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Searching for the Ideal Glass Transition: Ultra-stable Glasses and Yotta Second Time-Scales

Gregory B. McKenna, Department of Chemical and Biomolecular Engineering, North Carolina State University Raleigh, NC 20795
 
Where :

Abstract:
In prior work we have addressed the problem of the glass transition by examining the response of ultra-stable glasses in the temperature range between the Kauzmann temperature TK and the glass transition temperature Tg with the constraint that the temperature of test be T>TF where TF is the fictive temperature. In this case, the relaxation time has a value that is greater than that of the equilibrium liquid, thus opening the possibility of testing the idea that the dynamics or the viscosity of the glass-forming liquid diverge as one approaches TK.  In the prior work we had discovered an ancient amber from the Dominican Republic that had a fictive temperature approximately 42.6 K below the Tg and 27.6 K above TK. In that work there was a strong turnover of the relaxation time vs. T or vs. 1/T that showed that the dynamics do not seem to diverge upon cooling towards the Kauzmann temperature, thus challenging the ideas related to an “ideal” glass transition in which such finite temperature divergence of the dynamics is expected. The other important prior work built on that of the Dominican amber and used a vacuum pyrolysis deposition method to create an amorphous Teflon® material having TF≈TK. By using the TTU bubble inflation method we were able to measure the viscoelastic response of the small quantities of material made by the VPD method and found, again, that the dynamics do not diverge as the Kauzmann temperature is approached.  These measurements covered the glassy response over approximately 12 logarithmic decades in time from 102 s to 1014 s, i.e., from hecto seconds to 100 tera seconds. Though these results are consistent with the idea that the ideal glass transition does not exist, or at least that the relaxation times do not diverge, there are still two important questions related to this deep glassy state behavior. One question is can one can make measurements in a condition that is near to the equilibrium state this far below the Tg? I.e, where the test temperature is equal to the fictive temperature and consequently determine the temperature dependence of the equilibrium response rather than an upper bound to this response.  The second question that arises is can one find or create a glass with a fictive temperature that is below the Kauzmann temperature and to then characterize its dynamics?  The questions just posed have an affirmative answer. We have found a different amorphous perfluorocarbon polymer Cytop® for which we have made an ultra-stable material with TF=TK-10 K, suggesting the possibility that ultradense glasses can be made by VPD and opening an avenue to controlled study to extremely deep glassy state materials.  In the other instance, by a true act of serendipity to be described in the presentation, we discovered an ancient amber (Fushun, China, 60 million-years-old) for which TF=278.2 K and Tg=464.2 K, i.e., Tg-TF=186 K. We were able to “de-age” this very low fictive temperature glass and carry out tests at T=TF, i.e., where the dynamics are those of the equilibrium material. We also investigated the window of the upper bound relaxations between TF and Tg. The chief findings are that the equilibrium relaxation time at extremely low temperatures do not diverge and reach 1023 s, i.e., 0.1 yotta seconds (Ys) and the longest relaxation time observed exceeded 102 Ys.  In addition, we find that in the deep glassy state where T>TFthe isothermal relaxation times exhibit only weak volume dependence, but at constant fictive temperature the volume dependence is very strong and form a family of parallel curves.  Finally, the upper bound equilibrium relaxation times near to the Tg show similar behavior to the times seen in the Dominican amber and the ultra-stable amorphous Teflon® but as one goes deeper into the glassy state the response seems to remain exponential with decreasing temperature rather than following an Arrhenius-like temperature dependence.  These results open new avenues for research and understanding of glass-forming materials and the deep glassy state behavior.

Détails

Date :
8 juillet 2022
Heure :
11 h 00 - 12 h 00
Catégorie d’Évènement:

Organisateur

Gregory B. McKenna

Lieu

ESPCI Paris
10 Rue Vauquelin
Paris, 75005 France
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Phone
01 40 79 44 00
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