Refractive index values

Dispersion forces, the so-called London forces 5, are the highest when solute and solvent electrons are polarized. These forces are high when the refractive index values are high. Solvents with high refractive indexes will dissolve solutes with high refractive indexes. 

II Look at the refractive index values given in Fig. 2.4m and then see if you can answer the questions below. 

The advantages of SPR experiments are that only small amounts of sample are required,72 often hundreds of microliters of solutions with nanomolar to micromolar concentration of reactants and the substrate attached to the surface can oftentimes be reused after washing in buffer. The fact that changes in the refractive index values are measured avoids the need to use absorption or fluorescence markers to follow the binding kinetics. 

In both cases, the incident angle is monitored using a goniometer or a CCD and converted to effective refractive index values using the above equations. 

Using the refractive index value of the pyrazine LB film, we calculated the mode dispersion curves of the TM fundamental and the TM second-harmonic waves in the waveguide device composed of a waveguiding pyrazine layer and a fused quartz substrate when Nd YAG laser is used as a fundamental light (Fig. 18). These curves show that the Cerenkov type phase matching is possible in the range of the thickness from 410 nm to 510 nm. 

An instrument known as a refractometer has been used for many years to measure the refractive index of liquids and liquid solutions for the purpose of both quantitative and qualitative analysis (see Chapter 15). A refractometer measures the degree of refraction (or bending) of a light beam passing through a thin film of the liquid. This refraction occurs when the speed of light in the sample is different from a reference liquid or air. The refractometer measures the position of the light beam relative to the reference and is calibrated directly in refractive index values. It is rare for any two liquids to have the same refractive index, and thus this instrument has been used successfully for qualitative analyses. 

The type of measurements that are needed to accomplish the task should also be considered. Refractive index values are generally needed for measurements based on light scattering. Densities are often needed for techniques based on acoustics and sedimentation. Further, most approaches require the samples to be dissolved or suspended in a liquid. Thus, information related to how the liquid affects particle shape and association is also important. 

Refractive index values vary from 1.0003 for air to over 2.7 for some solid oxide ceramics. Silicate glasses have a much narrower range of valnes, from abont 1.5 to 1.9. The refractive indices (or indexes) of other materials can be fonnd in Appendix 9. 

Above the critical intrinsic viscosity of 1.1 dPg, both refractive index values remained relatively constant. Thus, the UNB initially increased with increasing intrinsic viscosity and then reached a maximum above the critical intrinsic viscosity. Lowering the molecular weight may disrupt the packing owing to... 

Optically uniaxial crystals may be tetragonal, hexagonal, or trigonal. If it is possible to recognize a shape characteristic of a particular system this information is useful supplementary evidence but it must be emphasized that the refractive index values by themselves are usually sufficient for identification. 

Some of the latest work on high refractive index polyphosphazenes makes use of polymers that contain both fluoroalkoxy and di- or tri-chlorophenoxy side groups.261 These amorphous glasses are thermally stable up to 400 °C, show a large variation of refractive index with temperature, and refractive index values that vary from 1.39-1.56 depending on composition. Thus, they are candidates for uses in thermo-optical switching devices. 

For optically uniaxial crystals we know that the refractive index values for extraordinary waves are variable, with that for ordinary waves fixed. We can link this observation with that concerning the vibration directions for the two waves travelling along a general wave normal direction the ordinary vibration direction is always perpendicular to the optic axis, while the extraordinary vibration is always in the plane containing the optic axis and wave normal direction. This suggests that we may connect the variation of the refractive index in the crystal with the vibration direction of the light. This concept allows a convenient representation of anisotropic optical properties in the form of a spatial plot of the variation of refractive index as a function of vibration direction. Such a surface is known as the optical indicatrix. 

Compute the refractive index values from the relationship between i/q, (i, and A. 

The refractive index of a transparent substance is the ratio of the velocity of light in air to its velocity in that material under like conditions. It is equal to the ratio of the sine of the angle of incidence made by a ray in air to the sine of the angle of refraction made by the ray in the material being tested. The refractive index values specified in this Codex are for the D line of sodium (589 nm) unless otherwise specified. The determination should be made at the temperature specified in the individual monograph, or at 25° if no temperature is specified. This physical constant is used as a means for identification of, and detection of impurities in, volatile oils and other liquid substances. The Abbe refractometer, or other refractometers of equal or greater accuracy, may be employed at the discretion of the operator. 

