Birefringence applications

The radial configuration occurs when the liquid crystal molecules are anchored with their long axes perpendicular to the droplet wall (Figure 3B). The radial droplet is not birefringent. Application of an external field switches the radial droplet to an axial configuration. As with the bipolar case the films switch from scattering to transparent upon application of an electric field if np=n0. 

A macroscopic, quantitative way to analyze birefringence is through Jones (33-40) and Mueller (41) calculus and the Poincare sphere (42). Those tools are widely used in the optical industry and references on them abound. Another active field of birefringence applications is the combination of the technique with polymer rheology, called flow-birefringence (43,44). 

The TPX experimental product of Mitsubishi Petrochemical Ind. (221) is an amorphous, transparent polyolefin with very low water absorption (0.01%) and a glass-transition temperature comparable to that of BPA-PC (ca 150°C). Birefringence (<20 nm/mm), flexural modulus, and elongation at break are on the same level as PMMA (221). The vacuum time, the time in minutes to reach a pressure of 0.13 mPa (10 torr), is similarly short like that of cychc polyolefins. Typical values of TPX are fisted in Table 11. A commercial application of TPX is not known as of this writing. 

Alicyclic dianhydrides are interesting for electronic applications. The polyimides obtained from them are colorless with high transparency in the visible range, exhibit low birefringence,125 and have a low dielectric constant.126 The reactivity of the polycyclic aliphatic dianhydride has been investigated. For example, bicyclo-[2,2,2]-oct-7-ene tetracarboxylic dianhydride reacts quickly with an aromatic amine because the bicyclo-imide is less strained than the corresponding dianhydride.127... 

The effects of dispersion and birefringence on stellar interferometry will be discussed in Sections 17.2.3 and 17.2.4. New kind of fibres has been design to manage the dispersion properties using a silica / air structure. These fibres, so called Photonic Crystal Fibres, are very promising for many applications (Peyrilloux et al., 2002). 

Lagorceix, H., Reynaud, R, 1995, Squeezing highly Birefringent Fiber for an Accurate Nondestructive Determination of Principal-Axis Orientation along the Waveguide application to Fiber Babinet Compensator Implementations Optical Fiber Technology 1, 171... 

Application of a field to the ShiCaPa phase causes switching by precession of the director around the tilt cone in alternate layers, to give a ferroelectric ShiCsPf state with uniform tilt. In this case, there can be no domains of opposite tilt since such domains would necessarily have their polarization opposing the applied field. This leads to a uniform SmC-like texture with a green birefringence color. The extinction brushes in the cylindrical focal conic rotate counterclockwise when the net tilt rotates clockwise, as indicated in Figure 8.25. As anticipated, the chiral rotation of the brushes is a direct manifestation of the chirality of the phase. Elsewhere in the sample there must be ShiCaPa domains of opposite handedness, which would possess the opposite sense of tilt for the same sign of the applied field. 

In addition to the above three effects, there are two others i.e, memory birefringence and depolarization scattering, which exist in the PLZT materials and have been proposed for device applications. These are described in reference 5. 

In the same way that close-packed directions in a crystal have larger refractive indices, so too can the application of a tensile stress to an isotropic glass increase the index of refraction normal to the direction of the applied stress. Uniaxial compression has the reverse effect. The resulting variation in refractive index with direction is called birefringence, which can be used as a method of measuring stress. 

Of the three physical properties covered in this chapter, optical properties have the least importance in composite and biological applications. This is not to say that there are no applications of optical properties in composites or biological materials. There are indeed, such as the use of birefringence in the analysis of stress distribution and fiber breakage in fiber-matrix composites [14] and in the development of materials for ophthalmic implants such as intraocular devices [15]. These topics are beyond the scope of this text, however, even as optional information, and introduce no new concepts from a material property standpoint. There are many interesting articles and... 

The most common applications of DSC are to the melting process which, in principle, contains information on both the quality (temperature) and the quantity (peak area) of crystallinity in a polymer [3]. The property changes at Tm are often far more dramatic than those at Tg, particularly if the polymer is highly crystalline. These changes are characteristic of a thermodynamic first-order transition and include a heat of fusion and discontinuous changes in heat capacity, volume or density, refractive index, birefringence, and transparency [3,8], All of these may be used to determine Tm [8],... 

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