Challenging Paradigms of Glass Formation:
The Kauzmann Paradox and Diverging Time-Scales
by
Gregory B. McKenna
Dept. of Chemical Engineering, Texas Tech University
Lubbock, TX, USA
SEMINAR
Challenging Paradigms of Glass Formation:
The Kauzmann Paradox and Diverging Time-Scales
Gregory B. McKenna
Dept. of Chemical Engineering, Texas Tech University
Lubbock, TX, USA
at
Dept of Materials Science & Metallurgy,
27 Charles Babbage Road, CB3 0FS
Goldsmiths’ Lecture Room 1
Thursday 20 February 2020, 13:45-14:45pm
There are two important “signatures” related to glass formation. The first is the apparent entropy catastrophe that occurs at the Kauzmann temperature TK where the extrapolated entropy seems to go below that of the crystal. A related phenomenon is that the dynamics (relaxation times) of glass-forming systems seem to extrapolate to a finite temperature divergence at the so-called VFT temperature TVFT, which is often found to be close to TK. Testing the equilibrium response near to these temperatures has become a major challenge in glass physics. To tackle this problem, we are using materials with extremely low fictive temperature TF relative to Tg, entering an unexplored region of the glassy state. First, we used 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-behaviors turning towards an Arrhenius-response, albeit with a high activation energy. Also, we built on the ultra-stable glasses ideas exploited by 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 putative TK. Our results challenge the view that there is an "ideal" glass transition as posited by multiple theories and commonly considered an important aspect of glass-formation and glassy behavior. In addition, we have examined the thermodynamics of the problem by using an athermal mixture of a poly(a-methyl styrene) with its own pentamer and show that in this system the equilibrium entropies continue smoothly without evidence of a second order transition to at least 180 K below the Kauzmann temperature. Such results are consistent with there not being an “ideal” glass transition and demand reconsideration of theories that use or predict such a thermodynamic point in glass-forming systems.
Gregory B. McKenna. Brief Biographical Description
Gregory B. McKenna attended the U.S. Air Force Academy from which he received his Bachelor’s degree in Engineering Mechanics in 1970. As part of his active duty he attended MIT where he earned a Masters Degree in the area of composite materials before being stationed at Hill Air Force Base in Ogden Utah, where he served as a Test Evaluation Engineer until 1975 when he left the Air Force at the rank of Captain. While in Utah, he also obtained a Ph.D. in Materials Science and Engineering at the University of Utah, graduating in 1976. Dr. McKenna was honored with a National Research Council Postdoc at the then National Bureau of Standards (NBS) and accepted a permanent position at NBS (now NIST) in 1977. He was the head of the Structure and Mechanics Group in the Polymers Division at NIST from August 1992 until July 1999 when he moved to Texas Tech University as Professor in the Department of Chemical Engineering and John R. Bradford Endowed Chair in Engineering. In 2005 he became a Paul Whitfield Horn Professor at TTU. Dr. McKenna has earned a reputation as a pioneering researcher in multiple areas of polymers and materials physics and engineering, including physics of glasses, solid mechanics and nonlinear viscoelasticity of polymers, thermodynamics and mechanics of elastomers and gels, and molecular rheology. He has over 235 publications that have been cited over 16,500 times. Dr. McKenna is a Fellow of the American Physical Society, the Society of Plastics Engineers, the Society of Engineering Science, the North American Thermal Analysis Society (NATAS), The American Institute of Chemical Engineers, and the American Association for the Advancement of Science (AAAS). He is the recipient of multiple awards including the International Award from the Society of Plastics Engineers, the Mettler-Toledo Award of NATAS, and the Bingham Medal of the Society of Rheology. He has served as Chairman of the Polymer Physics Division of the APS, President of the Society of Engineering Science, and President of the Society of Rheology.