Mesogen 15 measuring

X-ray measurements have shown that the positional and orientational ordering in highly ordered crystalline smectic phases is more comparable with the ordering in the solid state than the structures of the fluid smectic phases and the nematic phase. Therefore, a comparison of the structures of crystals and highly ordered smectic phases is possible because of their closer similarities. Up to now, only the crystal structures of few mesogenic compounds exhibiting highly ordered smectic phases have been reported in... 

The magnetic susceptibilities of dimer liquid crystals such as NC-Ph—Ph—O—(CH2>n—Ph—Ph—CN(n 9, 10) are measured by a SQUID magnetometer. The results obtained are interpreted within the framework of the RIS approximation, the effect arising from the conformational anisotropy of the flexible spacer being strictly taken into account. The order parameters of the mesogenic core axis thus estimated are found to be consistent with those directly observed at just below 7N) by the ZH NMR technique using mesogen-deuterated samples. 

From these experiments we can conclude that the length of the flexible spacer has no measurable influence on the orientational long range order of the mesogenic side chains. If on the contrary l-l.c. s are attached to the polymer backbone, the state of order is reduced. 

From these measurements we can conclude, that at least for SA-polymer phases the mesogenic groups exhibit the same packing as known for conventional thermotropic l.c. s. But one must keep in mind that in this case the polymer backbone must participate in the anisotropic packing. 

Dynamic mechanical experiments, where the material is periodically strained, are common methods to characterize the visco-elastic behavior of elastomers by measuring the storage modulus G and loss modulus G". G is a measure for the maximal, reversibly stored energy for a periodical deformation and G" is proportional to the dissipated energy for the oscillation cycle. It is obvious to investigate, whether the l.c. state of the l.c. elastomers influences the dynamic mechanical properties and whether different modes of linking the mesogenic moieties to the backbone can be detected. 

We will discuss some preliminary results, which have been performed recently l01). In Fig. 39a the results for polymer No. 2d of Table 10 are shown, which were obtained by torsional vibration experiments. At low temperatures the step in the G (T) curve and the maximum in the G"(T) curve indicate a p-relaxation process at about 120-130 K. Accordingly the glass transition is detected at about 260 K. At 277 K the nematic elastomer becomes isotropic. This phase transformation can be seen only by a very small step in G and G" in the tail of glass transition region, which is shown in more detail in Fig. 39 b. From these measurements we can conclude, that the visco-elastic properties are largely dominated by the properties of the polymer backbone the change of the mesogenic side chains from isotropic to liquid crystalline acts only as a small disturbance and in principle the visco-elastic behavior of the elastomer... 

The study of the relaxation of dipole polarization, as well as of the dipole moments of cholesterol-containing polymers and copolymers128 "134,191 193) presents a sensitive confirmation for the existence of intramolecular structuration of mesogenic groups. This is indicated for instance, by the high values of relaxation times (Tjj p) and activation energy (EJ p) of dipole polarization, as well as by the large values of correlation parameter g, which is a relative measure of the internal rotational retardation in macromolecules (Table 18). 

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