Mesophases characterization

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

Polarization, and NLO properties, 12, 102 Polarized optical microscopy, metallomesogen mesophase characterization, 12, 208 Polar monomers, polymerization, 1, 147 Polar polyolefins, co-polymerizations, 11, 723 Polyacetylenes... 

The theoretical amount of mesophase (characterized by a hydrogen content of 3.5%) formed is described by the area of D-H-F for decarbonizing materials and the area of H-F-G-C for dehydrogenating materials given in Figure 7. 

The effect of the metal ion was investigated, too (Figure 27). Except for the lead complex, all complexes showed an enantiotropic, columnar mesophase characterized as Coh by miscibility studies with the zinc complex. As for the phthalocyanines, the lead ion was located out of the porphyrin plane but here, this distortion and the consequent disturbance of the tt stacking led to total suppression of the mesophase. The transition temperatures were similar for all mesomorphic metal complexes, with a perceptible effect of the metal on the clearing temperatures, which... 

A number of a-substituted-j8-diketone ((200) R = R" = Me), a-substituted-j8-ketoaldehyde ((200) R = Me, R" = H), and a-substituted-yS-dialdehyde ((200) R = R" = H) complexes were investigated to evaluate their liquid crystalline properties. Whereas none of the diketone and ketoalde-hyde copper(II) complexes was mesomorphic, bis(4-alkoxyphenylmalonaldehyde)copper and oxovanadium(rV) complexes " ((200) R = R" = H R = OC H2 +i, m > 8 for M = Cu and n > 10 for M=VO) and bis(4-alkoxyphenylmalonaldehyde)copper complexes ((200) M = Cu R = R" = H R = C H2 +i, ra>5) displayed a narrow-temperature-range ( 10°Q nematic phase above 200 °C. Some nickel complexes were also prepared but extensive decomposition hampered mesophase characterization. Fliiorination and/or chlorination at the 2- or 3-position was found to lower the transition temperature substantially in the copper complexes without destroying the nematic phase, but to inhibit mesophase formation in nickel and oxovanadium complexes. 

Other Mesophases Characterized by Conformationally Ordered Polymer Chains and No Order in the Lateral Packing... 

In conclusion, the phase behavior of symmetrically di-n-alkyl-substituted poly(silane)s and poly(silylenemethylene)s is similar both classes of polymers form the same type of mesophase, although it cannot be obtained in pure form for the poly(silylenemethylene) studied. The mobility in the mesophase, characterized by the quadmpole splitting, appears to depend strongly on the chemical structure of the backbone. For different poly(silane)s, the mobility in the crystalline phase is obviously influenced by the conformation of the backbone zW-trans vs. 73-helical) and therefore depends on the length of the side-chains. Application of pressure to poly(silane)s with 73-helical backbones leads to the formation of high-pressure crystalline modifications with dA -trans backbone conformation. The pVT studies made it possible to define the precise conditions for the pressure-induced phase transitions. 

The smectic phases form well-defined layers that can slide over one another in a manner similar to that of soap. In the smectics, the molecules are thus positionally ordered along one direction. There are several typ>es of smectic mesophases, characterized by a variety of molecular arrangements within the layers, such as smectic A (SmA), smertic B (SmB), and smectic C (SmC). In the SmA phase, the mean orientation of the molecules is parallel to the layer normal, whereas in the SmC phase it is tilted (Table 2). 

Liquid crystal systems (De Gennes P.G. and Prost J. 1993) are well defined and specific phases of matter (mesophases) characterized by a noticeable anisotropy in many of their physical properties as solid crystals do, although they are able to flow. Liquid crystal phases that undergo a phase transition as a fxmction of temperature (thermotropics), exist in relatively small intervals of temperature lying between solid crystals and isotropac liquids. 

Vittoria et al. [31,73] studied the permeability to dichloromethane vapors of hlms of SPS thermally crystallized from the amorphous phase in a form. Results showed that, for each degree of crystallinity, the fraction of impermeable phase is higher than the crystalline phase, at low vapor activity. Therefore, Vittoria and colleagues suggested that this was due to the presence of a mesomorphic phase, in addition to the crystalline and the amorphous. This mesophase, characterized by conformational order not sufficient to give rise to discrete X-ray reflections, is less permeable than the amorphous sample to the vapors at low activity and became permeable at higher activity (a > 0.6). 

As Fig. 4.11 shows, the temperature dependence of the linear growth rate of mesomorphic lamellae actually obeys Eqs. (4.1) and (4.2), and the slope of the line is equal to = 5.8 10 K. The gross rate of formation of the mesophase, characterized by constant K in the Avrami equation, can be expressed as follows [31] ... 

Reddy GSM, Jayaramudu J, Varaprasad K, Sadiku R, Jailani SA, Aderibigbe BA (2014a) Chapter 9— Nanostructured liquid crystals. In Thomas S, Shanks R, Chandrasekharakurup S (eds) Nanostructured polymer blends. WilUam Andrew, Oxford, pp 299-324 Reddy GSM, Narasimhaswamy T, Raju KM (2014b) Synthesis and mesophase characterization of novel methacrylate based thermotropic liquid crystalline monomers and their polymers. New J Chem 38 4357 364... 

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