Chain compounds, birefringence

For a typical chiral organic compound, such as 2-butanol, the circular birefringence, nL - wR, at A = 589 nm is of the order of 10-7. Even for a very high a = 40° mm-1 at A = 589 nm ( wL - nR 2 X 10 4), linear birefringence, which may arise from residual ordering/aggregation of polymer chains, could easily overwhelm the circular birefringence. 

The measurement of photoinduced birefringence revealed very different anisotropy. Considering the numerous compounds that could readily be complexed with this type of polymer, including chiral adds, phenols, and metals, the approach of using side-chain azopyridine polymers offers the possibility to produce a large number of new photoactive liquid crystalline materials without exhaustive synthetic efforts and with new properties to exploit. And really the approach has been exploited in recent works. The materials similar to that... 

Although the orientation of the main chain does not directly affect the orientation birefringence for cellulose esters, it has an impact on the orientation of the ester groups as well as the hydroxyl group. Furthermore, the orientation of the main chain strongly affects the nematic interaction with low-mass compounds. 

Nobukawa and co-workers studied the effect of the aromatic compounds having various alkyl chains on orientation birefringence of CAP. The aromatic additives [C ,Ph] are synthesized from alkyl diol [m-carbons] and terephthalic acid [60,61]. 

While no liquid crystalline phase exists for the neutral compound for n = 8, a mesophase does exist within a small region for n=12. At room temperature the compound with a chain length n = 18 is a highly viscous, birefringent substance, which in two subsequent steps turns into a fluid, optically isotropic liquid. 

Myelin Cylinders. Long-chain polar compounds, above their solubility limit, may interact with surfactants to form mixed micelles that separate (as a coacervate) in the form of cylinders. These are termed myelin cylinders or myelinic figures. They are usually quite viscous and may be birefringent. 

In this chapter we shall only be concerned with electro-optic and thermo-optic switching effects in thermotropic side-chain polymer liquid crystals. We will consider briefly the synthesis and structure of such compounds and show how the nematic, cholesteric and smectic phases arise. Since the optical properties of each of these phases are different, and may be altered depending on alignment within the phase, each gives rise to different electro-optic effects. If these are coupled to the use of dye additives or substituents, then it will be realized that a wide range of electro-optic devices based on dichroism or fluorescence as well as birefringence or scattering power may be fabricated. These will be considered and discussed in terms of their performance and potential applications. Finally, possible uses of polymer-low molar mass liquid crystal solutions will be considered in terms of electro-optic device applications. 

---