Stress-dichroism coefficients

General quantitative relations between observed dichroic ratios and structural orientation functions have been considered by several authors. These include Fraser,Beer, Patterson and Ward, Stein, Chappel, Kawai and Stein, and Nomura et al More recently, Flory and Abe, and also Nagai, have carried out statistical calculations relating specifically to the stress-dichroism coefficients of amorphous polymer networks. Some results of these calculations will be summarised below. First, however, it is informative to derive some general relationships between the dichroic ratio and appropriate orientation functions. 

Early measurements of the IR-dichroism in stretched samples of LCEs have been described [16]. The dependence of the IR di-chroism of the CN-stretching mode was used to obtain the absorption coefficients and to extract the order parameter as a function of temperature. However, while these measurements yield reliable results inside the nematic phase, the sensitivity of this method turns out to be not high enough to analyze quantitatively the influence of the applied stress on the order parameter and on... 

Thus, in our experiments, the orientation observed through fluorescence polarization is not directly related to the complete true stress, but depends on the deformation in the rubbery plateau zone. This result is rather different from that uhich is obtained with birefringence measurements in which stress and orientation are related through a constant coefficient. Also, infra-red dichroism measurements performed in our laboratory with films issued from the same polystyrene batch lead to the... 

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