Organic Glasses and Polymers

Rössler, E. A.; Sillescu, H.

doi:10.1002/9783527603978.mst0100

Cited by 4 publications

(5 citation statements)

References 115 publications

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“…Table 1). Experimentally, one often observes that T c / T g ≃ 1.2 40. We rather find that T c / T g ≃ 1.03 or even T c / T g ≃ 1, if T i is identified with T g .…”

Section: Resultsmentioning

confidence: 54%

Thickness‐dependent reduction of the glass‐transition temperature in thin polymer films with a free surface

Peter¹,

Meyer²,

Baschnagel³

2006

J Polym Sci B Polym Phys

192

226

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We present results of molecular dynamics simulations for free-standing and supported thin films of a nonentangled polymer melt using a coarse-grained (beadspring) model. Our discussion is mainly concerned with the equilibrium properties of the films above the critical temperature (T c ) of mode-coupling theory, although we also determine the glass-transition temperature (T g ) by measurements of the film thickness h upon cooling. We explore the influence of confinement on the structure and dynamics of the polymer films. We find that the dynamics in the films is accelerated compared to the bulk, that this enhanced mobility originates from the surfaces, and that the effect is larger at the free than at the supported surface. Thus, the films have lower T c values relative to the bulk. T c depends on film thickness h; this dependence can be well parametrized by T c (h) = T bulk c /(1 + h 0 /h), a function proposed by experiments on supported polystyrene films.

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“…Table 1). Experimentally, one often observes that T c / T g ≃ 1.2 40. We rather find that T c / T g ≃ 1.03 or even T c / T g ≃ 1, if T i is identified with T g .…”

Section: Resultsmentioning

confidence: 54%

Thickness‐dependent reduction of the glass‐transition temperature in thin polymer films with a free surface

Peter¹,

Meyer²,

Baschnagel³

2006

J Polym Sci B Polym Phys

192

226

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“…Ideal MCT predicts a complete structural arrest at T c . A freezing at T c is not observed experimentally [21,150]. (An exception is possibly provided by hard sphere-like colloidal suspensions [128].)…”

Section: 31mentioning

confidence: 97%

Computer simulations of supercooled polymer melts in the bulk and in confined geometry

Baschnagel

Varnik

2005

J. Phys.: Condens. Matter

352

578

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We survey results of computer simulations for the structure and dynamics of supercooled polymer melts and films. Our survey is mainly concerned with features of a coarse grained polymer model-a bead-spring model-in the temperature regime above the critical glass temperature T c of the ideal modecoupling theory (MCT). We divide our discussion into two parts: a part devoted to bulk properties and a part dealing with thin films. The discussion of the bulk properties focuses on two aspects: a comparison of the simulation results with MCT and an analysis of dynamic heterogeneities. We explain in detail how the analyses are performed and what results may be obtained, and we critically assess their strengths and weaknesses. In discussing the application of MCT we also present first results of a quantitative comparison which does not rely on fits, but exploits static input from the simulation to predict the relaxation dynamics. The second part of this review is devoted to extensions of the simulations from the bulk to thin films. We explore in detail the influence of the boundary condition, imposed by smooth or rough walls, on the structure and dynamics of the polymer melt. Geometric confinement is found to shift the glass transition temperature T g (or T c in our case) relative to the bulk. We compare our and other simulation results for the T g shift with experimental data, briefly survey some theoretical ideas for explaining these shifts and discuss related simulation work on the glass transition of confined liquids. Finally, we also present some technical details of how to perform fits to MCT and give a brief introduction to another approach to the glass transition based on the potential energy landscape of a liquid.

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“…Therefore, a liquid that is cooled sufficiently quickly through T l , may bypass crystallization and be 'super-cooled' to a state of metastable equilibrium at temperatures beneath the melting point. As the temperature of the supercooled liquid drops further, its viscosity begins to increase dramatically, by as much as 16 decades over a temperature interval as small as a few hundred Kelvin (this is very clearly demonstrated by the behavior o-terphenyl [15] and many other "fragile" [16,17] glass formers). Eventually, a "glass transition" temperature (T g ) is reached where the viscosity is so large that molecular rearrangements cease on physically meaningful timescales, and the supercooled liquid is termed a glass.…”

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confidence: 99%

Critical assessment of the equilibrium melting-based, energy distribution theory of supercooled liquids and application to jammed systems

Weingartner,

Pueblo,

Kelton

et al. 2015

Preprint

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Despite decades of intense study, the mechanisms underlying the extraordinary dynamics of supercooled liquids as they approach the glass transition remain, at best, mis-characterized, and at worst, misunderstood. A long standing endeavor is to understand the remarkable increase of the viscosity with supercooling. Recently, a new theory of supercooled liquids has been proposed that starts from first principles, using elementary statistical mechanics arguments, to derive a form for the viscosity that contains only a single fitting parameter in its simplest form. In this we demonstrate that this exact same form may be derived from a different starting point, and then critically examine its performance. In the process we find that functional form proposed fits the viscosity data of a diverse group of 45 liquids exceptionally well over a wide temperature range, and uncover a number of interesting correlations of the single parameter with various thermodynamic quantities, ultimately allowing for the prediction of low temperature viscosity from high temperature data. Additionally, we find that similar physical reasoning can be used to derive a similar, single parameter form for the viscosity of hardsphere/jammed liquids. We demonstrate that this form accurately reproduces the viscosity of hard-spheres, suggesting an underlying universality in metastable dynamics.

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Organic Glasses and Polymers

Cited by 4 publications

References 115 publications

Thickness‐dependent reduction of the glass‐transition temperature in thin polymer films with a free surface

Thickness‐dependent reduction of the glass‐transition temperature in thin polymer films with a free surface

Computer simulations of supercooled polymer melts in the bulk and in confined geometry

Critical assessment of the equilibrium melting-based, energy distribution theory of supercooled liquids and application to jammed systems

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