INDEX measurement with

Optical properties also provide useful stmcture information about the fiber. The orientation of the molecular chains of a fiber can be estimated from differences in the refractive indexes measured with the optical microscope, using light polarized in the parallel and perpendicular directions relative to the fiber axis (46,47). The difference of the principal refractive indexes is called the birefringence, which is illustrated with typical fiber examples as foUows. Birefringence is used to monitor the orientation of nylon filament in melt spinning (48). 

Water Content and Refractive Index. The water content of a hydrophilic contact lens is a determinant of other properties. The relationship of water content and Dk is discussed above. Water content in lenses is inversely related to refractive index (23), a key property for vision correction. A lens material with a higher refractive index refracts light to a greater degree, allowing more vision correction with a thinner material. The water content of a lens is generally determined gravimetricaHy or inferred from the relationship to refractive index, measured with a refractometer (24). 

Figure 4. Comparison of the phase diagrams determined from the refractive index measurements with that obtained by the visual method. The weight fraction w is the concentration variable. Empty symbols are used, when the compositions are estimated from refractive index data (Cemim+BFJ in 1-butanol (A), 1-pentanol (y), 2-butanol (0), and 2-pentanol (<)), full symbols, when the data are obtained by the visual method observing the separation temperature in samples of different composition (Gemini+ in water ( ), 1-propanol (O). 1-butanol (A), 2-butanol (y), 1-pentanol (0), 2-pentanol (<), and 1-hexanol (>)).

It is usually best to measure the refractive index of the solutions to which protein has not been added and then make a small correction of dilution. However, in cases where the protein concentration is low, it is acceptable to make the refractive index measurement with that solution.)... 

By an assortment of thermodynamic manipulations, the quantities dn/dp and [N (d G/dp )o] can be eliminated from Eq. (10.48) and replaced by the measurable quantities a, /3, and dn/dT the coefficients of thermal expansion, isothermal compressibility, and the temperature coefficient of refractive index, respectively. With these substitutions, Eq. (10.48) becomes... 

Solution Polymers. Acryflc solution polymers are usually characterized by their composition, solids content, viscosity, molecular weight, glass-transition temperature, and solvent. The compositions of acryflc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—liquid chromatography, and refractive index measurements (97,158). The solids content of acryflc polymers is determined by dilution followed by solvent evaporation to constant weight. Viscosities are most conveniently determined with a Brookfield viscometer, molecular weight by intrinsic viscosity (158), and glass-transition temperature by calorimetry. 

Antimony Oxide. The effect of antimony trioxide on the oxygen index of flexible poly(vinyl chloride) containing from 20 to 50 parts of plasticizer is shown in Figure 2. The flame resistance as measured by the oxygen index increases with the addition of antimony oxide until the oxygen index appears to reach a maximum at about 8 parts of Sb202. Further addition of antimony oxide does not have any increased beneficial effect. 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

The width of molecular weight distribution (MWD) is usually represented by the ratio of the weight—average and the number—average molecular weights, MJM. In iadustry, MWD is often represented by the value of the melt flow ratio (MER), which is calculated as a ratio of two melt indexes measured at two melt pressures that differ by a factor of 10. Most commodity-grade LLDPE resias have a narrow MWD, with the MJM ratios of 2.5—4.5 and MER values in the 20—35 range. However, LLDPE resias produced with chromium oxide-based catalysts have a broad MWD, with M.Jof 10—35 and MER of 80-200. 

The color of TSR L is measured with a Lovibond Comparator using methods outlined in the relevant International Standard (16). Raw mbber is molded into a disk 1.6 mm thick, and the color is compared and matched with that of standard glass disks. These glass disks provide a color index scale in which the higher index values correspond to darker colors. Generally the specification for TSR L is a maximum Lovibond individual value of 6 and range... 

The refractive index of a film or a substrate material can be measured with a sensitivity better than 5 x 10, the best available for non-invasive optical measurement methods, especially for thin films. The extinction coefficient can be measured with almost the same sensitivity, which corresponds to a lower limit of 10-100 cm for the absorption coefficient of the material. 

The refractive index of a medium is the ratio of the speed of light in a vacuum to its speed in the medium, and is the square root of the relative permittivity of the medium at that frequency. When measured with visible light, the refractive index is related to the electronic polarizability of the medium. Solvents with high refractive indexes, such as aromatic solvents, should be capable of strong dispersion interactions. Unlike the other measures described here, the refractive index is a property of the pure liquid without the perturbation generated by the addition of a probe species. 

The distance of each reflection from the center of the pattern is a function of the fiber-to-film distance, as well as the unit-cell dimensions. Therefore, by measuring the positions of the reflections, it is possible to determine the unit-cell dimensions and, subsequently, index (or assign Miller indices to) all the reflections. Their intensities are measured with a microdensitometer or digitized with a scanner and then processed.8-10 After applying appropriate geometrical corrections for Lorentz and polarization effects, the observed structure amplitudes are computed. This experimental X-ray data set is crucial for the determination and refinement of molecular and packing models, and also for the adjudication of alternatives. 

Most suitable for the examination of the surface is x-ray photoelectron spectroscopy, whereas the wettability determination can be established by a detailed interpretation of core flooding experiments and wettability index measurements. The results of such studies show that the organic carbon content in the surface is well correlated with the wetting behavior of the material characterized by petrophysical measurements [1467,1468]. 

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