Fringe micelle, structures

Semi-crystalline random 1. fringed micelle structure... 

Figure 7. Fringed micelle structure of polymers and orientation effects on bulk...

Crystalline polymers appear to be the most studied by ESR techniques. The model wiiich seems to emerge from these results is, in fact, a variant of a model proposed over twenty years ago by Cumberbirch and associates (Shirley Institute Memoirs) to explain the tenacity of wet raycm monofilaments. Briefly, Cumberbirch, et al propose a fringe-micelle structure in which the fringe r ons, swollen by water, are assumed to obey rubber elasticity theory. These fringe reglcms are, of course, the more accessble (to water), more disordered, r ons of the semicrystalline structure. 

Figure 10.83). Some attention has also been given to lamellar [267] and folded-chain structures [268]. Examination of rayon by the electron microscope has provided ample evidence for fibrillar structure in rayon. Although the fringed fibril structure shown in Figure 10.83 appears to fit best with the tendency of some rayons to fibrillate in the wet state under certain conditions the fringed micelle structure can also account for observed properties. 

Wellinghoff ST, Shaw J, Baer E (1979) Polymeric materials from the gel state. The development of fringed micelle structure in a glass. Macromolecules 12 932... 

Direct electron microscopic evidence for basic particles in a polymerising system is scarce, but they have been identified in equilibrium with primary particle nuclei (41). However Behrens (42) reported that the smallest particles resolvable by electron microscopy in a grain produced by suspension polymerisation were lOnm diameter. This view has been supported by Barclay (43) and more recently by Soni et al (44) who concluded that each basic particle was composed of a crystalline core surrounded by less ordered material in a likely fringed micelle structure. 

Crystalline polymers do not completely crystalUze, but there is a tendency to form grains similar to metals. This structure is known as the fringed micelle structure and is shown in Figure 1.12. l thin the grains there is the regular aystaUine phase. Between the grains there is the amorphous phase. 

FIGURE 1.12 Fringed-Micelle structure of crystalline polymers. 

The fringed micelle theory has been less favoured recently following research on the subject of polymer single crystals. This work has led to the suggestion that polymer crystallisation takes place by single molecules folding themselves at intervals of about 10 nm to form lamellae as shown in Figure 3.3b. These lamellae appear to be the fundamental structures of crystalline polymers. 

If the ordered, crystalline regions are cross sections of bundles of chains and the chains go from one bundle to the next (although not necessarily in the same plane), this is the older fringe-micelle model. If the emerging chains repeatedly fold buck and reenter the same bundle in this or a different plane, this is the folded-chain model. In either case the mechanical deformation behavior of such complex structures is varied and difficult to unravel unambiguously on a molecular or microscopic scale. In many respects the behavior of crystalline polymers is like that of two-ph ise systems as predicted by the fringed-micelle- model illustrated in Figure 7, in which there is a distinct crystalline phase embedded in an amorphous phase (134). 

The traditional model used to explain the properties of the (partly) crystalline polymers is the "fringed micelle model" of Hermann et al. (1930). While the coexistence of small crystallites and amorphous regions in this model is assumed to be such that polymer chains are perfectly ordered over distances corresponding to the dimensions of the crystallites, the same polymer chains include also disordered segments belonging to the amorphous regions, which lead to a composite single-phase structure (Fig. 2.10). 

In the present concept of the structure of crystalline polymers there is only room for the fringed micelle model when polymers of low crystallinity are concerned. For polymers of intermediate degrees of crystallinity, a structure involving "paracrystals" and discrete amorphous regions seems probable. For highly crystalline polymers there is no experimental evidence whatsoever of the existence of discrete amorphous regions. Here the fringed micelle model has to be rejected, whereas the paracrystallinity model is acceptable. 

It is now generally accepted that the morphology of a polymer depends on the contributions of three different macro-conformations (a) the random coil or irregularly folded molecule as found in the glassy state, (b) the folded chain, as found in lamellar structures and (c) the extended chain. The fringed micelle (d) may be seen as mixture of (a), (b) and (c) (see Fig. 2.12) with paracrystallinity as an extreme. 

By contrast, total molecular architecture, involving the conjunction of crystalline and amorphous parts, has proved to be much less amenable to investigation. For a long time structural interpretations were based on the fringed-micelle model in which molecules are supposed to wander through... 

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