Mesophase optical texture detected

Composition of Parent Pitch. Once the chemical composition of the carbonizing system moves away from the comparative simplicity of polynuclear aromatic hydrocarbons to that of industrial pitches, then the pyrolysis chemistry incorporates effects caused by the presence of heteroatoms (0, N and S) and alkyl and naphthenic groups. In general terms, the system becomes more Reactive creating higher concentrations of radicals detectable by ESR. This in turn, leads to enhanced cross-linkages and polymerization of molecular constituents of any mesophase which is formed, and this causes enhanced viscosity and a reduction in size of optical texture. 

Tetracatenars 2mm-2mm Within the homologous series with a six-benzene-ring core 26 [24], only one type of mesophase has been detected by optical observations. The textures are fan-shaped, with developable domains in every way similar to those of the Oh phase of tetracatenars 2mp-2mp. As an example, for the compound with n = 10 K 76 °C Oh 110 °C I. Despite the unusual length of the central rigid part, the transition temperatures are surprisingly low (Table 10), a fact evidently connected with the meta position of all the alkyloxy chains. 

Cubic phases (Cub) are mesophases of cubic symmetry (Diele, 2002). Because of their high symmetry, their physical properties are no Imiger anisotropic. No defect texture is observed by polarizing optical microscopy (POM vide infra) and the image between crossed polarizers remains black. The cubic mesophases are very viscous and often their formation kinetics is very slow. Although cubic mesophases are very common for lyotropic LCs, where a cubic phase is possible between any pair of phases, there are only relatively few examples of cubic mesophases in thermotropic LCs. Whereas a cubic mesophase can be relatively easily detected when it is present between two anisotmpic mesophases, it is difficult to observe the formation of the cubic phase when it is formed by cooling an isotropic liquid. In this case, a deformatirMi of air bubbles in the melt is observed, as well as a sharp increase in the viscosity of the liquid. 

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