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Drawn semi-crystalline polymers are the strongest polymeric materials due to the stress-induced ordering of the molecular chains. [27] Other defects, such as voids, occur in the semi-crystalline polymer under tensile stress and can drive the formation of the neck. The voids can be observed via small angle x-ray scattering.
In polymer physics, spherulites (from Greek sphaira = ball and lithos = stone) are spherical semicrystalline regions inside non-branched linear polymers. Their formation is associated with crystallization of polymers from the melt and is controlled by several parameters such as the number of nucleation sites, structure of the polymer molecules, cooling rate, etc. Depending on those parameters ...
All polymers (amorphous or semi-crystalline) go through glass transitions. The glass-transition temperature ( T g ) is a crucial physical parameter for polymer manufacturing, processing, and use. Below T g , molecular motions are frozen and polymers are brittle and glassy.
Strain crystallization occurs when the chains of molecules in a material become ordered during deformation activities in some polymers and elastomers. [2] The three primary factors that affect strain crystallization are the molecular structure of the polymer or elastomer, the temperature, and the deformation being applied to the material. [3]
Amorphous materials, such as liquids and glasses, represent an intermediate case, having order over short distances (a few atomic or molecular spacings) but not over longer distances. Many materials, such as glass-ceramics and some polymers , can be prepared in such a way as to produce a mixture of crystalline and amorphous regions.
In the case of polymers, conformational changes of segments, typically consisting of 10–20 main-chain atoms, become infinitely slow below the glass transition temperature. In a partially crystalline polymer the glass transition occurs only in the amorphous parts of the material. The definition is different from that in ref. [9]
Polyamorphism is also an important area in pharmaceutical science. The amorphous form of a drug typically has much better aqueous solubility (compared to the analogous crystalline form) but the actual local structure in an amorphous pharmaceutical can be different, depending on the method used to form the amorphous phase.
Amorphous materials have an internal structure of molecular-scale structural blocks that can be similar to the basic structural units in the crystalline phase of the same compound. [4] Unlike in crystalline materials, however, no long-range regularity exists: amorphous materials cannot be described by the repetition of a finite unit cell.