Fibrous crystallization

Pultz, W. W., and W. Hertl, 1966. Perturbations in the infrared spectra of submicroscopic size, single crystal, fibrous SiC, Spectrochim. Acta, 22, 573-575. 

In practice the structure of any given polymer sample is by no means as regular as the above classification would imply and in most cases defies description in terms of recognizable structural elements. For example, Wunderlich64 shows examples of cobweb structures which can be found in polymers. Clearly, for the purposes of research specific structures have been identified and studied - but this does not mean that a regular solid of macroscopic dimensions may be contracted with these structures. In polymers therefore, we always have to deal with statistical assemblies of elements more or less precisely defined as e.g. lamellar crystal, fibrous crystals, tie chains etc. 

Sylvite (syn., sylvinite) [7447.40-7] [Named after the Dutch chemist and physician of Leyden, Sylvia de la Boe (1614-1672)] (ICSD 22156 and PDF 41-1476) KCl M = 74.551 52.45 wt.%K 47.55 wt.% a (Halides) Coordinence K(6) Cubic fls 629.31 pm Bl,cF8 (2 4) S.G. Fm3m P.G.4-32 Rock salt type Isotropic n = 1.490 2.0 1988 Habit massive, cubic euhedral crystals, fibrous. Color white, yellowish white, reddish white, bluish white, or brownish white. Luster vitreous, greasy. Diaphaneity transparent to translucent. Streak white. Geavage (100), (010), (001). Fracture uneven, brittle, sectile. Soluble in water, the soln. color the flame of a bunsen in violet. Bitter taste. Fusible (m.p. 778°C). 

The SAXS and WAXS patterns of the sample irradiated up to 10 kGy are identical to those of the original sample. The SAXS pattern of the original shows a diffuse scattering in the equatorial direction, but little scattering meridionally and the WAXS patterns show reflection caused by sub-crystals, as well as patterns caused by main crystals (fibrous reflections) as reported by Chatani et al. So only the melting behavior is affected by irradiations below 10 kGy as shown in Fig. 5.1 b. 

Inorganic whiskers, a kind of single crystal fibrous or needle-like material that appeared in recent years, are used to reinforce thermosetting resin, thermoplastic resin, rubber, metal, and ceramics through filling and to prepare advanced engineering plastic, composite materials, adhesive, sealant, and paint. The excellent performances of inorganic whiskers have led to their wide application as composite materials- ... 

The macroscopic orientation of their extended-chain crystals depends on the orientation imparted by flow during mol ding. Because of the fibrous nature of the extended-chain crystals, these materials behave as self-reinforcing composites, with excellent mechanical properties. 

Fibrous Composites. These composites consist of fibers in a matrix. The fibers may be short or discontinuous and randomly arranged continuous filaments arranged parallel to each other in the form of woven rovings (coUections of bundles of continuous filaments) or braided (8). In the case of chopped strand mat the random arrangement is planar. In whisker (needle-shaped crystals or filaments of carbon and ceramics) reinforced materials the arrangement is usually three-dimensional and the resulting composites are macroscopically homogeneous. 

A few months later, a second set of tubes was submitted for examination. These tubes had not been cleaned. Close examination revealed arrowhead-shaped mounds of fibrous debris lodged on the tube wall (Fig. 11.20). Dislodgement of these mounds revealed an arrowheadshaped region of shallow corrosion containing sparkling crystals of cuprous oxide, essentially identical to that described above. 

Disodium 4-nitrophenylphosphate (6H2O) [4264-83-9] M 371.1 Dissolve in hot aqueous MeOH, filter and ppte by adding Me2CO. Wash the solid with Me2CO and repeat the purification. Aq MeOH and Et20 can also be used as solvents. The white fibrous crystals contain less than 1% of free 4-nitrophenol [assay J Biol Chem 167 57 1947]. 

Biological fibers, such as can be formed by DNA and fibrous proteins, may contain crystallites of highly ordered molecules whose structure can in principle be solved to atomic resolution by x-ray crystallography. In practice, however, these crystallites are rarely as ordered as true crystals, and in order to locate individual atoms it is necessary to introduce stereochemical constraints in the x-ray analysis so that the structure can be refined by molecular modeling. 

A characteristic feature of the structure of samples obtained under the conditions of molecular orientation is the presence of folded-chain crystals in addition to ECC. Kawai22 has emphasized that the process of crystallization from the melt under the conditions of molecular orientation can be regarded as a bicomponent crystallization in which, just as in the case of fibrous structures in the crystallization from solutions, the formation of crystals of the packet type (ECC) occurs in the initial stage followed by the crystallization with folding . 

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