LOOKING AT THE GLASS TRANSITION: CHALLENGES OF EXTREME TIME SCALES AND OTHER INTERESTING PROBLEMS

2020 ◽  
Vol 93 (1) ◽  
pp. 79-120 ◽  
Author(s):  
Gregory B. McKenna
Keyword(s):  
Glass Transition ◽  
Time Scales ◽  
Finite Temperature ◽  
Glassy State ◽  
Metastable Equilibrium ◽  
Arrhenius Behavior ◽  
Fictive Temperature ◽  
Major Question ◽  
Kauzmann Temperature ◽  
Glass Forming

ABSTRACT The behavior of glass-forming materials is examined with emphasis on the below-glass transition behavior. A major question that is related to the super-Arrhenius behavior of the dynamics of glass-forming systems is whether the apparent divergence at finite temperature continues below the kinetic or laboratory glass transition that is related to the limits of measurement and is standardized so that the material relaxation time is near 100 s. The problem arises because as the temperature decreases, the time scales required to reach equilibrium (or metastable equilibrium) become geologically long. Yet the apparent finite temperature divergence is fundamental to many theories of glasses; therefore, it becomes essential to find ways to finesse the extreme time scales related to the so-called Kauzmann paradox to bring new information to the ongoing conversation concerning the existence or not of an ideal glass transition at either the Kauzmann temperature or the Vogel–Fulcher–Tammann temperature. After describing the framework of the glassy state that is formed by the early ideas of a fictive temperature, we examine the use of extremely low fictive temperature glasses as a means to potentially get around the long time-scale problem. The challenge is to find ways to create such glasses and measure their properties. In addition to looking at the dynamic behavior of a 20-million-year-old amber and a vapor-deposited amorphous perfluoropolymer whose fictive temperature was the same as the Kauzmann temperature for the material, we also examine the possibility of directly testing the thermodynamics of an ideal glass transition by making athermal solutions of a poly(α-methyl styrene) and its pentamer, where we find that the entropy surface determined from extrapolation of the heat capacity to zero pentamer shows no distinct transition at as much as 180 K below the Kauzmann temperature. The significance of the dynamics of the stable glasses and the thermodynamics of the polymer solutions is discussed in terms that challenge the idea of an ideal glass transition. We also look in more detail at the ability to use vapor deposition to make ethylbenzene, a small-molecule organic, into an ultra-stable glass with a fictive temperature that is possibly below the Kauzmann temperature of this material. We end with remarks on the question of decoupling of different relaxation mechanisms as something not treated by current theories of glass, and we consider some open questions related to the fact that the glass transition remains an unresolved and important problem.

scholarly journals Testing the paradigm of an ideal glass transition: Dynamics of an ultrastable polymeric glass

2018 ◽  
Vol 4 (12) ◽  
pp. eaau5423 ◽  
Author(s):  
Heedong Yoon ◽  
Gregory B. McKenna
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glassy State ◽  
Relaxation Times ◽  
Fictive Temperature ◽  
Transition Dynamics ◽  
Kauzmann Temperature ◽  
Glass Forming ◽  
Equilibrium Data ◽  
Glass Forming Materials

A major challenge to understanding glass-forming materials is obtaining equilibrium data far below the laboratory glass transition temperatureTg. The challenge arises because it takes geologic aging times to achieve the equilibrium glassy state when temperatures are well belowTg. Here, we finesse this problem through measurements on an ultrastable amorphous Teflon with fictive temperatureTfnear to its Kauzmann temperatureTK. In the window betweenTfandTg, the material has a lower molecular mobility than the equilibrium state because of its low specific volume and enthalpy. Our measurements show that the determined scaled relaxation times deviate strongly from the classical expectation of divergence of time scales at a finite temperature. The results challenge the view of an ideal glass transition at or near toTK.

scholarly journals Physical Aging Behavior of a Glassy Polyether

Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 954
Author(s):  
Xavier Monnier ◽  
Sara Marina ◽  
Xabier Lopez de Pariza ◽  
Haritz Sardón ◽  
Jaime Martin ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Physical Aging ◽  
Glassy State ◽  
Aging Behavior ◽  
Scanning Calorimetry ◽  
Narrow Temperature Range ◽  
Glass Forming ◽  
Fast Scanning Calorimetry

The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state.

scholarly journals Observation of an apparent first-order glass transition in ultrafragile Pt–Cu–P bulk metallic glasses

2020 ◽  
Vol 117 (6) ◽  
pp. 2779-2787 ◽  
Author(s):  
Jong H. Na ◽  
Sydney L. Corona ◽  
Andrew Hoff ◽  
William L. Johnson
Keyword(s):  
Glass Transition ◽  
Configurational Entropy ◽  
Freezing Temperature ◽  
Thin Wall ◽  
First Order ◽  
Cu Content ◽  
Kauzmann Temperature ◽  
Entropy Of Fusion ◽  
Glass Forming ◽  
Third Law Of Thermodynamics

An experimental study of the configurational thermodynamics for a series of near-eutectic Pt80-xCuxP20 bulk metallic glass-forming alloys is reported where 14 < x < 27. The undercooled liquid alloys exhibit very high fragility that increases as x decreases, resulting in an increasingly sharp glass transition. With decreasing x, the extrapolated Kauzmann temperature of the liquid, TK, becomes indistinguishable from the conventionally defined glass transition temperature, Tg. For x < 17, the observed liquid configurational enthalpy vs. T displays a marked discontinuous drop or latent heat at a well-defined freezing temperature, Tgm. The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. Below Tgm, the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids at x = 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.

