Production of Microcellular Polycarbonate Using Carbon Dioxide for Bubble Nucleation

1994 ◽  
Vol 116 (4) ◽  
pp. 413-420 ◽  
Author(s):  
V. Kumar ◽  
J. Weller
Keyword(s):  
Carbon Dioxide ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Bubble Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Homogeneous Microstructure ◽  
Wide Range ◽  
Nucleation Phenomenon

A process to produce a family of novel materials from polycarbonate, having a microcellular structure, is described. The process utilizes the high solubility of carbon dioxide in polycarbonate to nucleate a very large number of bubbles, on the order of 1 to 10 × 109 bubbles/cm3, at temperatures well below the glass transition temperature of the original, unsaturated polycarbonate. Microcellular polycarbonate foams with homogeneous microstructure and a wide range of densities have been produced. In this paper experimental results on solubility, bubble nucleation, and bubble growth in the polycarbonate-carbon dioxide system are presented, and the critical ranges of the key process parameters are established. It is shown that the bubble nucleation phenomenon in polycarbonate near the glass transition temperature is not described by classical nucleation theory.

scholarly journals The Glass Transition Temperature and Temperature Dependence of Activation Energy of Viscous Flow of Ovalbumin

2016 ◽  
Vol 39 (1) ◽  
pp. 13-25
Author(s):  
Karol Monkos
Keyword(s):  
Activation Energy ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Viscous Flow ◽  
Solvent Interactions ◽  
Model Free ◽  
Free Volume Model ◽  
Wide Range ◽  
Different Temperatures

Abstract The paper presents the results of viscosity determinations on aqueous solutions of ovalbumin at a wide range of concentrations and at temperatures ranging from 5°C to 55°C. On the basis of these measurements and three models of viscosity for glass-forming liquids: Avramov’s model, free-volume model and power-law model, the activation energy of viscous flow for solutions and ovalbumin molecules, at different temperatures, was calculated. The obtained results show that activation energy monotonically decreases with increasing temperature both for solutions and ovalbumin molecules. The influence of the energy of translational heat motion, protein-protein and protein-solvent interactions, flexibility and hydrodynamic radius of ovalbumin on the rate of decrease in activation energy with temperature has been discussed. One of the parameters in the Avramov’s equation is the glass transition temperature Tg. It turns out that the Tg of ovalbumin solutions increases with increasing concentration. To obtain the glass transition temperature of the dry ovalbumin, a modified Gordon-Taylor equation is used. Thus determined the glass transition temperature for dry ovalbumin is equal to (231.8 ± 6.1) K.

Analytical Investigation on the Homogeneous Nucleation in a Mono-Component and Bi-Component Droplet

2019 ◽  
Author(s):  
Xi Xi ◽  
Hong Liu ◽  
Chang Cai ◽  
Ming Jia ◽  
Weilong Zhang
Keyword(s):  
Nucleation Rate ◽  
Homogeneous Nucleation ◽  
Ambient Pressure ◽  
Analytical Investigation ◽  
Bubble Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Liquid Temperature ◽  
Wide Range ◽  
Good Agreement

Abstract The work attempts to analyze the performance of homogeneous nucleation by using the non-equilibrium thermodynamics theory and the classical nucleation theory. A nucleation rate graph was constructed under a wide range of operating temperature conditions. The results indicate that the superheat limit temperature (SLT) estimated by the modified homogeneous nucleation sub-model is in good agreement with the experimental results. The nucleation rate increases exponentially with the liquid temperature rise when the liquid temperature exceeds the SLT under atmospheric pressure. The superheated temperature needed to trigger the bubble nucleation decreases with the elevated ambient pressure.

scholarly journals Predicting the influence of particle size on the glass transition temperature and viscosity of secondary organic material

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Markus Petters ◽  
Sabin Kasparoglu
Keyword(s):  
Particle Size ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Melting Point ◽  
Critical Role ◽  
Particle Diameter ◽  
Cloud Formation ◽  
Melting Point Depression ◽  
Wide Range

