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Ciclo de Seminarios 2012

2012 23 OCT

Martes 23 de Octubre
15:00 hs. - Auditorio Emma Pérez Ferreira
Edificio TANDAR
"Glass transitions and critical points in orientationally disordered crystals and structural glassformers: («Strong» liquids are more interesting than we thought)"
C. Austen Angell (*)
Dept. of Chemistry and Biochemistry, Arizona State Univ., Tempe, USA.
RESUMEN: When liquids are classified using Tg-scaled plots of relaxation times (or relative rates of entropy increase above Tg) across a "strong-fragile" spectrum of behaviors, the "strong" liquids have always appeared quite uninteresting(1,2). Here we use updated plots of the same type for crystal phases of the "rotator" variety(3) to confirm that the same pattern of behavior exists for these simpler (center of mass ordered) systems but that now we can show that the "strong" systems owe their behavior to the existence of lambda-type order-disorder transitions at higher temperatures that can be observed when observations are not interrupted by melting. Furthermore, the same observation can be made for systems in which the ordering arrested at the glass transition occurs in the ground state of the system. This prompts an enquiry into the behavior of strong liquids at high temperatures, and we find again evidence for a lambda transition at high temperatures but now it is identifiable as a liquid-liquid critical point of the type suggested for supercooled water. The ramifications of this conclusion will be explored to establish a "big picture"(2) of the relation of thermodynamic transitions to supercooled liquid phenomenology(4,5).
  1. C. A. Angell, J. Non-Cryst. Solids 354, 4703 (2008).
  2. C. A. Angell, MRS Bulletin 33, 545 (2008).
  3. T. Bauer, M. Köhler, P. Lunkenheimer, A. Loidl, C. A. Angell, J. Chem. Phys. 133, 144509 (2010).
  4. D. V. Matyushov, C. A. Angell, J. Chem. Phys. 126, 094501 (2007).
  5. C. A. Angell, in Structural Glasses and Supercooled Liquids: Theory, Experiment, and Applications, First Edition. V. Lubchenko and P. G. Wolynes, Eds. (John Wiley & Sons, Inc., London, 2012).

* El Prof. C. Austen Angell nació en Australia, donde estudió Química Metalúrgica en la Universidad de Melbourne. Obtuvo su PhD en Química en el Imperial College de Londres y luego de un paso por el Argonne National Laboratory se estableció, en 1966, en la Universidad de Purdue. En 1989 pasó a Arizona State University donde es actualmente Regent's Professor of Chemistry and Biochemistry en el Departamento de Química y Bioquímica. Ha publicado más de 500 trabajos (indice h=80), 25 de ellos en Nature y Science, y ha dirigido mas de 40 tesis doctorales. Las principales áreas de interés científico incluyen las propiedades estructurales y de transporte en líquidos, con énfasis en metaestabilidad (sobreenfriados, sobrepresurizados), propiedades de sistemas vítreos, estabilidad de materiales cristalinos y síntesis y caracterización de nuevos materiales para aplicaciones en sistemas electroquímicos de generación de energía. Entre las numerosas distinciones recibidas se destacan: NSF Special Creativity Awards (1985 y 1994); Hildebrand Award (Am. Chem. Soc., 2004), Humboldt Senior Research Fellowship (Alemania, 2004); Outstanding Reviewer Award (Am. Phys. Soc. 2009); Bredig Award (Electrochem. Soc., 2010).
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