Temperature Dependence of Refractive Index

The temperature dependence of the refractive index has been evaluated with the empirical Eykman equation  

Riddick, J. A., Organic Solvents Physical Properties and Methods of Purification, 4th ed., 1986. New York Wiley. 

Nelken, L. H., Index of Refraction, in Handbook of Chemical Property Estimation, W. J. Lyman, W. F. Reehl, and D. H. Rosenblatt, Editors, 1990. Washington, DC American Chemical Society, p. 26. 

The Merck Index An Encyclopedia of Chemicals, Drugs, and Biologicals, 11th ed., 1989. Rahway, NJ Merck Co., Inc. 

Molecular Connectivity in Chemistry and Drug Research, 1976. San Diego, CA Academic Press. 

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Variation of refractive index of the MNA solution in various solvents at 20 C as a function of concentration was obtained using an Abbe refractometer. Refractive indices available,as shown in Figure 5, range from 1.4 to 1.5 with the solvents used, from which one can easily match the refractive index of silica optical fibers. Temperature dependence of refractive index in MNA saturated solutions,measured at 15 C and 250C,is tabulated in Table 2. Fluctuation of refractive index,as a result of the temperature variation, turned out to be approximately 0.0004/ 0, so that It is essential to control the solution temperature to better than 0.1 in this experiment,in order for only electronic nonlinear refractive index change to be effective. 

The most common type of universal detector by far is the differential refractive index (DRI) detector. (Here, the word universal denotes the ability to respond to all chemical functionalities.) It senses differences in refractive index between a moving (sample containing) stream and a static reference of mobile phase using a split optical cell. It responds well (at a moderate concentration level) to most polymeric samples, provided that they are different in refractive index from the mobile phase in which they are dissolved. Despite the temperature independence of the SEC separation phenomenon, the DRI is highly temperature sensitive as a result of the strong temperature dependence of refractive index. 

FIGURE 7.2 Dependence of refractive index of Teflon AF on glass transition temperature. (Fromhttp //www2.dupont.com/Teflon industrial/en US/), DuPont, 2008. With permission.)... 

The index of refraction of chalcogenide glasses is considerably higher than of oxide glasses, and therefore, it is usually necessary to coat the optical elements with antireflecting coatings (Hilton (1966)). The temperature dependence of the index of refraction was studied by Hilton and Jones (1967). 

The glass transition temperature in thin polymer films or nanometric polymer layers can be deduced from ellipsometric measurements by determining the kink in the temperature dependence of the index of refraction n and the layer thickness d. Calculating the second derivative with respect to temperature delivers the glass transition temperature with an accuracy of 3 K (Figure 27)... 

Temperature Coefficient of Refractive Index n The change in refractive index (n) with temperature. The degree of variation of n depends on the composition of the substance and the state of aggregation, e.g., whether it is a soKd or a liquid. It is usually about 100 X larger for Uquids than for solids and about —0.0005/°C for Kquids. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

The effects of temperature on the color development of the porous film in chlorobenzene were shown in Table 6 [23]. The coloration was reversible thermochromism. The refractive index of the materials generally decreases as the temperature increases, and the temperature dependence of the liquid is greater than that of the solid. For example, the temperature dependence (A/id/°C) of PVA and chlorobenzene was found to be 3.0 x 10 and 4.5 x 10" at 589.3 nm. Consequently, it is interpreted that the wavelength of the crosspoint between the dispersion curves of PVA and chlorobenzene shifts from the long side to the short side with increasing tem-... 

The above measurement results also included the error contribution of the temperature cross-sensitivity of the device. From Fig. 7.11, the temperature dependence of the device was 0.074 nm °C Based on (7.6), the temperature crosssensitivity of the device was less than 3.2 x 10 6 RIU °C. Therefore, the total temperature cross-sensitivity-induced measurement error was about 2.8 x 10 4 RIU in Fig. 7.13 over the temperature variation of 87°C. The temperature dependence of the device was small and contributed only about 2.3% to the total refractive index variation over the entire temperature range. 

In 10 there a great variety of materials is used, and their optical constants may be affected e.g. by film deposition technologies. What is thus required is the access to data for material dispersion with relation to technological parameter as well, either as Sellmeier or related formula, or as tabulated values. Additionally, refractive indices respond to temperature, which may be intended for device operation in case of a TO-switch, or unintended in field use. The temperature dependence of the refractive index can be attributed to the individual material, simply, but the influence of heater electrodes needs special consideration. If an 10 design-tool comes with inherent TO or EO capabilities, those effects are taken into account in the optical design directly. 

Tg can be determined by studying the temperature dependence of a number of physical properties such as specific volume, refractive index, specific heat, etc. First-order transitions, such as the melting of crystals, give rise to an abrupt change or discontinuity in these properties. However, when a polymeric material undergoes a second-order transition, it is not the primary property (the volume), but its first derivative with respect to temperature, (the coefficient of expansion), which becomes discontinuous. This difference between a first and second-order transition is illustrated in Figure 10. 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

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. 

Figure 6 Temperature dependence of the absorption spectrum of CV in ethanol. The enhancement of the OD with decreasing temperature may be due to the change in the refractive index of ethanol. (From Refs. 1, 20.)...

Figure 15.3 Temperature dependences of the linear thermal expansion, Al/l [2], refractive index, n [3] and reciprocal dielectric permittivity, 1 /x (Samara, unpublished) for pmn showing deviations from linear response at a temperature (I d) much higher than the peak (Tm) in the dielectric susceptibility (from [14]).

There is no direct information available on any possible temperature dependence of the craze refractive index. However, it might be expected that the temperature dependence is similar to that of the bulk material, which e.g. in PMMA increases by less than 1 % in the temperature range of 60 °C to —30 °C Also, measurements of the refractive index of the broken craze layer in PMMA at 25° and 60 C showed a constant value of 1.32 + 0.01 which is just the same as for the unloaded craze at room temperature. 

Refractive index fluctuates in the range 1.37 - 1.57 depending on the basic siloxane chain framework (Fig. 1). The influence of the siloxane chain framework on the refractive index was studied over a wide temperature range, and hysteresis was found on the curve of refractive index vs temperature (Fig. 2). 

Fig. 2. Temperature dependence of the refractive index of cured SIEL MPh compounds for different contents of methylphenylsiloxy units.

Properties such as volume, enthalpy, free energy and entropy, which depend on the quantity of substance, are called extensive properties. In contrast, properties such as temperature, density and refractive index, which are independent of the amount of material, are referred to as intensive properties. The quantity denoting the rate of increase in the magnirnde of an extensive property with increase in the number of moles of a substance added to the system at constant temperature... 

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