Visible light, properties

Electromagnetic radiation of which visible light is but one example has the properties of both particles and waves The particles are called photons, and each possesses an amount of energy referred to as a quantum In 1900 the German physicist Max Planck proposed that the energy of a photon (E) is directly proportional to its frequency (v)... 

The scattering of visible light by polymer solutions is our primary interest in this chapter. However, since is a function of the ratio R/X, as we saw in the last section, the phenomena we discuss are applicable to the entire range of the electromagnetic spectrum. Accordingly, a general review of the properties of this radiation and its interactions with matter is worthwhile before a specific consideration of scattering. 

Optical Properties. Teflon FEP fluorocarbon film transmits more ultraviolet, visible light, and infrared radiation than ordinary window glass. The refractive index of FEP film is 1.341—1.347 (74). 

Thin films (qv) of lithium metal are opaque to visible light but are transparent to uv radiation. Lithium is the hardest of all the alkaH metals and has a Mohs scale hardness of 0.6. Its ductiHty is about the same as that of lead. Lithium has a bcc crystalline stmcture which is stable from about —195 to — 180°C. Two allotropic transformations exist at low temperatures bcc to fee at — 133°C and bcc to hexagonal close-packed at — 199°C (36). Physical properties of lithium are Hsted ia Table 3. 

Fluorescent Dyestuffs. Very few dyes are of use in making daylight-fluorescent products. Of the dyes discovered up to 1920, only the brilliant ted and salmon dyes of the rhodamine and rosamine classes ate used in fluorescent materials in the 1990s. The first of these, Rhodamine B, was discovered in 1877. Fluorescence excited by both uv and visible light components in daylight was formally recognized as a notable property of certain dyed fabrics by the 1920s (1). 

Some physical properties of the four most common cyclodexttins are Hsted in Table 1 (3). Other important properties are (/) cyclodexttins are nonreducing (2) glucose is the only product of acid hydrolysis (J) molecular weights are always integral numbers of 162.1, the value for glucose (4) cyclodexttins are nontoxic and (5) they do not appreciably absorb ultraviolet (uv) or visible light. 

This facile reaction involves a modest change in the absorption of visible light, largely because of the visible absorption band of <7 -azobenzene [1080-16-6] having a larger extinction coefficient than azobenzene [17082-12-1]. Several studies have examined the physical property changes that occur upon photolysis of polymeric systems in which the azobenzene stmcture is part of the polymer backbone (17). 

All three techniques probe 500 A to 1 pm or so in depth for opaque materials, depending on the penetration depth of the incident light. For transparent materials, essentially bulk properties are measured by PL and Modulation Spectroscopy. All three techniques can be performed in ambient atmosphere, since visible light is used both as incident probe and signal. 

Radiation curing of epoxies with cationic initiators is well known [20—28]. UV-visible light has been the predominant radiation source the process has been limited to thin coatings due to the low penetration of the visible-UV light [22,23], Thermal and mechanical properties of these materials are low and the curing is incomplete. Several studies have shown that commercially available epoxies with various cationic initiators can be polymerized with EB curing [20,29-34]. 

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. 

Benzene is highly stable to chemical attack. )S-Carotene absorbs visible light and is orange. Both properties are direct consequences of delocalized iz systems. Delocalized n systems also affect the oxidation-reduction... 

The molecules of a molecular solid retain their individual properties. Solid I2, for example, is dark in color because individual I2 molecules absorb visible light, as shown by the fact that I2 vapor also is colored. Glucose dissolved in coffee tastes just as sweet as solid glucose because the sweet taste of glucose comes from its shape, which is the same in the solid phase as it is in solution. 

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