An overview of the nonequilibrium behavior of polymer glasses

Tant, Martin R.; Wilkes, Garth L.

doi:10.1002/pen.760211403

Cited by 214 publications

(93 citation statements)

References 56 publications

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“…The results of this study are considered important due to the widespread use of this material. Results of a similar study on block copolymers will be reported elsewhere (13,14).…”

Section: Introductico-mentioning

confidence: 96%

Physical aging studies of semicrystalline poly(ethylene terephthalate)

Tant

Wilkes

1981

J of Applied Polymer Sci

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Physical aging of semicrystalline poly(ethylene terephthalate) has been investigated as a function of crystalline content. Stress–strain, stress relaxation, and differential scanning calorimetry experiments were used to monitor the physical aging process. Both the overall extent and the rate of physical aging in this material decrease with increasing crystallinity. Several possible reasons for this behavior are advanced and discussed. It was also found that the drawing behavior of amorphous PET changes significantly as physical aging progresses. Specifically, for samples aged and then elongated, the extent of localized deformation (necking) and associated strain‐induced crystallization was greater for samples aged for longer periods of time.

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“…The results of this study are considered important due to the widespread use of this material. Results of a similar study on block copolymers will be reported elsewhere (13,14).…”

Section: Introductico-mentioning

confidence: 96%

Physical aging studies of semicrystalline poly(ethylene terephthalate)

Tant

Wilkes

1981

J of Applied Polymer Sci

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“…The kinetic stability of glasses is of fundamental importance when studying the effects of time and externa1 conditions (temperature, pressure, and humidity) on glassy behaviors (Moynihan et al, 1976;Tant and Wilkes, 1981;Berens and Hodge, 1982;Eisenberg, 1984;Jewell and Shelby, 1990;Levine, 1991,1994;Angell et al, 1994;Franks, 1994). The concept of kinetic stability originates from the way a glass is formed and can be explained using cryopreservation principles.…”

mentioning

confidence: 99%

“…Because of the high viscosity, the glass system is inhibited from rapidly reaching its equilibrium state. Nevertheless, there is still a "driving force" for the glass to achieve equilibrium (Tant and Wilkes, 1981;Franks, 1994). For that reason, the glass is described as kinetically stable but not thermodynamically stable.…”

mentioning

confidence: 99%

A Calorimetric Study of the Glass Transition Behaviors in Axes of Bean Seeds with Relevance to Storage Stability

Leprince

Walters

1995

Plant Physiol.

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Although the presence of intracellular aqueous glasses has been established in seeds, their physiological role in storage stability is s t i l l conjectural. Therefore, we examined, using differential scanning calorimetry, the thermal behavior of glass transitions in axes of bean (Phaseolus vulgaris 1.) with water contents (WC) between O and 1 g H,O/g dry weight (g/g) and temperatures between -120 and +120°C. Three types of thermal behaviors associated with the glass transition were observed. The appearance, the glass + liquid transition temperature, and the amount of energy released during these transitions were dependent on the tissue WC. No glass transitions were observed at WC lower than 0.03 and higher than 0.45 g/g. A brief exposure to 100°C altered the glass properties of tissues with WC between 0.03 and 0.08 g/g but did not affect the thermal behavior of glasses with higher WC, demonstrating that thermal history is important t o the intracellular glass behavior at lower WC. Correspondence of data from bean to models predicting the effects of glass components on the glass --z liquid transition temperature suggests that the intracellular glasses are composed of a highly complex sugar matrix, in which sugar and water molecules interact together and influence the glass properties. Our data provide evidente that additional glass properties must be characterized to understand the implications of a glassy state in storage stability of seeds.Water and temperature play a significant and fundamental role in determining the storage longevity of orthodox seeds. Early models developed from storage experiments suggested that water and temperature were independent variables (Justice and Bass, 1978; Roberts and Ellis, 1989). However, theoretical considerations (Vertucci, 1992;Vertucci and Roos, 1993) and experimental data (Vertucci and Roos, 1993;Vertucci et al., 1994aVertucci et al., , 1994b have demonstrated that the effects of water and temperature on seed aging are interdependent. Conceptual models have been introduced to describe the interdependencies of WC and temperature on seed longevity. They rely on the findings that the nature and kinetics of degradative reactions in seeds change according to the physical properties of water

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“…7) This includes increase in density, yield stress, and modulus and decrease in creep and stress relaxation rate. 8) Aging procedure is also known to increase the brittleness and lower the impact strength of glasses.…”

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confidence: 99%

Effect of Structural Relaxation on the Physical and Aerosol Properties of Amorphous Form of FK888 (NK1 Antagonist)

Tanaka

Kitamura

Kitagawa

2005

CHEMICAL & PHARMACEUTICAL BULLETIN

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The use of amorphous form of drug substances to improve solubility, accelerate dissolution, and promote therapeutic activity has been very important for the development for water insoluble solids as pharmaceutical dosage forms. 1)However, not only chemical degradation 2) but also physical change such as crystallization 3,4) and aggregation 5,6) of amorphous solids even below their glass transition temperature (Tg) were reported, and these instabilities of most amorphous solids preclude their more widespread use in pharmaceutical dosage forms. Such advantages and disadvantages are offered due to excess properties of amorphous systems in terms of enthalpy and free energy. These high energy systems are unstable and tend to spontaneously revert back to the thermodynamically stable state. Thus, amorphous solids may crystallize, or even if crystallization does not occur on pharmaceutical shelf life, amorphous solids will 'relax' toward the equilibrium supercooled liquid state as shown in Fig. 1. As a glass moves towards the equilibrium state, energy decreases, free volume decreases, and structural order increases, i.e., configurational entropy decreases. Thus, this process is called structural relaxation. As the intact amorphous state indicated in Fig. 1 is of higher enthalpy than the equilibrium state, heat is given off during the relaxation process, and this process is known as enthalpy relaxation. This process has strong temperature dependence, and the relaxation rate is maximal close to the Tg while negligible relaxation occurs at temperatures far below it. This means that relaxation of the amorphous materials would occur during pharmaceutical unit operations involving thermal or mechanical stresses. For glassy polymers, time dependent changes in physical and mechanical properties are often attributed to relaxation.7) This includes increase in density, yield stress, and modulus and decrease in creep and stress relaxation rate.8) Aging procedure is also known to increase the brittleness and lower the impact strength of glasses. 9)Thus, there is a large possibility that aging should affect the physical properties of amorphous solids, and those studies in pharmaceutical systems have focused on the measurement of relaxation times in relation to the stability prediction based on their molecular mobility. 10,11) Despite that amorphous drug substances can take various enthalpy states, there are few studies 12) to investigate its effect on their properties. FK888 (NK1 antagonist) is a candidate drug for migraine, and is developed as dry powder inhalers (DPIs) to avoid the first-pass effect and minimize unwanted side effects. The solid state of FK888 drug substance is adopted to be amorphous considering its low solubility in aqueous solution, and it is confirmed that the amorphous state is obtained constantly in industrial scale size. In the dosage form of DPIs, because the respirable fraction of the emitted dose is largely dependent on the geometric size of bulk drug particles, not * To whom correspondence should be addre...

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An overview of the nonequilibrium behavior of polymer glasses

Cited by 214 publications

References 56 publications

Physical aging studies of semicrystalline poly(ethylene terephthalate)

Physical aging studies of semicrystalline poly(ethylene terephthalate)

A Calorimetric Study of the Glass Transition Behaviors in Axes of Bean Seeds with Relevance to Storage Stability

Effect of Structural Relaxation on the Physical and Aerosol Properties of Amorphous Form of FK888 (NK1 Antagonist)

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