Refractive indices, defined determination

Other terms relating to physical properties include viscosity refractive index pour point, ie, the lowest temperature at which the oil flows flash point, ie, the temperature at which the oil ignites and aniline point, ie, the minimum temperature at which equal volumes of oil and aniline are completely miscible. These are determined under defined conditions estabHshed by ASTM. 

If measurements are made in thin oxide films (of thickness less than 5 nm), at highly polished Al, within a small acceptance angle (a < 5°), well-defined additional maxima and minima in excitation (PL) and emission (PL and EL) spectra appear.322 This structure has been explained as a result of interference between monochromatic electromagnetic waves passing directly through the oxide film and EM waves reflected from the Al surface. In a series of papers,318-320 this effect has been explored as a means for precise determination of anodic oxide film thickness (or growth rate), refractive index, porosity, mean range of electron avalanches, transport numbers, etc. 

The MOLWT-II program calculates the molecular weight of species in retention volume v(M(v)), where v is one of 256 equivalent volumes defined by a convenient data acquisition time which spans elution of the sample. I oment of the molecular weight distribution (e.g., Mz. Mw. Mn ) are calculated from summation across the chromatogram. Along with injected mass and chromatographic data, such as the flow rate and LALLS instruments constants, one needs to supply a value for the optical constant K (Equation la), and second virial coefficient Ag (Equation 1). The value of K was calculated for each of the samples after determination of the specific refractive index increment (dn/dc) for the sample in the appropriate solvent. Values of Ag were derived from off-line (static) determinations of Mw. 

Salinity measurements are most often used in oceanography to determine seawater density. The conventional measure used by oceanographers for determining salinity is conductivity. This is feasible because the salt content of seawater is well defined, as is the temperature-related compressibility. As an alternative, the refractive index of water is a good descriptor of density when temperature is known or can be measured. Refractive index provides a high-precision method for determining the density of pure water. As various salts are added, the refractive index is a less exact predictor of density, although relative measurements can still be useful. 

The application of refractive index and differential viscometer detection in SEC has been discussed by a number of authors [66-68]. Lew et al. presented the quantitative analysis of polyolefins by high-temperature SEC and dual refractive index-viscosity detection [69]. They applied a systematic approach for multidetector operation, assessed the effect of branching on the SEC calibration curve, and used a signal averaging procedure to better define intrinsic viscosity as a function of retention volume. The combination of SEC with refractive index, UV, and viscosity detectors was used to determine molar mass and functionality of polytetrahydrofuran simultaneously [70]. Long chain branching in EPDM copolymers by SEC-viscometry was analyzed by Chiantore et al. [71]. 

Colorimetric resonant reflection Si3N4 [31] 3.4 X 10 An (determined by solvents with defined refractive index) 0.4 pg/ mm dried BSA 0.1-1.0 ng/mL streptavidin to immobilized biotin... 

The ellipsometric parameters xl> and A experimentally determined with a homogeneous thick sample, are algebraically related with the components of the dielectric function, which in turn define the refractive index and the absorption index (Bom and Wolf, 1980). The parameters for the strong oscillator used to simulate the spectra shown in Fig. 6.4-5 were chosen to resemble the strong infrared resonance of quartz glass. Radiation reflected from such a sample was measured ellipsometrically the evaluation led to the results presented In Fig. 6.4-14. For weaker absorbers such as many molecular compounds. 

The density of a liquid is defined as the weight of the liquid per unit volume (usually one milliliter). It is one of the more easily determined properties, and it is necessary for the calculation of molar refraction. Before simple refractometers became available, the density was considered a particularly important datum for characterizing liquids, but its use has now been largely superseded by the refractive index. However, it still remains a useful physical property. 

Solvent polarity is very difficult to define, but essentially refers to the solvation power of a solvent. Quantitative determination of solvent polarity is equally difficult, and quantitative methods rely on physical properties such as dielectric constant, dipole moment, and refractive index. It is not possible to determine the solvent polarity by measuring an individual solvent property due to the complexity of solute-solvent interactions and for this reason empirical scales of solvent polarity, based on chemical properties, are most widely used. The principal properties used to estimate solvent polarity are summarized in Table 2 and the most important of these methods are embellished below. 

Here V is the molal volume of the liquid, N is Avagadro s number, K the. Boltzmann constant, T the absolute temperature, and is the angle between the vectors jj, and Ji. ag is the polarizability of the molecules in the liquid it can be determined from the refractive index. For highly polar substances is small compared to the second term in the parenthesis. The high dielectric constant of water is well accounted for by equation (47) on the basis of the known dipole moment of water, and the orientation of the water molecules relative to one another. The molar polarization of the liquid is defined in terms of the polarizability and the dipole moment of the molecules by equation (47). In a solution containing several components equation (47) becomes... 

The above discussion reveals how NR can be used to provide direct information concerning both the thickness and the composition via the SLD of the various layers in the interface. This constitutes an advantage over ellipsometry or surface plasmon resonance methods where the value of the refractive index (composition) of the film is usually assumed in order to determine its thickness. However, to use the kinematic approach to directly determine these quantities, the reflectivity has to be measured in a sufficiently large range of so that at least one-half of the longest period interference fringe, corresponding to the thirmest layer in the interface, is observed on the reflectivity curve. The spatial resolution for a film of thickness ris defined as t= 7r/Qz,max, where is the maximum momentum... 

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