Birefringence resulting from orientation

The adsorption double refraction results from orientated adsorption of solvent molecules on the polymer frame. There are indications that this effect plays a part in the double refraction of certain systems However, a theoretical approach to this type of birefringence does not exist. Notwithstanding these difficulties, Treloar ... 

Biaxial Birefringence Birefringence resulting from biaxial orientation. 

Figure 3 Orientation of the phenyl rings in stretched PET films, with respect to the machine (X,), transverse (X2), and normal (X3) directions, as a function of applied stress, a0, at 90°C. Birefringence results were obtained using refractrometry. Reproduced with permission from Lapersonne et al. [11]. Copyright Elsevier 1994.

Figure 4 Evolution of the orientation during and after the deformation of PS films at different temperatures above Tg. Time-resolved birefringence results with up to a 2 ms time resolution were obtained using the transmission method. Reproduced with permission from Messe et al. [15]. Copyright Elsevier 2001.

The fibers spun from nematic phase systems and solvent composition 25.0/75.0 exhibited twice the tenacity and modulus of those extruded from the system of the solvent composition 29.3/70.7. The two fiber types showed significant differences in birefringence, and in the appearance of their external surfaces and fracture surfaces. The comparable moduli of the fiber spun from a nematic solution with those of Fortisan may result from high uniaxial orientation of cellulose molecules in the former fiber. 

In all cases of practical importance, the anisotropy of solutions resulting from the combined action of dynamic and electric fields is not high the phase difference of two interfering polarized beams does not exceed 2 ir 10 . Under these conditions, the total birefringence An of the solution and the corresponding orientation angle a can be calculate according to ... 

Reliable circular dichroism spectra cannot be obtained from crystalline, oriented polypeptide material that is birefringent or scatters light. However, monolayers of protein do not appear to provide anomalous spectra (4,15), probably because of the relative uniformity of the film and the minimal refractive index increment at the protein/water interface. Nevertheless, previous results from this and other laboratories (3,16,17) have shown that albumin and fibrinogen molecules tend to lie flat, that is, with their long axes parallel to the surface, whereas globulins lie perpendicular to the surface. 

As expected, results in Fig. 15.3 show that significant fiber orientation is only achieved when the matrix is anisotropic. Similar conclusions can be drawn from birefringence measurements (made by the compensation method, using a Berek compensator) on composite films, as shown in Fig. 15.4. The birefringence is a measure of the degree of order of the matrix and therefore the good agreement between these data and those obtained from SALS (S) reveal the excellent compatibility between the matrix and the fibers, which results from a similarity between the chemical structure of both components of the composites. 

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