Polymer, optical property refractive index

Physical Properties. Physical properties include density, properties connected to their combustion tendency (flammability and oxygen index), optical properties (refractive index and yellow index), and the ability to absorb water. Density p, ie, the mass per unit volume, depends on the nature of atoms present in the chemical structure and the way molecules (chains) pack together. Polyoleflns, composed of C and H only, have densities in the range 0.85-1 organic polymers... 

Optical properties The most important optical properties of a material are its transparency and refractive index. Transparency is the physical property allowing the transmission of light through a material. It is important for many practical applications of polymer nanocomposites. The refractive index is the ratio of speed of the light in vacuum to the speed of light in the medium. It is the most important property of optical systems that use refraction, and its can be measured by a refractometer. 

Economics. An advantage of coextrusion is the capability of combining layers of high performance resins with low cost resin layers to produce high per-formance/low cost composite structmes. The use of recycled and scrap resins in buried layers further improves economy. Multilayer extrusion economic considerations have been calculated (89). The effect of recycle on film properties, eg, tensile strength, impact, and elongation, depends on the degree of compatibiUty of polymers in the recycle layer. Often the tie-layer polymer acts as a compatibi-lizer for recycle. Recycle of incompatible polymers with different refractive indexes usually causes haziness and cannot be used when excellent optical properties are required. 

Maximum ON-state transmittance occurs when the refractive index of polymer ( p) matches with the ordinary refractive index ( ) of LC. During the film formation, it is possible that some fraction of LC dissolved in polymer matrix can have a profound effect mi the PDLC film properties. Therefore, determination of partition of LC between the polymer and LC phases is an important factor in evaluating the performance of PDLC films. The reorientation of LC portion in a PDLC composite film is responsible for the optical non-linearity and electro-optical properties of the device. The absorption of LC into an isotropic polymer results in the LC becoming a part of the polymer phase. In this state, reorientation of LC does not happen with an applied electric field, leaving less amount of LC behind for scattering of light. Therefore, selection of suitable concentration of LC in PDLC films is crucial in optimizing film properties. LC dissolved in polymer matrix alters refractive index, dielectric constant, viscosity etc. of the host polymer. As explained earlier, for best electro-optical responses, a polymer and LC material are chosen on the basis of... 

Computed optical properties tend not to be extremely accurate for polymers. The optical absorption spectra (UV/VIS) must be computed from semiempiri-cal or ah initio calculations. Vibrational spectra (IR) can be computed with some molecular mechanics or orbital-based methods. The refractive index is most often calculated from a group additivity technique, with a correction for density. 

Various polymers, such as polythiourethanes, polythioethers, and polythioacrylates, are used to produce resins which are transparent, colorless and have a high refractive index and good mechanical properties, useful for the production of optical lenses. Higher refractive indices are promoted by sulfur compounds and especially by esters of mercaptocarboxyhc acids and polyols such as pentaerythritol (41) (see Polymers containing sulfur). 

V. Galiatsatos, R.O. Neaffer, S. Sen and B.J. Sherman, Refractive index, stress optical coefficient, and optical configuration parameter of polymers. In J.E. Mark (Ed.), Physical Properties of Polymers Handbook, Springer-Verlag, New York, 1996, p. 535. 

Many of the optical properties of a polymer are related to the refractive index, n, which is a measure of the ability of the polymer to refract or bend light as it passes through the polymer. The refractive index n is equal to the ratio of the sine of the angles of incidence, z, and refraction, r, of light passing through the polymer. 

It may happen that the properties of a monomer and its oligomers and polymers are so similar that they cannot be separated by precipitation that in the appropriate solvents the reaction mixture gels, so that dilatometry cannot be used that it becomes so opaque that neither refractive index nor optical rotation can be determined and that the reaction is too slow for normal reaction calorimetry. This situation was met when the author attempted to study the polymerisation of trimethyl and tribenzyl laevo-... 

The refractive index is the most important optical property and its effect in determining the appearance of the polymer composite has already been referred to above. Amorphous fillers such as glass fibres and beads have only one refractive index, but most mineral fillers are crystalline and have anisotropic crystal structures resulting in a number of different indices, and this can cause complex and undesirable interference effects [27]. 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

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