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SUMMARY:Challenging Paradigms of Glass Formation: The Kauzmann Paradox and
  Diverging Time-Scales - Professor Gregory B. McKenna\, Department of Chem
 ical Engineering\, Texas Tech University
DTSTART:20200220T134500Z
DTEND:20200220T144500Z
UID:TALK139786@talks.cam.ac.uk
CONTACT:Prof. A. L. Greer
DESCRIPTION:There are two important “signatures” related to glass form
 ation. The first is the apparent entropy catastrophe that occurs at the Ka
 uzmann temperature TK where the extrapolated entropy seems to go below tha
 t of the crystal.  A related phenomenon is that the dynamics (relaxation t
 imes) of glass-forming systems seem to extrapolate to a finite temperature
  divergence at the so-called VFT temperature TVFT\, which is often found t
 o be close to TK. Testing the equilibrium response near to these temperatu
 res has become a major challenge in glass physics.  To tackle this problem
 \, we are using materials with extremely low fictive temperature TF relati
 ve to Tg\, entering an unexplored region of the glassy state. First\, we u
 sed of a 20 million year old amber with TF ∼ 43.6 K below Tg.  We found 
 that the relaxation times deviated strongly from the expected VFT or WLF-b
 ehaviors turning towards an Arrhenius-response\, albeit with a high activa
 tion energy. Also\, we built on the ultra-stable glasses ideas exploited b
 y Ediger and co-workers and developed a vapor deposition procedure to make
  an amorphous Teflon material with TF ∼55 K below Tg and close to the pu
 tative TK. Our results challenge the view that there is an "ideal" glass t
 ransition as posited by multiple theories and commonly considered an impor
 tant aspect of glass-formation and glassy behavior.  In addition\, we have
  examined the thermodynamics of the problem by using an athermal mixture o
 f a poly(-methyl styrene) with its own pentamer and show that in this s
 ystem the equilibrium entropies continue smoothly without evidence of a se
 cond order transition to at least 180 K below the Kauzmann temperature.  S
 uch results are consistent with there not being an “ideal” glass trans
 ition and demand reconsideration of theories that use or predict such a th
 ermodynamic point in glass-forming systems.\n\n
LOCATION:Goldsmiths' Lecture Room 1\, Department of Materials Science &amp
 \; Metallurgy\, 27 Charles Babbage Road\, CB3 0FS
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