Semi-crystalline structure

Early on, before the existence of macromolecules had been recognized, the presence of highly crystalline structures had been suspected. Such structures were discovered when undercooling or when stretching cellulose and natural rubber. Later, it was found that a crystalline order also existed in synthetic macromolecular materials such as polyamides, polyethylenes, and polyvinyls. Because of the polymolecularity of macromolecular materials, a 100% degree of crystallization cannot be achieved. Hence, these polymers are referred to as semi-crystalline. It is common to assume that the semi-crystalline structures are formed by small regions of alignment or crystallites connected by random or amorphous polymer molecules. 

The semi-crystalline structures often formed by crystallizable polymers are known to consist of thin crystalline lamellae separated by amorphous regions [1-3]. For crystallization from the melt, where the conditions are far from equilibrium, the polymer chains must achieve a regular conformation from the highly entangled melt and align parallel to each other to form thin... 

Plastic deformation of the original semi-crystalline structure... 

For PEMFCs, the solid electrolytes are polymer membranes polymers modified to include ions, usually sulfonic groups. One of the most widely used membranes today is the polymer Nafion , created by the DuPont company. These membranes have aliphatic perfluorinated backbones with ether-linked side chains ending in sulfonate cation exchange groups [6, 7], Nafion is a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether [8] and has a semi-crystalline structure [9], This structure (which resembles Teflon ) gives Nafion long-term stability in oxidative or reductive conditions. The sulfonic groups of the polymers facilitate the transport of protons. The polymers consist of hydrophilic and hydrophobic domains that allow the transport of protons from the anode to the cathode [10, 11],... 

The water molecule has an approximately tetrahedral charge distribution, two positive charges at the positions of the hydrogen atoms (/ HOH = io41/2°) and two negative induced charges. The semi-crystalline structure of water and also the crystal structures of the modifications of ice show a similarity to... 

Conducting polymers such as polyacetylene, polypyrrole, polyaniline, polythiophene, etc. have been actively studied for use in various fields due to their interesting properties batteries,46 electrochromic displays,47 materials for supercapacitors,48 corrosion protection,49 protecting layers for static electricity,50 materials for organic electroluminescence displays,51 sensing materials,52 etc. Polypyrrole is reported to be extremely rigid, with a semi-crystalline structure. 

FIGURE 40.1 Fringed-micelle model of a linear polymer with semi-crystalline structure. 

At a molecular level, the development of the neck means that the stress apphed to the fiber is apparently rather high therefore it leads to the break up of the semi-crystalline structure with random orientation of the crystallites (i.e. the one shown in Figure 4.1 c). In the neck zone the structure rearranges since polymer chains align on stretching. As a result, the chains are eventually orientated as shown in Figure 4.3 a. So the fiber becomes anisotropic and therefore stronger. 

Starch occurs as discrete granules whose size and shape depends on its botanical origin. However, all stareh granules have a semi-crystalline structure, hydrated only to a very small extent, insoluble in cold water, and very dense. 

The complex deformation behaviour of ETFE-foils depends substantially on their morphological structure. The semi-crystalline structure is characterised by entanglement and flexibility of the molecular chains. The whole deformation behaviour of ETFE-foils under exposure can be separated into... 

Due to the presence of MDI and highest molecular weight, the material PUOX2 showed a good viscosity value (0.62 dl/g). The PUOXi 4 series (especially the DBDI materials) and polymer PUDB displayed a semi-crystalline structure. The crystallinity degree varied from 5.49% (PUOX3) to 18.84% (PUOX4). 

Block copolymers, as we shall see later, are able to phase separate and it is possible for one of these phases to have semi-crystalline structure. Whether or not a crystalline phase is observed depends on the relative molar masses of the elements that form the polymer chain and their ability to pack into the required... 

XRD patterns of PEO/PVP blend films (Figure 19.1) showed peaks at around 19.2°, 22.5°, 23.6°, 25.5°, 26.2°, 27.1°, 29.7°, 32.6°, 36.6° and 39.6° and are attributed to the crystalline phase of PEO. These peaks appear to superimpose on a broad hump between 18 and 50 which could be due to the amorphous nature of PEO. A broad peak at around 13° is associated with the amorphous nature of PVP The intensity of all crystalline peaks decreases gradually in all XRD patterns with salt concentration suggesting a decrease in the degree of crystallinity of the complex. This could be due to the disruption of the semi crystalline structure of the films by salt. No sharp peaks correspond to NaF salt were observed in all PEO/PVP complexes, indicating the complete dissolution of salt in the polymer matrix. 

For plastics with a subsequent semi-crystalline structure, e.g., HOPE in Figure 3.4b, the plastic should set under constant pressure (isobaric procedure) down to the crystallisation temperature T. Release of the heat of crystallisation causes a retardation of the temperature drop, while at the same time there is a rapid fall in specific volume. There is a partial arrangement of molecules into ordered structures called crystallites. 

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