glass transition


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Glass transition

The transition that occurs when a liquid is cooled to an amorphous or glassy solid. This can occur only if the cooling rate is fast enough to prevent crystallization which would otherwise occur if time had been sufficient for the sample to reach true equilibrium at each temperature. Since the crystal is invariably the thermodynamically stable low-temperature phase, the glass transition corresponds to a transition from a high-temperature liquid into a nonequilibrium meta-stable low-temperature solid. See Amorphous solid, Crystal, Viscosity

For many organic and polymeric systems, the difficulty of molecular packing and the steric hindrances are sufficient to prevent crystallization, and glass formation in these systems is relatively easy. In other systems, for example, metallic systems, rapid quench rates on the order of 106 K/s (2 × 106 °F/s) may be necessary to avoid crystallization, suggesting that any system can be quenched from the liquid state to an amorphous glassy state assuming that the system can be cooled rapidly enough.

glass transition

[′glas tran‚zish·ən]
(physics)
The transition that occurs when a liquid is cooled to an amorphous or glassy solid.
(physical chemistry)
The change in an amorphous region of a partially crystalline polymer from a viscous or rubbery condition to a hard and relatively brittle one; usually brought about by changing the temperature. Also known as gamma transition; glassy transition.
References in periodicals archive ?
These linkages serve to increase flexibility and reduce the glass transition temperature.
This rapid change in modulus is associated with a very important phenomenon that all polymers exhibit, called the glass transition. This transition is a relaxation that involves the amorphous portion of the material.
As a model case, they focused on glass transition temperature, an index of heat resistance.
KUWAIT, Aug 27 (KUNA) -- The Kuwait Institute for Scientific Research (KISR) has registered an unprecedented patent for measurement of glass transition temperatures of polymers.
With its high glass transition temperature and high crystallinity, the mechanical performance and the heat-aging performance of ForTii Ace are superior to rival polyphthalamides based on polyamides 6T, 9T and 10T.
The ink composition includes a mono-functional monomer having a glass transition point of -30[degrees]C or lower, and a polyfunctional monomer having a glass transition point of 0[degrees]C or lower.
They cover density, thermal properties, and the glass transition temperature of glasses; infrared spectroscopy; Raman spectroscopy; Brillouin light scattering; neutron diffraction techniques for structural studies; X-ray diffraction from glass; X-ray absorption fine structure (SAFS) spectroscopy and glass structure; nuclear magnetic resonance spectroscopy; advanced dipolar solid-state nuclear magnetic resonance spectroscopy; and atom probe tomography.
More specifically, chemists and physicists have struggled to describe key aspects of the glass transition, such as the concept of molecular "cages" that form as the temperature drops and the surface begins to harden.
However their low thermal stability (low glass transition temperature) or their tendency to crystallize prevent their use in OLED products.
In a certain temperature range, this change reaches the maximum, the storage modulus decreases rapidly, and this temperature range is the glass transition region.
The thermal expansion was obtained over a range of 30[degrees] to 210[degrees]C, while the glass transition temperature ([T.sub.g]) was determined by the differential thermogravimetric analysis (Setaram instrumentation Labsys DTA/6) at heating rate of 20 K [min.sup.-1].
Chemists and physicists who specialize in glass present a range of modern theoretical and experimental views of the glass transition and relaxations in glassy systems, phenomena that have perplexed scientists, artisans, and artists since ancient times.