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The most basic model for polymer crystallization kinetics comes from Hoffman nucleation theory. The crystallization process of polymers does not always obey simple chemical rate equations. Polymers can crystallize through a variety of different regimes and unlike simple molecules, the polymer crystal lamellae have two very different surfaces.
The percent crystalline content of a polymer can be estimated from the crystallization/melting peaks of the DSC graph using reference heats of fusion found in the literature. [25] DSC can also be used to study thermal degradation of polymers using an approach such as Oxidative Onset Temperature/Time (OOT); however, the user risks contamination ...
Polymers have both a melting temperature T m and a glass transition temperature T g. Above the T m, the polymer chains lose their molecular ordering and exhibit reptation, or mobility. Below the T m, but still above the T g, the polymer chains lose some of their long-range mobility and can form either crystalline or amorphous regions. In this ...
When above the melting temperature but below the clearing point, the thermotropic LCPs will form liquid crystals. Above the clearing point, the melt will be isotropic and clear again. Frozen liquid crystals can be obtained by quenching liquid crystal polymers below the glass transition temperature.
At temperatures between −8 °C (18 °F) and 8 °C (46 °F), the aging process is enhanced drastically. Amylose crystallization occurs much faster than crystallization of the amylopectin. The crystal melting temperature of amylose is much higher (about 150 °C (302 °F)) than amylopectin (about 50–60 °C (122–140 °F)).
By melting and solidifying at the phase-change temperature (PCT), a PCM is capable of storing and releasing large amounts of energy compared to sensible heat storage. Heat is absorbed or released when the material changes from solid to liquid and vice versa or when the internal structure of the material changes; PCMs are accordingly referred to ...
The crystals are captured, stored, and sputter-coated with platinum at cryo-temperatures for imaging. The crystallization process appears to violate the second principle of thermodynamics. Whereas most processes that yield more orderly results are achieved by applying heat, crystals usually form at lower temperatures – especially by ...
Some polymer solutions also have a lower critical solution temperature (LCST) or lower bound to a temperature range of partial miscibility. As shown in the diagram, for polymer solutions the LCST is higher than the UCST, so that there is a temperature interval of complete miscibility, with partial miscibility at both higher and lower temperatures.