Modification of the Adam−Gibbs Model of Glass Transition for Consistency with Experimental Data

1999 ◽  
Vol 103 (28) ◽  
pp. 5895-5902 ◽  
Author(s):  
K. L. Ngai
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Gibbs Model

scholarly journals CO2 Induced Foaming Behavior of Polystyrene near the Glass Transition

2017 ◽  
Vol 2017 ◽  
pp. 1-15
Author(s):  
Salah Al-Enezi
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Glass Transition ◽  
Dissolved Gas ◽  
Foaming Process ◽  
Foaming Behavior ◽  
Potential Applications ◽  
Model C ◽  
Parameter Values ◽  
Good Agreement

This paper examines the effect of high-pressure carbon dioxide on the foaming process in polystyrene near the glass transition temperature and the foaming was studied using cylindrical high-pressure view cell with two optical windows. This technique has potential applications in the shape foaming of polymers at lower temperatures, dye impregnation, and the foaming of polystyrene. Three sets of experiments were carried out at operating temperatures of 50, 70, and 100°C, each over a range of pressures from 24 to 120 bar. Foaming was not observed when the polymer was initially at conditions below Tg but was observed above Tg. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites, with maximum radius of 0.02–0.83 mm. Three models were applied on the foaming experimental data. Variable diffusivity and viscosity model (Model C) was applied to assess the experimental data with the WLF equation. The model shows very good agreement by using realistic parameter values. The expansion occurs by diffusion of a dissolved gas from the supersaturated polymer envelope into the bubble.

Mean-Field Calculations of the Dynamic Mechanical Properties of Heterogeneous Elastomer Blends

1989 ◽  
Vol 62 (2) ◽  
pp. 305-314 ◽  
Author(s):  
K. A. Mazich ◽  
P. C. Killgoar ◽  
J. A. Ingram
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Glass Transition ◽  
Storage Modulus ◽  
Theoretical Calculations ◽  
Mean Field ◽  
Dynamic Mechanical Properties ◽  
Particle Model ◽  
Dynamic Mechanical ◽  
Grain Model

Abstract A method for calculating the dynamic mechanical properties of elastomer blends with co-continuous structures has been presented. The calculations are based on Kerner's packed-grain model for composite media. Comparisons of theoretical calculations with experimental data show that this model closely approximates the viscoelastic properties of blends with a co-continuous structure, at least in the glass-transition regions of the respective blend components. We have also shown that the storage modulus of co-continuous blends may be well-represented by a discrete-particle model. This result can be misleading, however, if the storage modulus alone is calculated and compared with experimental data. A comparison of viscoelastic data (log E′ and tan δ) with calculation clearly distinguishes the models and indicates that the packed-grain model is the correct representation of the structure of co-continuous blends. The agreement between theory and experiment reported above was principally found in the glass-transition regions of the respective components in the elastomer blend. We extended the comparison well into the rubbery region and found that the agreement between Kerner's mean-field theory and the experimental data was poor, particularly for the loss tangent. Different relaxation mechanisms (relaxations over greater periods of time) are available to the blend in the rubbery region of viscoelastic response, and these mechanisms are apparently not accounted for in the mean-field calculations.

scholarly journals Origin of the emergent fragile-to-strong transition in supercooled water

2018 ◽  
Vol 115 (38) ◽  
pp. 9444-9449 ◽  
Author(s):  
Rui Shi ◽  
John Russo ◽  
Hajime Tanaka
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Supercooled Water ◽  
Arrhenius Law ◽  
Widom Line ◽  
Slowing Down ◽  
Strong Transition ◽  
Dynamical Properties ◽  
Water Models ◽  
Insight Into

Liquids can be broadly classified into two categories, fragile and strong ones, depending on how their dynamical properties change with temperature. The dynamics of a strong liquid obey the Arrhenius law, whereas the fragile one displays a super-Arrhenius law, with a much steeper slowing down upon cooling. Recently, however, it was discovered that many materials such as water, oxides, and metals do not obey this simple classification, apparently exhibiting a fragile-to-strong transition far above Tg. Such a transition is particularly well known for water, and it is now regarded as one of water’s most important anomalies. This phenomenon has been attributed to either an unusual glass transition behavior or the crossing of a Widom line emanating from a liquid–liquid critical point. Here by computer simulations of two popular water models and through analyses of experimental data, we show that the emergent fragile-to-strong transition is actually a crossover between two Arrhenius regimes with different activation energies, which can be naturally explained by a two-state description of the dynamics. Our finding provides insight into the fragile-to-strong transition observed in a wide class of materials.

scholarly journals Thermoelastic Properties of Plain Weave Composites for Multilayer Circuit Board Applications

