scholarly journals Dissecting Dynamics near the Glass Transition

2021 ◽  
Author(s):  
Khalil Akkaoui ◽  
Joe Schlenoff
Keyword(s):  
Glass Transition ◽  
Arrhenius Equation ◽  
Molecular Level ◽  
Simple Expression ◽  
Polyelectrolyte Complexes ◽  
Glass Forming ◽  
Repeat Units ◽  
Charged Polymers ◽  
Glass Forming Materials ◽  
Selection Of

Abstract Though the strong transformation in mechanical properties of glass-forming materials near the glass transition, Tg, has been recognized and exploited for millenia, efforts to understand and predict this phenomenon at a molecular level continue to this day. Close to Tg, where relaxation is considerably slower than predicted by the well-known Arrhenius equation, one of the most versatile and widely-used expressions to describe the dynamics or relaxation of glass formers is that of Vogel, Fulcher and Tammann (VFT). The VFT equation, introduced nearly 100 years ago, contains three adjustable fit parameters. In this work the dynamics of the polymer repeat units are related to macroscopic dynamics in polyelectrolyte complexes, which are hydrated amorphous blends of charged polymers. A simple expression, containing no freely adjustable fit parameters, is derived to quantitatively model relaxation from Tg to temperatures well into the Arrhenius region. The new expression, which also fits a selection of three common neutral polymers, will advance the understanding and use of the glass-forming phenomenon.

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.

Correlation Between Thermodynamic and Kinetic Properties of Glass-Forming Liquids

2007 ◽  
Vol 1048 ◽  
Author(s):  
Oleg N. Senkov ◽  
Daniel B. Miracle
Keyword(s):  
Glass Transition ◽  
Geometric Mean ◽  
Configurational Entropy ◽  
Excess Heat Capacity ◽  
Kinetic Properties ◽  
Vibrational Entropy ◽  
Glass Forming ◽  
Characteristic Temperatures ◽  
Higher Temperature ◽  
Glass Forming Materials

AbstractCorrelations between three characteristic temperatures: glass transition, Tg, Kauzmann, Tk, and Vogel-Fulcher-Tammann, To, were identified from the analysis of more than 60 metallic and non-metallic glass-forming materials. It was found that Tg ≥ Tk ≥ To and Tk is the geometric mean of Tg and To. The relation Tk ≥ To indicates that the excess total entropy of a super-cooled liquid ΔS approaches zero at a higher temperature than the configurational entropy ΔSconf, and such behavior was explained by the stronger temperature dependence of the excess vibrational entropy of the liquid, ΔSvib, than that of the corresponding glass, . A relationship between the fragility index m, reduced excess heat capacity ΔCp(Tg)/Sm, and reduced glass transition temperature, Trg, was identified using the found correlation between the characteristic temperatures.

scholarly journals Electron anions and the glass transition temperature

2016 ◽  
Vol 113 (36) ◽  
pp. 10007-10012 ◽  
Author(s):  
Lewis E. Johnson ◽  
Peter V. Sushko ◽  
Yudai Tomota ◽  
Hideo Hosono
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Control Parameter ◽  
Computational Study ◽  
Amorphous Material ◽  
Materials Design ◽  
Spectroscopic Properties ◽  
Glass Forming ◽  
Selection Of

Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca12Al14O32]2+ ⋅ (e–)2, we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design.

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.

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