Birefringence measurement, procedure

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. 

For systems where the stress-optical rule applies, birefringence measurements offer several advantages compared with mechanical methods. For example, transient measurements of the first normal stress difference can be readily obtained optically, whereas this can be problematic using direct mechanical techniques. Osaki and coworkers [26], using a procedure described in section 8.2.1 performed transient measurements of birefringence and the extinction angle on concentrated polystyrene solutions, from which the shear stress and first normal stress difference were calculated. Interestingly, N j was observed to... 

Ak can be obtained from measurements on single crystals, and provided that accurate values are available for the density, the order parameter S can be obtained directly. An alternative way to determine 5 from measurements of the temperature dependence of the susceptibility is to fit values to a functional form for the variation of S with temperature. The simplest procedure known as the Haller extrapolation is described in the context of birefringence measurements in Sec. 3.2 of this chapter. The effects of local biaxial ordering on the measured susceptibility for cyanobiphenyls has been considered by Running, Crellin and Faber [2] using crystal data for biphenyl. 

Optical properties of fibers are measured by light microscopy methods. ASTM D276 describes the procedure for fiber identification using refractive indexes and birefringence. Other methods for determining fiber optical properties have been discussed (3,38—44). However, different methods of determining optical properties may give different results (42). 

The tensile force and birefringence were simultaneously measured as functions of the strain. In brief, the samples were suspended vertically between two clamps the lower clamp was fixed, and the upper clamp was connected to a force transducer (Statham strain gauge). The output of the transducer was monitored by a Hewlett-Packard chart recorder (7, 8). Values of the birefringence An were determined by using a single-frequency He-Ne laser according to well-established procedures (2, 7, 8). Values were calculated directly from the sample thickness and the relative retardation R, which was measured with a Babinet-type compensator. The measurements on the 660-21.3 X 10 samples were carried out at 0-90 °C, and those on the 880-21.3 X 10 samples were carried out at 25 °C. 

Empirical models of the induced anisotropy have also been obtained from measurements of the pressure- and field-induced optical birefringence (Kerr effect) [20]. While these are not spectroscopic procedures, we include such references here because of their significance for CILS [20, 24-26, 52, 53]. Other modeling attempts are based on measurements of depolarization ratios as a function of pressure [163, 178, 179]. In recent work satisfactory consistency of the anisotropies derived from second virial Kerr coefficients, pressure-induced depolarization ratios, and depolarized CILS has been reported [11, 80]. We note that the confusion that has existed in the early years of CILS studies is now understood to have been due to the previous lack... 

From eqn. (14), if one can specify the values of A°n. A/if and one of the orientation functions,/ then the other may be determined by measuring A it. This procedure has been used for semi-crystalline systems where X-ray diffraction is used to determine/r, of all crystalline axes. Thus one can determine/ . a quantity which, in general, is not easy to obtain from two-component systems. The results plotted in Fig. 7 are an example of the data obtained by combining both wide-angle X-ray diffraction and birefringence to uniaxially drawn low density polyethylene. It is clear... 

A procedure is described that can measure optical phase retardations of birefrigent materials with a resolution 2x10-4 radians. The method relies on phase modulation with alternate right and left handed circularly polarized light. Phase sensitive detection is employed to reduce noise and thermal fluctuations in the optics and light source. The method is useful in Frederik s transition measurements to determine the elastic constants of weakly birefringent polymer liquid crystals with long equilibration times. 

In view of the described difficulties, it makes sense to automate the measuring setup and procedure. An imaging measuring system that facilitates rapid, spatially resolved determination of the magnitude and orientation of stress birefringence with high accuracy has been devdoped. The applied functional principle essentially corresponds to the setup indicated in Figure 2, but the analyzer is operated by a motor and the human observer is replaced by a matrix camera. 

---