1999 ◽  
Vol 121 (1) ◽  
pp. 37-43 ◽  
Author(s):  
N. R. Sottos ◽  
J. M. Ockers ◽  
M. Swindeman
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Elastic Moduli ◽  
Mechanical Analysis ◽  
Circuit Board ◽  
Woven Fabric ◽  
Analytical Models ◽  
Thermoelastic Properties ◽  
Lamination Theory ◽  
Thermal Mechanical Analysis

The thermoelastic properties of woven glass/epoxy substrates for multilayer circuit board applications were investigated and the influence of fabric geometry assessed. The woven fabric geometry of several commercially pressed boards was carefully characterized using optical microscopy. The elastic moduli and Poisson’s ratios were then measured in uniaxial tension, while the CTEs of the boards were measured using thermal mechanical analysis (TMA) at temperatures above and below the glass transition. Experimental data were compared to predictions from two new analytical models. One of the models, which does not use classical lamination theory, results in a significant improvement for the prediction of Poisson’s ratio and CTEs. Finally, a parametric study was performed to demonstrate the effect of fiber crimp on the properties of the fabric.

Materials Issues in the Development of High Data-Transfer-Rate Phase-Change Compounds

2001 ◽  
Vol 674 ◽  
Author(s):  
Martijn H.R. Lankhorst ◽  
Herman J. Borg
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Phase Change ◽  
Transfer Rate ◽  
Phase Change Materials ◽  
Data Transfer ◽  
High Data Rate ◽  
Data Transfer Rate ◽  
Glass Transition Temperatures ◽  
High Data

ABSTRACTA model is presented to calculate glass-transition temperatures. This model in combination with experimental data is used to evaluate archival-life stability of common phase change materials Ge2Sb2Te5 and doped eutectic Sb2Te compositions.On the basis of this model, novel high-data-rate phase change compositions have been identified near and on the pseudo-binary line InSb-GaSb in the ternary system Ga-In-Sb.

Effect of Chain Morphology and Carbon-Nanotube Additives on the Glass Transition Temperature of Polyethylene

2013 ◽  
Vol 23 ◽  
pp. 16-23 ◽  
Author(s):  
S. Herasati ◽  
H.H. Ruan ◽  
Liang Chi Zhang
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Glass Transition ◽  
Carbon Nanotube ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Md Simulation ◽  
Md Simulations ◽  
Crystalline Polymers ◽  
Good Agreement

Glass transition temperature Tg is the most important parameter affecting the mechanical properties of amorphous and semi-crystalline polymers. However, the atomistic origin of glass transition is not yet well understood. Using Polyethylene (PE) as an example, this paper investigates the glass transition temperature Tg of PE with the aid of molecular dynamics (MD) simulation. The effects of PE chain branches, crystallinity and carbon-nanotube (CNT) additives on the glass transition temperature are analyzed. The MD simulations render a good agreement with the relevant experimental data of semi-crystalline PE and show the significant effects of crystallinity and addition of CNTs on Tg.

Moisture Sorption Isotherms, Isosteric Heat of Sorption and Glass Transition Temperature of Murtilla (Ugni molinae T.) Berry

2014 ◽  
Vol 10 (4) ◽  
pp. 583-594 ◽  
Author(s):  
Kong S. Ah-Hen ◽  
Roberto Lemus-Mondaca ◽  
Karen A. Mathias-Rettig ◽  
Antonio Vega-Gálvez ◽  
Jessica López
Keyword(s):  
Experimental Data ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Moisture Content ◽  
Sorption Isotherms ◽  
Isosteric Heat ◽  
Sorption Data ◽  
Heat Of Sorption ◽  
Ugni Molinae

Abstract Adsorption and desorption isotherms of fresh and dried murtilla (Ugni molinae Turcz) berries were determined at 20, 40 and 60°C using a gravimetric technique. The experimental data obtained were fitted to eight models, namely GAB, BET, Henderson, Caurie, Smith, Oswin, Halsey and Iglesias–Chirife. A non-linear least square regression analysis was used to evaluate the models. The GAB model best fitted the experimental data. Isosteric heat of sorption was determined from the equilibrium sorption data using the Clausius–Clapeyron equation and was found to decrease exponentially with increasing moisture content. The enthalpy–entropy compensation theory applied to the sorption isotherms indicated an enthalpy controlled sorption process. Glass transition temperature of murtilla was determined by differential scanning calorimetry and modelled as a function of moisture content by the Gordon–Taylor equation and as function of water activity by Roos and Khalloufi models, which proved to be excellent tools for predicting glass transition of murtilla.

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