Abstract Atmospheric aerosols can assume liquid, amorphous semi-solid or glassy, and crystalline phase states. Particle phase state plays a critical role in understanding and predicting aerosol impacts on human health, visibility, cloud formation, and climate. Melting point depression increases with decreasing particle diameter and is predicted by the Gibbs–Thompson relationship. This work reviews existing data on the melting point depression to constrain a simple parameterization of the process. The parameter $$\xi $$ ξ describes the degree to which particle size lowers the melting point and is found to vary between 300 and 1800 K nm for a wide range of particle compositions. The parameterization is used together with existing frameworks for modeling the temperature and RH dependence of viscosity to predict the influence of particle size on the glass transition temperature and viscosity of secondary organic aerosol formed from the oxidation of $$\alpha $$ α -pinene. Literature data are broadly consistent with the predictions. The model predicts a sharp decrease in viscosity for particles less than 100 nm in diameter. It is computationally efficient and suitable for inclusion in models to evaluate the potential influence of the phase change on atmospheric processes. New experimental data of the size-dependence of particle viscosity for atmospheric aerosol mimics are needed to thoroughly validate the predictions.

Miscibility, Isothermal Crystallization/Melting Behavior and Morphology of Poly(Trimethylene Terephthalate)/Poly(Buthylene Terephthalate) Blends

2008 ◽  
Vol 54 ◽  
pp. 243-248 ◽  
Author(s):  
Pongpipat Krutphun ◽  
Pitt Supaphol
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Amorphous State ◽  
Minor Component ◽  
The Body ◽  
Nucleation Theory ◽  
Melting Point Depression ◽  
Melt Crystallization ◽  
Trimethylene Terephthalate

Blends of poly(trimethylene terephthalate) (PTT) and poly(buthylene terephthalate) (PBT) in the amorphous state were miscible in all of the blend compositioins studied, as evidenced by a single, composition-dependent glass-transition temperature observed for each blend composition. The variation in the glass-transition temperature was well-predicted by the Gordon- Taylor equation, with the fitting parameter being 1.37. The cold-crystallization (peak) temperature increased with increasing PBT content in the blends. The subsequent melting endotherms after melt crystallization exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of minor component of the blends. LHW and NLHW were used to determine the equilibrium melting temperature of the blends. The values of the overall crystallization rate parameters for these blends were all found to increase with decreasing crystallization temperature, suggesting that these blends crystallized at low temperatures faster than that at high temperatures. As the content of PBT was further increased, these values dramatically decreased. This result is similar to that observed in the growth rate. From LH secondary nucleation theory, PTT ,PBT and their blends showed the transition temperatures between regime III and II about 194oC. Banded spherulites were observed for PTT/PBT blends. The spacing of bands of PTT increases with increasing Tc. The body of spherulite texture is more open with increasing PBT content. In addition, the boundary of spherulite is also changed with composition.

A study on the progress of mutarotation above and below the Tg and the relationship between constant rates and structural relaxation times

2017 ◽  
Vol 19 (31) ◽  
pp. 20949-20958 ◽  
Author(s):  
K. Wolnica ◽  
M. Dulski ◽  
E. Kaminska ◽  
A. Cecotka ◽  
M. Tarnacka ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Structural Relaxation ◽  
Relaxation Times ◽  
Ftir Studies ◽  
Wide Range ◽  
The Relationship

Comprehensive FTIR studies on the progress of mutarotation in d-fructose mixed with maltitol have been carried out over a wide range of temperatures, both above and below the glass transition temperature Tg.

Free Volumes in Polymer Nanocomposites

2008 ◽  
Vol 607 ◽  
pp. 177-179 ◽  
Author(s):  
Hong Min Chen ◽  
L. James Lee ◽  
Jin Tao Yang ◽  
Xiao Hong Gu ◽  
Yan Ching Jean
Keyword(s):  
Carbon Dioxide ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Positron Annihilation ◽  
Polymer Nanocomposites ◽  
Carbon Nanofiber ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Combination Effect ◽  
Positron Annihilation Lifetime

We have employed positron annihilation lifetime spectroscopy to measure the free volumes in nanocomposites of polystyrene with addition of carbon nanofiber (CNF) and carbon dioxide as a function of composition and of temperature. We found that the glass transition temperature (Tg) increases as a function of CNF compositions but significantly decreases as the exposure of CO2. We also investigate the combination effect of CNF and CO2 and found that the CO2 significantly weakens the bonding between PS and CNF interfaces. The Tg changes are compared with DSC.

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