Characteristics optical properties

Polarized light is the must powerful tool for investigating liquid crystals, all of which exhibit characteristic optical properties. A smectic liquid crystal transmits light more slow ly perpendicular to the layers than parallel to them. Such substances are said to be optically positive. Nematic liquid crystals are also optically positive, bui their action is less definite than that of smectic liquid crystals. However, the application of a magnetic field to nematic liquid crystals lines up their molecules, changing their optical properties and even their viscosity. 

Spherulites show an imperfect crystalline structure, since the melting point of the spherulite usually lies considerably below the thermodynamic melting point (see Chapter 10). Even then, a further increase in X-ray crystallinity can also be observed when the spherulites have filled the volume. Localized orientation of the crystalline region leads to the characteristic optical properties of spherulites. If spherulites are cross-linked by radiation, the identity of the individual spherulite is retained even after they have been heated above the melting point. The birefringence of oriented... 

Semiconductor nanocrystals or quantum dots (QDs) are another popular type of inorganic NPs with characteristic optical properties. QDs are typically 2-lOnm in diameter... 

Preparation of stable, zero-valent metallic copper solutions were demonstrated in either water or methanol [89]. After complexation within various surface modified poly(amidoamine) (PAMAM) dendrimers, copper(II) ions were reduced to zero valence metallic copper thus providing a bronze, transparent dendrimer-metal nanocomposite soluble in water. Solubility of the metal domains is determined by the surface properties of the dendrimer host molecules, however, their solutions still display characteristic optical properties associated with metal domains. Both aqueous and methanolic solutions of copper clusters were stable for several months in the absence of oxygen. Similar work and results were also reported by Crooks et al. [133]. 

The characteristic optical property of inertinite macerals is their comparatively high reflectance as it can be seen in Figure 3.1a-e. Although the precursors of inertinites are the same as for vitrinites, namely cellulose and lignin from plant... 

One optical feature of helicoidal structures is the ability to rotate the plane of incident polarized light. Since most of the characteristic optical properties of chiral liquid crystals result from the helicoidal structure, it is necessary to understand the origin of the chiral interactions responsible for the twisted structures. The continuum theory of liquid crystals is based on the Frank-Oseen approach to curvature elasticity in anisotropic fluids. It is assumed that the free energy is a quadratic function of curvature elastic strain, and for positive elastic constants the equilibrium state in the absence of surface or external forces is one of zero deformation with a uniform, parallel director. If a term linear in the twist strain is permitted, then spontaneously twisted structures can result, characterized by a pitch p, or wave-vector q=27tp i, where i is the axis of the helicoidal structure. For the simplest case of a nematic, the twist elastic free energy density can be written as ... 

Low pitch chiral phases have the same characteristic optical properties as thermo-... 

Methods of optical spectroscopy are especially important, because they provide plentiful information on RCs, in which pigments are involved directly in energy or electron transfer, and in which redox centers also have characteristic optical properties. ... 

The characteristic optical property of a noble metal originates from coUective excitation of conduction electrons confined in a nanometer scale these are termed... 

Characteristic optical properties of allophane thus include isotropic nature and low values of refractive index, generally below 1.5 (less than that of most clay minerals, glasses, and other minerals), differing for different composition and varying with changes due to changing water content. 

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