Optical Properties of Polydomains

Similar results for this stress-optical coefficient were obtained for a different family of LCEs [2]. In addition it was shown that the birefringence, An, is linear in the applied stress for the range of temperatures investigated, a result one would expect on the basis of linear stress optics these results are summarized in Fig. 7. 

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 

Stress-optical experiments on cylindrical samples under uniaxial compression have also been performed [5]. It was found 

The results and the analysis of detailed stress-optical measurements in the immediate vicinity of the phase transition have been reported [3,4]. In Fig. 8 the reciprocal 

Detailed stress-optical measurements have been analyzed to yield further information [4]. In Fig. 10 the birefringence (order parameter) was plotted as a function of reduced temperature for several nominal stresses 7 . These results were combined with the predictions of the Landau model and static stress-strain curves and led to a number of interesting consequences. In Fig. 11 the shift in the phase transition temperature is plotted as a function of nominal stress and shifts of up to 7.5 K were found compared to maximum displacements by electric and magnetic fields of about 5 mK in low molecular weight materials. In Fig. 12 the birefringence An is shown as a function of strain X=L/Lq at constant nominal stress f7n = 2.11xlO Nmm. A strictly 

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Cross-linked liquid crystalline polymers with the optical axis being macroscopically and uniformly aligned are called liquid single crystalline elastomers (LSCE). Without an external field cross-linking of linear liquid crystalline polymers result in macroscopically non-ordered polydomain samples with an isotropic director orientation. The networks behave like crystal powder with respect to their optical properties. Applying a uniaxial strain to the polydomain network causes a reorientation process and the director of liquid crystalline elastomers becomes macroscopically aligned by the mechanical deformation. The samples become optically transparent (Figure 9.7). This process, however, does not lead to a permanent orientation of the director. 

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