Changes in birefringence and

In observing the time dependent changes in birefringence and stress-optical coefficient, for elongated samples at 25 C, it was found that the rate of crystallization of high trans SBR s was very much faster, some 10 times more rapid, than that for NR (8). This is consistent with the reported rates of isothermal crystallization for NR (2.5 hours at -26°C) and for 807. trans-1,4 polybutadiene (0.3 hours at -3°C) in the relaxed state (12). 

The polarizing microscope fitted with a hot stage is very useful for identifying the crystalline forms of a material. In this method, the polymorph is heated to a temperature at which it undergoes a change in birefringence and/or appearance which is characteristic of the polymorph. 

In observing the time-dependent changes in birefringence and stress-optical coefficient, for elongated samples at 25°C, it was found that the rate of crystallization of HTSBRs was very much faster, some... 

The scattering of light from a suspension of particles will cause the light transmitted through such a material to be changed in phase and amplitude. If particles are nonspheri-cal, and have a net orientation, a birefringence and dichroism will result. 

Figure 7.3. Change in birefringence [as measured by the relative Raman intensity ratio I 635 cm )/l 703 cm ) across an injection-molded polycarbonate disk cross-section (D) as a function of distance L)from the gate. Reproduced with permission from reference 10. Copyright 1986John Wiley and Sons.)...

Interest in electric field effects on macromolecules was appreciably revived when it was found that electric fields are capable of producing structural-conformational changes in biopolymers and membranes. Here, too, optical properties are a convenient indicator of field-induced processes. Initial hints of presumably chemical contributions to field-induced changes in birefringence were reported for DNA solutions of low ionic strength. Dielectric measurements have shown that polypeptides in viscous organic solvents may undergo intramolecular helix-coil transitions in the presence of electric fields. In the meantime there are many reports on field-... 

DLI curves for the end members and for the same three mixed compositions are presented In Fig. 4. Data from DLI observations correlated well with that from DSC and optical microscopy. This technique permits enhanced sensitivity when one wants to observe transitions that may involve a small enthalpy change but a discernible change In birefringence. In particular DLI Is advantageous when solid-phase polymorphism Is present In a pure compound or a mixture. 

Okano, K., Tsutsumi, O., Shishido, A. and Ikeda, T. (2006c) Azotolane hquid-crys-talline polymers Huge change in birefringence by photoinduced ahgnment change , J. Amer. Chem. Soc., 128,15368-15369. 

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