Polymer characterization light birefringence

Inoue, T. and Kyu, T. (2000) Optical characterization Light scattering, birefringence, and ellipsometry, in Polymer Blends (eds D.R. Paul and C.B. Budoitdl), Wiley Sons, Ltd, Chichester, pp. 319-347. 

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

The polymer network structure can be studied by various means. Optical characterization is particularly versatile, since it can probe the composites directly and test whether, and to what degree, the network is oriented (75, 27, 30, 31), Hot-stage cross polarized light microscopy can be used to test the influence of monomer or polymer on LC phase transitions of these composites. Measurement of the birefringence of the bare polymer network, or of the LC composite in the isotropic state, yields information concerning anisotropy of the polymer network and of the type and strength of interaction between the network and LC matrix (75, 27, 30, 31). 

Figure 2 (4,5) summarizes some key points on what was the first reported and wel 1-characterized thermotropic polymer. The Eastman workers melt copolymerized p-acetoxybenzoic acid with poly(ethylene terephthalate) (PET) to form a series of thermotropic aliphatic-aromatic polyesters (X7G polymers). Some of these compositions showed the characteristic melt optical anisotropy typical of nematic small molecules, that is, the melt between crossed polaroids on a hot stage microscope transmits light. This nematic order was persistent. Of course, shear birefringence is also shown by isotropic polymer melts but light transmission decay is quite rapid. 

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