Non-Random Mixing and Fast ion Decoupling in Lithium Chloroborate Superionic Glasses: An Ion Dynamics Computer Simulation Study

1988 ◽  
Vol 135 ◽  
Author(s):  
R. Syed ◽  
J. Kieffer ◽  
C.A. Angell
Keyword(s):  
Glass Transition ◽  
Glassy State ◽  
Laboratory Data ◽  
Mixing Enthalpy ◽  
Transport Numbers ◽  
Ion Dynamics ◽  
Fictive Temperature ◽  
Chemical Ordering ◽  
Pair Potentials ◽  
Ideal Mixing

AbstractLi+ ions are highly mobile in LiCl-Li2O·2B23 glasses to the extent that the decou-pling of conductive modes of motion from the viscous modes, assessed at the glass transition temperature Tg by a relaxation time ratio, is one of the greatest known. The interpretation of the structure of this glass system and its relation to conductivity decoupling is not very advanced at this time but there seems to be a distinction drawn between the chloroborate structure and the structure of the corresponding AgCl-Ag borate and AgI-borate glasses. The latter have frequently been discussed in terms of α-AgI percolating clusters although the available thermodynamic evidence indicates chemical ordering (negative deviations from ideal mixing) as opposed to any sort of clustering (positive deviations from ideal mixing). The LiCl-Li2O-B2O3 system is interesting to us because simple transferable effective pair potentials are available for all species in the system and ion dynamics computer simulations should be capable of giving useful insights into the structure, energetics, and dynamics of the system. We present diffusivity data as a function of temperature for several compositions in the LiClLi2O·2B2O3 system and observe that the Li+ mobility remains high below the simulated, glass transition. Surprisingly, the Cl− anion mobility also remains high, raising a question about anion transport numbers in these glasses. Computed conductivities agree with laboratory data in the liquid state but exceed laboratory data in the glassy state in the direction expected from the high fictive temperature of simulated glass. Deviations from additivity in mixing energy in this system show a weak tendency to clustering of LiCl in the structure which suggests a need for laboratory mixing enthalpy studies.

Equilibrium Thermodynamics Near the Glass Transition - The Conceptual Application of the Limiting Fictive Temperature

1998 ◽  
Vol 554 ◽  
Author(s):  
G. Wilde ◽  
J. H. Perepezko
Keyword(s):  
Glass Transition ◽  
Shear Viscosity ◽  
Glass Temperature ◽  
Bulk Glass ◽  
Equilibrium Thermodynamics ◽  
Fictive Temperature ◽  
Glass Forming ◽  
Valid Comparison ◽  
Undercooled Melt ◽  
Stability Limits

AbstractThe enthalpy, entropy, specific heat, specific volume and the equilibrium shear viscosity of the deeply undercooled melt of the bulk glass forming alloy Pd40Ni40P20 have been determined as functions of temperature. The concept of limiting fictive temperature was applied to the entire set of measurements in order to allow for a valid comparison of the data based upon the respective equilibrium values. The comparison of the equilibrium properties shows that a proposed hierarchy of stability limits does not apply for this alloy. The results also indicate that the glass temperature as defined by the limiting fictive temperature does not depend on the property under observation.

scholarly journals Is not it time to go back to Tg Tamman?

2016 ◽  
Vol 19 (2) ◽  
pp. 133-144
Author(s):  
V. S. Minaev ◽  
N. M. Parfenov ◽  
S. P. Timoshenkov ◽  
V. P. Vassiliev ◽  
V. V. Kalugin ◽  
...  
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Chemical Nature ◽  
Glassy State ◽  
Temperature Curve ◽  
Reverse Direction ◽  
Glass Forming ◽  
Physico Chemical ◽  
Numerous Experimental Data ◽  
Heated Glass

Based on the analysis of numerous experimental data shows that the generally accepted today, the glass transition temperatureTg is not. It was the result of borrowing from tammana symbolTg, is meant the temperature of viscous flow liquid transformation into solid brittle glassy state, and use it together symbolTw, means the temperature tammana bend on the dependence of the «property-temperature» glass-forming substances aboveTg of tammana. On the basis of the application of polymer-polymorphing representations of the structure of glass-forming substances are disclosed physico-chemical nature of the temperature curveTw (conventional Segodnya), which is the temperature of the reverse direction interconversion of nanofragments patterns (polymorphical) high and low temperature polymorphs that coexist in the vitreous substance. The discovery in recent decades prezentatsionnogo effect located as tammanaTg, is below the standardTg,Tg confirms the truth of tammana characterized by increasedspecific heat of the heated glass.

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