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      General rules prospected for the liquid fragility in various material groups and different thermodynamic conditions

      1 , 2 , 1 , 2 , 1 , 2 , 1 , 2 , 3 , 1 , 2
      The Journal of Chemical Physics
      AIP Publishing

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          Abstract

          The fragility parameter has been acknowledged as one of the most important characteristics of glass-forming liquids. We show that the mystery of the dramatic change in molecular dynamics of systems approaching the glass transition can be better understood by the high pressure study of fragility parameters defined in different thermodynamic conditions. We formulate and experimentally confirm a few rules obeyed by the fragility parameters, which are also rationalized by the density scaling law and its modification suggested for associated liquids. In this way, we successfully explore and gain a new insight into the pressure effect on molecular dynamics of van der Waals liquids, polymer melts, ionic liquids, and hydrogen-bonded systems near the glass transition.

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          Relaxation in liquids, polymers and plastic crystals — strong/fragile patterns and problems

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            Universal link between the boson peak and transverse phonons in glass.

            The physical properties of a topologically disordered amorphous material (glass), such as heat capacity and thermal conductivity, are markedly different from those of its ordered crystalline counterpart. The understanding of these phenomena is a notoriously complex problem. One of the universal features of disordered glasses is the 'boson peak', which is observed in neutron and Raman scattering experiments. The boson peak is typically ascribed to an excess density of vibrational states. Here, we study the nature of the boson peak, using numerical simulations of several glass-forming systems. We discovered evidence suggestive of the equality of the boson peak frequency to the Ioffe-Regel limit for 'transverse' phonons, above which transverse phonons no longer propagate. Our results indicate a possibility that the origin of the boson peak is transverse vibrational modes associated with defective soft structures in the disordered state. Furthermore, we suggest a possible link between slow structural relaxation and fast boson peak dynamics in glass-forming systems.
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              Poisson's ratio and the fragility of glass-forming liquids.

              The nature of the transformation by which a supercooled liquid 'freezes' to a glass--the glass transition--is a central issue in condensed matter physics but also affects many other fields, including biology. Substantial progress has been made in understanding this phenomenon over the past two decades, yet many key questions remain. In particular, the factors that control the temperature-dependent relaxation and viscous properties of the liquid phase as the glass transition is approached (that is, whether the glass-forming liquid is 'fragile' or 'strong') remain unclear. Here we show that the fragility of a glass-forming liquid is intimately linked to a very basic property of the corresponding glass phase: the relative strength of shear and bulk moduli, or Poisson's ratio.
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                Author and article information

                Journal
                The Journal of Chemical Physics
                The Journal of Chemical Physics
                AIP Publishing
                0021-9606
                1089-7690
                October 07 2014
                October 07 2014
                : 141
                : 13
                : 134507
                Affiliations
                [1 ]Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland
                [2 ]Silesian Center for Education and Interdisciplinary Research, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland
                [3 ]Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, D-01069 Dresden, Germany
                Article
                10.1063/1.4897208
                25296821
                21344bb7-de12-4038-b4d2-6ff0a8f264de
                © 2014
                History

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