latter.The Lennard-Jones (LJ) potential serves as a realistic interaction model: V LJ (r) = 4ǫ[(r/σ) −12 −(r/σ) −6 ], with dimensionless parameters ̺ * = ̺σ 3 , T * = 1/(βǫ), P * = P σ 3 /ǫ; β = 1/(k B T ) with Boltzmann's constant k B . To study relative effects of entropy and energy, we compare the LJ glass transition with that of its purely repulsive (LJR) counterpart, V LJR (r) = V LJ (r) + ǫ ≥ 0 for r ≤ 2 1/6 σ, V LJR (r) = 0 else. For the transition lines, modecoupling theory (MCT) [33,34] provides a reasonable qualitative description. Its transition temperature T c is systematically above the experimental (calorimetric) one, T g , but nevertheless serves as a good indicator for the change from high-T liquid-like dynamics to low-T glasslike one [35,36]. In MCT, T c is the...

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Role of the density in the crossover region ofo‐terphenyl and poly(vinyl acetate)

Cited by 33 publications

References 52 publications

Weak links between fast mobility and local structure in molecular and atomic liquids

Weak links between fast mobility and local structure in molecular and atomic liquids

Cage rattling does not correlate with the local geometry in molecular liquids

Idealized Glass Transitions under Pressure: Dynamics versus Thermodynamics

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