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.

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.

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 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.

A glass transition due to freezing-in of positional disorder of mobile silver ions in the glassy state of the AgBrAgPO3 system

1995 ◽  
Vol 266 ◽  
pp. 79-95 ◽  
Author(s):  
Minoru Hanaya ◽  
Tomoyasu Okubayashi ◽  
Toshio Sakurai ◽  
Masaharu Oguni
Keyword(s):  
Glass Transition ◽  
Glassy State ◽  
Silver Ions ◽  
Positional Disorder

scholarly journals Physical state of 2-methylbutane-1,2,3,4-tetraol in pure and internally mixed aerosols

2018 ◽  
Vol 18 (21) ◽  
pp. 15841-15857 ◽  
Author(s):  
Jörn Lessmeier ◽  
Hans Peter Dette ◽  
Adelheid Godt ◽  
Thomas Koop
Keyword(s):  
Glass Transition ◽  
Relative Humidity ◽  
Oxidation Product ◽  
Secondary Organic Aerosols ◽  
Glassy State ◽  
Organic Aerosols ◽  
Lower Troposphere ◽  
Tropospheric Temperature ◽  
Transition Temperatures ◽  
Glass Transition Temperatures

Abstract. 2-Methylbutane-1,2,3,4-tetraol (hereafter named tetraol) is an important oxidation product of isoprene and can be considered as a marker compound for isoprene-derived secondary organic aerosols (SOAs). Little is known about this compound's physical phase state, although some field observations indicate that isoprene-derived secondary organic aerosols in the tropics tend to be in a liquid rather than a solid state. To gain more knowledge about the possible phase states of tetraol and of tetraol-containing SOA particles, we synthesized tetraol as racemates as well as enantiomerically enriched materials. Subsequently the obtained highly viscous dry liquids were investigated calorimetrically by differential scanning calorimetry revealing subambient glass transition temperatures Tg. We also show that only the diastereomeric isomers differ in their Tg values, albeit only by a few kelvin. We derive the phase diagram of water–tetraol mixtures over the whole tropospheric temperature and humidity range from determining glass transition temperatures and ice melting temperatures of aqueous tetraol mixtures. We also investigated how water diffuses into a sample of dry tetraol. We show that upon water uptake two homogeneous liquid domains form that are separated by a sharp, locally constrained concentration gradient. Finally, we measured the glass transition temperatures of mixtures of tetraol and an important oxidation product of α-pinene-derived SOA: 3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA). Overall, our results imply a liquid-like state of isoprene-derived SOA particles in the lower troposphere at moderate to high relative humidity (RH), but presumably a semisolid or even glassy state at upper tropospheric conditions, particularly at low relative humidity, thus providing experimental support for recent modeling calculations.

scholarly journals Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6509
Author(s):  
Robert F. Tournier ◽  
Michael I. Ojovan
Keyword(s):  
Glass Transition ◽  
Heating Rate ◽  
Homogeneous Nucleation ◽  
Glassy State ◽  
Singular Values ◽  
Md Simulations ◽  
Melting Temperatures ◽  
Heating And Cooling ◽  
Dynamics Simulations ◽  
Universal Law

A second melting temperature occurs at a temperature Tn+ higher than Tm in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to Tn+. Recent MD simulations show full melting at Tn+ = 1.119Tm for Zr, 1.126Tm for Ag, 1.219Tm for Fe and 1.354Tm for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at Tg and the nucleation temperatures TnG of glacial phases are successfully predicted below and above Tm. The glass transition temperature Tg increases with the heating rate up to Tn+. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating Tn+ and TnG around Tm shows that TnG cannot be higher than 1.293Tm for Tn+= 1.47Tm. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with Tg and TnG above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to Tn+ because the antibonds are broken by homogeneous nucleation of bonds.

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