Semicrystalline polymers optical properties

Processes such as film extrusion, fiber spinning, injection molding, and drawing tend to impart orientation to products made from semicrystalline polymers. Mechanical, dielectric, and optical properties, to mention only three, are often strongly influenced by orientation. X-ray diffraction offers a direct approach to studying crystallite orientation because the Intensity that is diffracted into a detector placed at an appropriate position is directly proportional to the number of crystal lattice planes that are in the correct orientation for diffraction. The principles of such measurements are well described in textbooks 0,2). 

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. 

The optical properties of semicrystalline polymers are often anisotropic. On the other hand, amorphous polymers are normally isotropic unless directional stresses are frozen in a glassy specimen during fabrication by a process such as injection molding. Anisotropy can often be induced in an amorphous polymer by imposing an electric field (Kerr effect), a magnetic field (Cotton-Mouton effect), or a mechanical deformation. Such external perturbations can also increase the anisotropy of a polymer that is anisotropic even in the absence of the perturbation. 

Poly(ethylene terephthalate) Poly(ethylene terephthalate) is a widely used semicrystalline polymer. The macroscopic properties of PET such as thermal, mechanical, optical, and permeation properties depend on its specific internal morphologies and microstructure arrangement. It can be quenched into the completely amorphous state, whereas thermal and thermomechanical treatments lead to partially crystallized samples with easily controlled degrees of crystallinity. The crystallization behavior of thermoplastic polymers is strongly affected by processing conditions [91-93]. 

Crystallinity is important in determining optical properties because the refiaetive index of the crystalline region is always higher than that of the amorphous component irrespeetive of whether the amorphous component is in the glassy or rubbery state. This difference in refractive indices of the component phases leads to high scattering and consequently, the translucency or haziness of semicrystalline polymers. For a purely amorphous polymer, this does not occur, and hence amorphous polymers are usually transparent. Therefore the state of polyethylene terephthalate can be explained as follows ... 

The presence of crystalline regions tends to rednce the level of light transmission, and pnre semicrystalline polymers in moderate thickness are generally translucent. They include the polyolehns, polyamides, and thermoplastic polyesters. However, several crystallizing polymers can be made into highly transparent, relatively thick prodncts. They are polymethylpentene and polyethyleneterepthalate. Films of many crystallizing polymers, particnlarly oriented hhns, can also be transparent See also optical properties. 

PP is a semicrystalline polymer whose physical, optical, and mechanical properties are determined to a great degree by its crystallinity, crystal form, and crystal structure. Under different crystallization conditions, it can form a, p, y, 5, and quasi-hexagonal crystalline forms, among which a and P are the most common. 

Despite the importance of the problem, the effect of recycling on optical properties has been marginally analysed in the literature [36]. The optical transparency in semicrystalline polymers is mainly related to the crystallinity and surface properties... 

To summarize, the control and understanding of morphology from the molecular to the macroscopic scale is crucial for optical and electrical properties and therefore also for device applications. P3HT, which has been the working horse of the polymer electronic community for many years, can be regarded as a model semicrystalline polymer for more complicated, but also more efficient, polymers based on other repeating units, e.g., donor-acceptor polymers. 

AT Dependence of I (Theory) As mentioned, NA is widely used for improving the performance of semicrystalline polymer materials, such as iPP [62,63]. NA accelerates I and generally improves the mechanical and optical properties of polymers. Most commercial NAs are made of crystalline materials [64-69], This section examines the kinetic effect of epitaxy between NA and polymer crystals [53,70-73],... 

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