Fibrous birefringence

Fibers of tourmalines up to 8 inches long have been described from the Alps (Dietrich et al., 1966). Novad and Zak (1970) described shorter and thinner (diameter < 1 micrometer) tourmaline fibers from the Ural mountains. With high birefringence and pleochroism, tourmaline is readily identified by optical examination. It is distinguished from other fibrous silicates... 

The optical character of chalcedony is distinct from that expected for the normally uniaxial mineral, quartz, and signals the fibrous nature of a particular sample. The direction of fiber elongation is often parallel to the [1120] crystallographic direction of the quartz structure (Fig. 2.19A), but other fiber directions have also been determined within a single sample (Frondel, 1985). The presence of helically twisted fibers are suspected from the variations in extinction and birefringence noted along the fiber length (Fig. 2.19C). More detailed information on the optical or other physical and chemical properties of quartz and its many varieties can be found in volume 3 of Palache et al. (1962) and in Frondel (1985). 

In contrast to the fibrous and well-oriented polysaccharides (such as cellulose and chitin), amylose in its natural state is found only in more-or-less spherical starch granules. Amylose is the minor constituent of most starches, and is a linear polymer of a-D-(l—>4)-linked D-glucose residues. The birefringence of starch grains was already well known at the turn of the century, and the cross of isocline pattern between crossed Nicols was interpreted in terms of radially arranged crystallites. Later,... 

Triacetate, fibrous material, mp 226 -227. Can be formed into strong films which can be elongated 550%. Becomes birefringent and does not develop crystallinity. 

Amyloid deposits are fibrous protein structures of high P-sheet content that are identified microscopically from their staining characteristics, giving a green birefringence when stained with the dye Congo red. 

Cassim et al., 1968 empirical Specific birefringence of various fibrous proteins in vitro 1.7 X 10 2 ... 

Determination of molecular symmetry. Molecular symmetry of P. can be determined from measurements of viscosity, streaming birefringence, rates of sedimentation and diffusion, or directly by electron microscopy, For a known M, the frictional coefficient can be calcnlated from ultracentrifugal measurements, e.g. from the sedimentation /= [Mfl - vp)]/S, where v is the partial specific volume, p is the density and S is the sedimentation constant. The axial ratio a/b of a P. can be derived from the frictional ratiowhereis the/of a spherical molecule. The value of a/b for most globular P. is between 2 and 20, and greater than 20 for fibrous R, e, g. the axial ratio of fibrinogen is 30. 

At 90 days, the sutures were becoming translucent and had lost some of their birefringent properties. A few of the suture cross-sections stained pink (eosinophilic) around the periphery and the edges w ere indistinct, indicating the onset of absorption. The tissue reactions generally consisted of a fibrous capsule and a layer of macrophages interposed between it and the suture surface. 

The theory of cold-drawing of synthetic fibres has been reviewed together with the mechanical, general physical, and thermal characteristics of polyester fibres. Drawing, fibrous structure, and fibrillation,and the influence of orientation on crystallinity and birefringence have also been studied and a model proposed for orientational strengthening in 2GT. ... 

The fiber diameter distribution was studied by microscopy (optical microscope, Hitachi TM-1000 scanning electron microscope). Fiber orientation was studied by using birefringence and polarization IR-spectroscopy (SPECORD M 80 IR-spectrometer). Crystalline phase of polymer was studied by differential scaiming calorimetry (DSC) (differential scanning calorimeter). The packing density of fibrous materials was calculated as a function of airflow resistance variation with a special manometric pressure unit [7]. 

Examination of fibrous materials by electron microscopy showed that the fibrous material uncovered by the current-conducting layer decomposes in 1-2 min, when exposed by electron beam. Examination of polymer orientation in fibers by using birefringence showed that elementary fibers in non-woven fabric are well oriented along fiber direction. However, it is impossible to determine the degree of orientation quantitatively because the fibers are packed randomly. 

Extensive studies on the optical anisotropy of hydrated cellulosic gel in relation to deformation have been reported by Kratky " and by Hermanns. "" Kratky studied the deformation mechanism of fibrous materials by means of X-ray diffraction and birefringence, and postulated two kinds of deformation models for the swollen gel, in order to explain the orientation mechanism of the structural units in terms of the orientation distribution (but not in terms of the average degree of orientation of the structural units). Hermanns carried out studies on the same lines as Kratky, and introduced one of the orientation factors as a measure of the average degree of orientation. ... 

Some of the generalized orientation factors defined by equations (15) and (16) have been independently reported by several authors. One of the second order orientation factors F200 has been proposed by Hermanns and Platzek to relate the birefringence of fibrous materials to the uniaxial orientation of cylindrical-symmetric structural units, and F q has been defined by Stein and Norris to characterize the uniaxial orientation of polyethylene crystals. F220 F 2 Iso the... 

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