Birefringence factor

Noncrystalline chain segments in fibers may also show orientation in the direction of fiber axis. The extent of this amorphous orientation can be estimated from the total orientation in combination with the crystallite orientation as obtained from x-ray analysis. Although spectroscopic, sonic, and NMR methods have been described for the determination of the general orientation, the most facile method is based on optical anisotropy [304]. This fiber property is characterized by the optical birefringence factor An, defined by the following equation ... 

The birefringence factor a is most easily obtained by measuring the optical activity of the sample [see Eq. (9)]. We measured the optical activity at the He-Ne laser frequency (6328 A) and assumed a negligible dispersion for a. For all samples, a decreased with increasing temperature. An example is shown in Fig. 4. In Table n, we list our measured values of a for the various mixtures at the temperatures where phase matching occurs. 

FIG. 4. Variation of the birefringence factor a as a function of temperature at 6328 A for the mixture of cholesteryl chloride and cholesteryl myristate (1.75 1 by wieght). The solid curve is a smooth fit to the data points. 

The birefringence of substrate materials for optical data storage devices requires special attention, especially in the case of EOD(MOR) disks. Birefringence has no importance for glass substrates (glass does not exhibit any significant birefringence) and is only a subordinate factor for polymeric protective layers of aluminum substrates because of their reflective read/write technique. 

Certainly for real samples where the distribution function is intermediate between the isotropic and Ising limits the susceptibilities also lie between. Two interesting points can be made. 1) Disregarding variation of F, the macroscopic nonlinearity can be enhanced by up to a factor of five over the maximum achievable in isotropic media by use of liquid crystal host and 2) The nonlinearity which might be used for noncritical phase-matched SHG via the birefringence (which must depend on the magnitude of... 

The solution in the extraordinary region is not birefringent, shows no evidence of physical phase separation, and shows no maxima or minima in the structure factor within the accessible range of scattering angles (30 to 135 deg). 

Birefringence induced by applied stress is caused by the two components of the refracted light traveling at different velocities. This generates interference which is characteristic of the material. The change in refractive index, An, produced by a stress S is often related by a factor C called the stress-optical coefficient as follows ... 

Figure 16.8. Relationship between the crystal orientation factor and birefringence and the draw ratio-of BPDA-PFMB fibers. 

In this respect, another insufficiency of Lodge s treatment is more serious, viz. the lack of specification of the relaxation times, which occur in his equations. In this connection, it is hoped that the present paper can contribute to a proper valuation of the ideas of Bueche (13), Ferry (14), and Peticolas (13). These authors adapted the dilute solution theory of Rouse (16) by introducing effective parameters, viz. an effective friction factor or an effective friction coefficient. The advantage of such a treatment is evident The set of relaxation times, explicitly given for the normal modes of motion of separate molecules in dilute solution, is also used for concentrated systems after the application of some modification. Experimental evidence for the validity of this procedure can, in principle, be obtained by comparing dynamic measurements, as obtained on dilute and concentrated systems. In the present report, flow birefringence measurements are used for the same purpose. 

Fig. 2.5. Steady-state and dynamic oscillatory flow measurements on a 2 wt. per cent solution of polystyrene S 111 in Aroclor 1248 according to Philippoff (57). ( ) steady shear viscosity (a) dynamic viscosity tj, ( ) cot 1% from flow birefringence, (A) cot <5 from dynamic measurements, all at 25° C. (o) cot 8 from dynamic measurements at 5° C. Steady-state flow properties as functions of shear rate q, dynamic properties as functions of angular frequency m. Shift factor aT which is equal to unity for 25° C, is explained in the text, cot 2 % and cot 8 are expressed in terms of shear (see eqs. 2.11 and 2.22)...

From the above expressions, the form birefringence and dichioism can be calculated. The form dichroism, in particular, has the simple interpretation of being the anisotropy in the second-moment tensor of the structure factor. It is also evident that the form dichroism appears at a higher order in the wave number than the form birefringence. 

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