Refractive index and polarization

Solvents with different polarities and refractive indexes significantly affect carotenoid optical properties. Because the refractive index is proportional to the ability of a solvent molecule to interact with the electric held of the solute, it can dramatically affect the excited state energy and hence the absorption maxima positions (Bayliss, 1950). Figure 7.2a shows three absorption spectra of the same xanthophyll, lutein, dissolved in isopropanol, pyridine, and carbon disulfide. The solvent refractive indexes in this case were 1.38, 1.42, and 1.63 for the three mentioned solvents, respectively. 

Table 4.3 Solvent polarity and refractive index of tested vapors46,47...

For the evaluation of the response of the sensor, we selected several vapors of different polarity. The vapors included water (H20), acetonitrile (ACN), toluene, and dichloromethane (DCM). Solvent polarity and refractive index of tested vapors are listed in Table 4.346 47. The spectral range for the evaluation of the vapor responses of the colloidal crystal film was selected as 700 995 nm, which covered only the fundamental Bragg diffraction peak on the (111) planes of the colloidal crystal film to further reduce effects from possible stacking defects in the film as suggested in the literature44. 

In the early 1970s, Earth-based measurements of the polarization and refractive index of the cloud particles led to their identification as droplets of concentrated (—75% by mass) sulfuric acid (Esposito et al., 1983). Several years later. Barker (1979) discovered SO2 at Venus cloud tops. Almost simultaneously, instmments on the Pioneer Venus and Venera 11-12 missions also observed SO2. 

The real utility of d comes in the analysis of thin films. Consider a substrate of refractive index supporting a thin film of thickness d and refractive index in contact with an internal reflection element (the prism) of refractive index as shown in Figure 24. In this case, d depends on the polarization of the incident light beam and is given by... 

The dielectric constant and refractive index parameters and different functions of them that describe the reactive field of solvent [45] are insufficient to characterize the solute-solvent interactions. For this reason, some empirical scales of solvent polarity based on either kinetic or spectroscopic measurements have been introduced [46,47]. The solvatochromic classification of solvents is based on spectroscopic measurements. The solvatochromic parameters refer to the properties of a molecule when its nearest neighbors are identical with itself, and they are average values for a number of select solutes and somewhat independent of solute identity. 

According to the mode of parameter correlation, Ej(30) was introduced in the group of parameters that describe the acidity of solvent and partially its polarity, and n in the group of parameters that present the dielectric properties of solvents. Quantitative relations between different parameters of polarity, such as correlation between the n scale or and the dielectric constant and refractive index of... 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Quantitative determination of solvent polarity is 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... 

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

We notice that as particle size increases the Rayleigh minimum fades smoothly into the overall structure of the surface. Comparison of Figure 12 with Figure 8 suggests that the main effect of polarization is the superposition of the Rayleigh minimum on a regular pattern determined by size and refractive index. 

An analysis of the t(30) values, using multivariate statistical methods, has been carried out by Chastrette et al. [193]. According to this analysis, the x(30) values of non-HBD solvents are measures of the dipolarity and polarizability as well as the cohesion of the solvents. Another analysis of x(30) values in terms of functions of the dielectric constant sf and refractive index ( d) of forty non-HBD solvents has been given by Bekarek et al he emphasizes the predominant influence of the f(fir) term on the iix(30) parameter of those solvents [194]. For further correlations of the x(30) values with other empirical parameters of solvent polarity, see Section 7.6. 

In the intrinsic sensors, generally a tapered, fased-silica fiber is used, on which and after decladding of the core, specific biological receptors are immobilized via a well-establish chemical procedure. Changes in the absorbance, luminescence, polarization or refractive index are detected. But direct measmement is not usually possible and competitive configurations are employed using fluorescent labels (see Fig. 5.4b). 

BekSrek and coworkers40 related the effect of the medium on the spectrum of 2-nitroaniline to the relative permittivity and refractive index of the solvents. In subsequent work, BekSrek and coworkers52 53 employed several probes, including 5, 8, 9, 10 and 15 as well as some that have not been mentioned previously 3-nitro-AAAAdimethylaniline (46), 4-nitroso-A ,A -dimethy I aniline (47) and Af-(2-nitrophenyl)piperidine (48), as probes to explore the polarity/polarizability and HBA/EPD properties of a large number of polar and non-polar aprotic aliphatic solvents. The wavenumbers could be fitted to expressions similar to equations 10 and 11, but with a cross-term of the permittivity and refractive index included (equation 12) ... 

Koppel-Palm solvent parameters Parameters to measure separately the ability of a solvent to enter into nonspecific solvent-solute interactions (permittivity, , and refractive index, nD) and specific solvent-solute interaction (solvent basicity or NUCLEOPHILICITY B and solvent acidity or ELECTROPHILICITY E) as contributing to overall solvent POLARITY. 

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