Birefringent organics

Figure 3. Percentage of birefringent organics compared with peat types in two cores from the Okefenokee Swamp.

Figure 4. Percentage of birefringent organics in each of 3 samples of peat from Minnesota, Maine, North Carolina, and Georgia.

Noncrystalline domains in fibers are not stmctureless, but the stmctural organization of the polymer chains or chain segments is difficult to evaluate, just as it is difficult to evaluate the stmcture of Hquids. No direct methods are available, but various combinations of physicochemical methods such as x-ray diffraction, birefringence, density, mechanical response, and thermal behavior, have been used to deduce physical quantities that can be used to describe the stmcture of the noncrystalline domains. Among these quantities are the amorphous orientation function and the amorphous density, which can be related to some of the important physical properties of fibers. 

Many ceUulosic derivatives form anisotropic, ie, Hquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety of solvents (56,57). The nature of the polymer—solvent interaction determines the concentration at which hquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birefringent polymer solution. Strong organic acids, eg, trifluoroacetic acid are most effective and can produce an anisotropic phase with concentrations as low as 28% (58). Trifluoroacetic acid has been studied with cellulose triacetate alone or in combination with other solvents (59—64) concentrations of 30—42% (wt vol) triacetate were common. 

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

To this list of protein misfolding diseases can be added rare familial amyloidoses in which the mutated proteins have the classic amyloid fibril congophilic birefringence and cross-(3-sheet structure (Table 3). Many of these deposits have an impact on the central nervous system (TTR, cystatin, lysozyme) as well as on other organ systems. A newly described disease, familial British dementia, is associated with the deposition of Abri, a 34 amino acid, 4 kDa peptide cleaved from a 277 amino acid precursor sequence, the last 10 amino acids of which are not normally translated [52]. Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is... 

Deterioration of rubbers, fibres or plastics resulting from attack by living organisms. Birefringence... 

Birefringence (or double refraction) is the decomposition of a light ray into two rays when it passes through certain types of crystalline material. This occurs only when the material is anisotropic, that is, the material has different characteristics in different directions. Amylose and amylopectin polymers are organized into a radially anisotropic, semicrystalline unit in the starch granule. This radial anisotropy is responsible for the distinctive... 

Nitration of chitin was carried out for the first time by Fiirth and Scholl [54J. They tried to produce degradation of the chitin by acting with fuming nitric acid (d 1.525). They obtained two products one insoluble in the common organic solvents, the other soluble in polar solvents. Most likely they were nitrochitin and the oxidation product, respectively. The authors pointed out a similarity between nitrochitin and nitrocellulose. Later on, Schmidt [55] examined the birefringence of chitin and nitrochitin. 

For a typical chiral organic compound, such as 2-butanol, the circular birefringence, nL - wR, at A = 589 nm is of the order of 10-7. Even for a very high a = 40° mm-1 at A = 589 nm ( wL - nR 2 X 10 4), linear birefringence, which may arise from residual ordering/aggregation of polymer chains, could easily overwhelm the circular birefringence. 

A convincing demonstration of the anisotropic organization of these hybrid xerogels is their birefringence when observed in polarized light. This analysis is usually performed on liquid crystal compounds in order to determine their mesoscopic anisotropic organization. 

Microscopic examination of these samples show for the PET-rich blends the presence of very small spherulites. The PBT-rich blends show very low birefringence, low turbidity, and no organized structures. The SALS patterns are circularly symmetrical. 

Microscopic examination of the samples crystallized at 130°C shows very low turbidity and birefringence for the PBT samples the turbidity in the blends increased, and small spherulites were present for PET. The samples crystallized at 110°C again showed small spherulites for PET, and no organized structures were observed in the blends of intermediate composition although their turbidity was quite high with samples of very high PBT composition, the turbidity was lost. 

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