Birefringence orientation

The simplest way of establishing qualitatively the crystallinity of a polymer is by the observation of birefringence under a suitable microscope, taking care to exclude the possibility of orientation birefringence (see Sect. 2.3.3.5). Also thermotropic liquid crystalline polymers can show birefringence combined with relatively low viscosity. X-ray diffraction allows a quantitative determination of the degree of crystallinity as well as the usual crystallographic data. 

External factors scattering loss inpurities (dust, pore etc.) structureal asymmetry (aw) interface asymmetry between core and clad change in core diameter mi cropending orientation birefringence... 

Therefore, a solution-cast film is preferably employed for a protective film rather than a melt-extruded one. However, the other component of birefringence, namely out-of-plane birefringence, is generally not zero. Therefore, it has to be precisely controlled to provide a high quality display. In this chapter, the in-plane birefringence or orientation birefringence and out-of-plane... 

Conventional polymers, in general, show ordinary dispersion, in which the orientation birefringence increases with the wavelength. This behavior can be expressed by the following equation, which was proposed based on the Sellmeier relation [20-22], as follows ... 

The wavelength dispersion of orientation birefringence must be controlled precisely for color display. Based on the Kuhn and Griin model proposed for the stress-optical behavior of cross-linked rubbers, the orientation birefringence Anin(l] of an oriented polymer is expressed as follows [20, 23-27] ... 

Figure 9.1 Wavelength dependence of orientation birefringence (closed symbols] and normalized orientation birefringence (open symbols] for stretched PMMA films at draw ratios of 1.5 (circles], 2.0 (diamonds], and 2.5 (triangles].

Figure 9.2 Combination of two films having different wavelength dispersion to produce extraordinary wavelength dispersion of orientation birefringence.

Illustration of the miscible blend and random copolymerization methods to produce extraordinary wavelength dispersion of orientation birefringence. Reproduced with permission from M. Yamaguchi, M. E. A Manaf, K. Songsurang, and S. Nobukawa, Cellulose, 2012,19,601. 2012, Springer [41]. 

Among these techniques, the addition of small molecules is relatively easier than the others due to good miscibility with polymers. In contrast, the combination of species is limited for the polymer blend and copolymerization technique. Therefore, addition of small molecules is becoming a good candidate these days. Addition of needle-shaped solid particles having strong optical anisotropy also modifies the orientation birefringence and its... 

Figure 9.5 Contribution of (closed diamonds] hydroxyl and (open diamonds) acetyl groups to the orientation birefringence of (closed circles) CDA at a draw ratio of 2.0. The birefringence values of both groups are derived from the experimental results of CTA and CDA. Reproduced with permission from M. Yamaguchi, K. Okada, M. E. A. Manaf, Y. Shiroyama, T. Iwasaki, and K. Okamoto, Macromolecules, 2009, 42, 9034. 2009, ACS Publications [44].

The normalized orientation birefringence is shown in Fig. 9.7. It is demonstrated that the wavelength dependence of the normalized orientation birefringence becomes weak as the bu-... 

---