Lamellar structure, growth

There is no adequate theory for lamellar growth of Ni(P). Periodic fluctuations in the content of phosphorus in electroless Ni(P) are possible causes of the lamellar structure. 

The fiberlike crystalline structures (shish) are highly stable to the point that they can be superheated [31]. Therefore, it is believed that the core of the shish is formed by crystallization of completely stretched polymer chains. The kebabs are believed to be folded-chain lamellar structures. The direction of growth of the kebabs is normal to the shish. The chain ahgnment in the kebabs is believed to be parallel to the shish. Similar structures are obtained by crystalhzation in polymer melt films exposed to orientational deformation [32,33]. These two-dimensional shish-kebabs also consist of a central fiber, shish, and periodically attached linear kebabs, with growth direction normal to the shish. 

The process of development of a mosaic texture was observed by Taylor (2) first in thermally metamorphosed coals and then in partially carbonized vitrinite. He noted the appearance of spherical bodies in the plastic vitrinite, their growth, and the final development of the mosaic texture which is characteristic of the walls of the vesicular coke structure. From their appearance and behavior in polarized light it was deduced that the spherical bodies probably had a single plane of preferred orientation—i.e., a lamellar structure. 

Fig. 2.4. The often dramatic effects bottom contacts can have on molecular ordering in organic semiconductors like pentacene. A. Schematic diagram of the type of disorder introduced in pentacene s lamellar structure as thin-film growth encounters a step, for example...

In addition to the one-dimensional templated structure of the MCM-41 materials, two- and three-dimensional systems have also been prepared. A number of papers have used the lamellar structures of amphiphile assemblies to prepare flat, striated metal oxide materials [72,73]. These materials often exhibit enhanced properties over materials that have uncontrolled three-dimensional growth. Vesicles have also been used to engineer spherical imprints into silicates [74,75]. Even more elaborate supramolecular surfactant systems, that yield toroidal and other unusually shaped metal oxides, have also been reported [76,77]. 

All the aspects and processes discussed above apply also to the crystallisation of polymers [18-31]. However, in addition, the connectivity of the monomers causes several restrictions. One of the most obvious ones is represented by the quasi-two-dimensional lamellar shape of polymer crystals. A lamella is formed by crystalline segments of the chain (the stems) arranged vertically and limited (on top and below) by amorphous (fold) surfaces. Therefore, polymer crystals grow essentially only in two dimensions. Growth in the third dimension is rather difficult, in particular when the polymer contains non-crystallisable units which will segregate to the surfaces of the crystals. Growth in the third dimension necessitates deviations from the perfect lamellar structure, e.g. screw dislocations. The topic of polymer crystallisation has been the subject of a tremendous amount of studies over the last 60 years [5-8,10-65],... 

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