Birefringence determination

Pennell (1987) discussed the differences between alite birefringences determined with thin sections (the present author s data) and powder mounts, illustrating the fact that the latter determination was not accurate, but concluding that the values may be tolerable for correlation purposes. 

Alite birefringence determined in thin section, using quartz as an internal thickness standard, is a suitable method. However, a correlation with burning temperature was not evident. 

In response to Fundal (1982), Lee (1983) pointed out the bimodality of alite birefringence determined by Maki and Kato (1982), who demonstrated relationships with magnesium oxide content in the crystal. Lee restated the conclusion by Maki and Kato that the M, (monoclinic) phase appears pseudotrigonal in an X-ray powder-diffraction pattern. Lee believed that Fundal s comparison of alite compositional and optical data with a tectosilicate solid-solution series, such as plagio... 

Table 2. Observed refractive indices of para-aromatic polyamide fibers and a PBO fiber, radially lateral, n, tangentially lateral, Hji lateral, n longitudinal. The results of Weeda were obtained by matching immersion liquids under the interference microscope, or from measuring the retardation [139]. For PBO fiber ii was estimated from a birefringence determination...

In this equation, the saturation electric field governs the electric behavior of blue phase LC, while saturated induced birefringence determines the optical behavior and thus the wavelength dispersion of blue phase. It still follows the normal dispersion trend and agrees very well with the single-band model. 

The superstructure of hard elastic polypropylene (HEPP) fibre was investigated, By means of SAXS studies, stress in various media, and birefringence determinations, a more precise model is suggested. 

Let us consider investigation of stresses in a 3-D specimen. It has been shown [1] that in the case of weak birefringence a 3-D specimen can be investigated in a conventional transmission polariscope as if it were a two dimensional specimen. On every ray of light it is possible to determine the parameter of the isoclinic and the optical path difference A. The latter are related to the components of the stress tensor on the ray by linear integral relationships... 

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 direction of orientation in HDPE film and the orientation degree can be determined by either the x-ray method, ir polarization spectroscopy, acoustical methods, or birefringence (21,22,120,121). 

Optical Properties. When light falls on an object, it is either partially absorbed, reflected, or transmitted. The behavior of the object as it relates to each of these three possibiUties determines visual appearance. Optical properties of fibers give useful information about the fiber stmcture refractive indexes correlate well with fiber crystalline and molecular orientation and birefringence gives a measure of the degree of anisotropy of the fiber. 

Optical properties of fibers are measured by light microscopy methods. ASTM D276 describes the procedure for fiber identification using refractive indexes and birefringence. Other methods for determining fiber optical properties have been discussed (3,38—44). However, different methods of determining optical properties may give different results (42). 

With polarizers fidly crossed and the specimen rotated to maximum brightness, the sample thickness is determined with the aid of a calibrated eyepiece micrometer, and the polarization (retardation) color is noted. From these the birefringence may be determined mathematically or graphically with the aid of a Michel-L vy chart. 

The quantitative assessment of the overall orientation of PET fibers is generally made on the basis of fiber optical anisotropy measurements, i.e., measurements of the optical birefringence of the fiber. The determination of the value of optical birefringence makes it possible to determine the value of Hermans function of orientation based on the equation ... 

Lagorceix, H., Reynaud, R, 1995, Squeezing highly Birefringent Fiber for an Accurate Nondestructive Determination of Principal-Axis Orientation along the Waveguide application to Fiber Babinet Compensator Implementations Optical Fiber Technology 1, 171... 

Birefringence allows the determination of the second moment of the ODF with respect to a given axis as ... 

The uniaxial orientation parameter related to the orientation of polymer chains gains particular importance, because it can also be determined by measurement of birefringence [250,252],... 

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