Pawluk-Kolc, M., Zi ba-Palus, J., Zadora, G. Differentiation of glass fragments on the basis of refractive index values determined by the theimoimmersion method. Application in criminalistics. Probl. Forensic Sci. 56, 48-64 (2003)... 

The control of the deposition thickness is crucially important in the LCVD operation, regardless of the modes of operation. However, it is very difficult to measure the actual thickness of ultrathin film deposited on polymeric substrates. If an LCVD film is deposited on polymeric substrates, such as films, fibers, and molded articles, it is nearly impossible to determine the thickness by a simple nondestructive method that can be done quickly enough to monitor the LCVD operation. In order to circumvent this problem, the use of special substrates added or attached to the normal substrate is found to be satisfactory. A small piece of Si wafer is a typical case of this approach. Ellipsometer can measure the deposition on the Si wafer easily and quickly, which provides thickness and refractive index values. 

The Onsager equation is the one most used for H bonded systems. For solutions, the experimentally determined dielectric constant is commonly plotted in terms of polarization (see Table 2-1) against concentration. Extrapolation to infinite dilution gives and hence the dipole moment. The last steps require knowledge of the electronic (Pe) and atomic (P ) polarizations. The value of Pe is usually found from refractive index values, and Pa (fortunately small) is estimated or... 

The refractive index values of solid oxides lie in the range of 1.3 to 2.7 with silicate glasses they vary between 1.5 and 1.9, while extreme values exhibited by special glasses are 1.35 and 2.25. The Abbe value lies in the range of 20 to 100. Current soda-Iime--silica and borosilicate glasses have 1.48 — 1.53 and v = 58 —70. The refractive index is increased most by PbO and BaO. The dispersion usually increases simultaneously with refractive index. 

Here, ve is the main electronic absorption frequency in the UV, typically around 3xl015s-1 [6], An analysis of the above equation shows some interesting consequences. A close match between the dielectric constants of the interacting bodies leads to diminishing values of the first term. The second term (determined by the refractive index values) shall then play the dominant role in the surface forces in this case. This effect can be utilized in force spectroscopy to maximize pull-off forces. On the other hand, interaction forces can also be minimized by a proper choice of the medium. Both these aspects will be important later for AFM-based force spectroscopy. 

The overall tendency of compounds to interact through dispersion forces is related to the refractive index values of the compounds (see Karger et al., 1973) the greater the refractive index the stronger the dispersion interactions. Thus, the dipolar aprotic solvents and pyridine have the strongest influences in dispersion interactions of the compounds listed in Table 1. Where refractive index is used to measure the concentration of solute it is, of course, important to maximize the differences in these values between solute and solvent. 

The refractive index values measured under "standard" conditions (with the most commonly used wavelengths of light, at room temperature) will be correlated directly with the -type connectivity indices. 

Equations (92) and (93) show that the presence of a solvent medium other than a free space much reduces the magnitude of van der Waals interactions. In addition, the interaction between two dissimilar molecules can be attractive or repulsive depending on refractive index values. Repulsive van der Waals interactions occur when n3 is intermediate between nx and n2, in Equation (92). However, the interaction between identical molecules in a solvent is always attractive due to the square factor in Equation (93). Another important result is that the smaller the n - nj) difference, the smaller the attraction will be between two molecules (1) in solvent (3) that is the solute molecules will prefer to separate out in the solvent phase which corresponds to the well-known like dissolves like rule. However there are some important exceptions to the above explanation, such as the immiscibility of alkane hydrocarbons in water. Alkanes have nx = 1.30-1.36 up to 5 carbon atoms, and water has a refractive index of n = 1.33, and very high solubility may be expected from Equation (93) since the van der Waals attraction of two alkane molecules in water is very small. Nevertheless, when two alkane molecules approach each other in water, their entropy increases significantly because of the very high difference in their dielectric constants and also the zero-adsorption frequency contribution consequently alkane molecules associate in water (or vice versa). This behavior is not adequately understood. 

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