Morphology microfibrils

We suggest that both the lamellar and the microfibrillar morphologies are formed by a nucleation and growth process. A low nucleation density of crystal solvates results in a lamellar morphology, whereas a high nucleation density of the crystalline PBT results in formation of microfibrils. 

The same authors 369,3701 also obtained similar results if the liquid crystal solvent was aligned by flow during the polymerization. They showed that the polymerization conditions lead to alignment of the fibrils within the polymer mass and of the chains within the fibrils polymers produced in this way could also be doped to a conductivity of 104 S cm-1 371). The morphology of polyacetylene produced by polymerization in a liquid crystal solvent, aligned both magnetically and by flow, has been studied by Montaner et al. 371). They show that the polymer film is made up of very long fibrils built from microfibrils. In one fibril, the orientation of microcrystalline domains with respect to the fibril axis is very well defined, whilst the orientation of the different fibrils in the sample spreads over 20°. 

Sherratt, M. J., Holmes, D. F., Shuttleworth, C. A., and Kielty, C. M. (2004). Substrate dependent morphology of supra-molecular assemblies Fibrillin and type VI collagen microfibrils. Biophys. J. 86, 3211-3222. 

A new type of composite material starting from polymer blends has been developed. Due to the fact that the reinforcing elements are the basic morphological entities of oriented polymers, the microfibrils, these new composites have been named microfibrillar-reinforced composites (MFC) (Evstatiev Fakirov, 1992). MFC, however, clearly differ from traditional composite systems. Since the microfibrils are not available as a separate component, the classical approach to composite preparation is inappropriate for MFC mannfactnring. 

The fact that both the neat components and their blends are relatively well characterized with respect to their varying structures and morphologies as a result of the applied mechanical and thermal treatments, permits us to follow the gradual variation of microhardness as a function of structural parameters. In this way one can obtain the H values for material components which are not accessible to direct experimental determination. Furthermore, having the extrapolated values for completely amorphous and fully crystalline homopolymers and starting from a knowledge of the number of components (and/or phases) one can make use of the additivity law (eq. (1.5)) to evaluate the mechanical properties of components which cannot be isolated or do not exist as individual materials. A good example of this are the PET microfibrils studied here (Fig. 5.16(b)). 

Extended chain crystals have been implicitly included in the treatment on lattice visualization of crystallized homopolymers. While crystals obtained by crystallization under extension may be imperfect compared to the classical examples of high-pressure crystallization [61], these examples are closer to many applications. The morphology of fibrils and microfibrils of PTFE has been analyzed by CM-AFM (Fig. 3.14). A second example discussed below refers to cold-drawn PET (Fig. 3.17), which is crystallized in extended chain crystals. 

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