Micelles fringed model

Fringed micelle model Frings acetator Frisium Frit... 

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). 

Figure 8 Fringe-micelle model of crystalline polymers. (PramRef. 131,)...

It has been suggested that glass transition is an important physicochemical event that controls the phase transition process of starch (Biliaderis, 1998). According to Biliaderis (1998), the "fringe-micelle" model (Fig. 5.16) does not permit assignment of a definite Tg for most starches. This is because the change in heat capacity during phase... 

Fig. 7. Schematic representation of the fringed micelle model of crastalline polymers... 

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). 

The fringed micelle model gives an extremely simple interpretation of the "degree of crystallinity" in terms of fractions of well-defined crystalline and amorphous regions. Many excellent correlations have evolved from this model through the years, so that it has long been popular. 

A second important event was the development by Hosemann (1950) of a theory by which the X-ray patterns are explained in a completely different way, namely, in terms of statistical disorder. In this concept, the paracrystallinity model (Fig. 2.11), the so-called amorphous regions appear to be the same as small defect sites. A randomised amorphous phase is not required to explain polymer behaviour. Several phenomena, such as creep, recrystallisation and fracture, are better explained by motions of dislocations (as in solid state physics) than by the traditional fringed micelle model. 

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. 

Frequently used combinations of groups, 141 Fresnel s relationship, 297 Friction, 840 coefficient, 831 Fringed micelle model, 29 Fugacity, 756 coefficient, 756... 

Whatever the cause of this small amount of crystalline phase, the dimensions of a crystallite (ca. 100 A) are much smaller than a chain length, and it is likely that a given chain will go through two or more crystallites, which will then be connected by one or more covalent links. This situation is similar to the one known in polymer physics as the fringed micelle model (see Ref. 12, p. 187), and is sketched on Fig. 9. This has consequences on the behavior of films upon stretching (see Section II.D.3). 

If the fringed micelle model (see Section II.C.5.a) is applicable, large values of, which would correspond to distances between crystallites greater than the length of the chain connecting them, imply breaking of covalent bonds this may place the limit for fracture of the sample. 

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... 

FIGURE 8-51 Schematic diagram depicting the fringed micelle model. 

Flgure 2.1 Conformational differences of polymer chains in the amorphous and crystalline states. Fringed micelle model. Parallel and coiled lines represent, respectively, portions of chains in the crystalline and the amorphous regions. 

While the fringe-micelle model for crystalline polymers has not been fashionable for some time, it may have some utility in modeling stress transfer and faUure mechanisms. In any event, a fringe micelle model is a primitive form of more general composites models which attempt to model the behavior of crystalliiM polymers using the same techniques as for filled S5rstems or fiber reinforced plastics. The ESR studies may serve to provide valuable insight into the validity of such models for... 

Figure 6 The fringed micelle model of polymer microstructure...

Figure 2.17 Schematic representation of (a) fofd plane showing regular" chain folding, (b) ideal stacking of lamellar crystals, (c) interlamellar amorphous model, and (d) fringed micelle model of randomly distributed crystallites.

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