Mesogenic phase

There are some methods available for the classification of the mesogenic phases as well as the description of their structure and molecular arrangement. They must all be used together for a complete and reliable characterization. The most important are ... 

Spontaneous resolved two chiral domains are formed in equal probability. In other words, enantiomeric excess (ee) is zero. We now ask whether ee can be controlled or not. The answer is yes. Several methods used in bent-shaped mesogenic phases will be introduced. The direct method is of course an addition of chiral dopant. Actually this has been shown to be a viable method [6, 61]. Use of chiral surface is also effective [62], By using polyimide with chiral side chains at both substrate surfaces, imbalance of two chiral domains (10% ee) has been achieved. Another method using macroscopic helical structure was demonstrated by Jakli et al. [63]. They used a nonchiral polymer network, which was formed in the N phase. After the polymerization, N compounds were washed out, then bent-core mesogens were introduced. Because of the polymer helical fibers, bent-core mesogen shows a chiral domain. 

Fig. 13 The doping of a smectic C mesogenic phase with an atropoisomeric biphenyl dopant [117]...

Photoenantiomerization of different classes of organic molecules was investigated. However, the expectation that if a pure enantiomer can be racemized by light then photoderacemization of the racemate with cpl should lead to an optically active photostationary state, does not hold in all cases. Even when enantiomerization is fast, the Ae values are often too small. Molecules like 6 and 7 were extensively studied by Schuster and his group (e.g., [52,53]) in search of a molecule suited for an optical switch for mesogenic phase transitions. 

Bushby et al. were able to access similar AB stacks with derivatives of 25 using aromatic units, which are not electron-poor [86-88]. They showed that hexakis(4-nonylphenyl)triphenylene (28, n = 8) forms alternating stacks with 25 (Fig. 13). Unlike the electron-deficient derivatives mentioned previously, which exhibit single liquid crystal phases over a wide composition range of the two components, phase separation between the 25 28 and the 25 or 28 mesogenic phases occurs [89]. The driving force for the AB stack formation is a combination of a number of different non-covalent interactions which the authors termed complimentary polytopic interactions (CPIs). 

Fig. 21 a The schematic of lateral hydrogen bonding in a mesogenic phase, b The chemical structure of the fluorenone 54a and fluorenol 54b derivatives studied by Sniekus and Lemieux c Aromatic esters/amides 46a and 46b studied by Kishikawa and their proposed smectic phase assemblies... 

Direct evidence for these assignments was obtained from critical composition values obtained for two series of polyesterimides synthesised by Krichel-dorf and co-workers [76] (Table 9). In both series, a preformed unit comprising the trimellitimide of raefa-aminophenol is copolymerised with either 2-hydroxy naphthalene 6-carboxylic acid or 4-hydroxybenzoic acid. In both series, the critical value at which a mesogenic phase is first observed is 10.0, at a 1 1 composition. An isotropic phase was observed at 9.6 and below. Hence the critical value must lie between the limits of 9.6 and 10. 

Fig. 8.53 Phases of HHTT K= microcrystalline H = mesogenic, long-range order with a correlation length > 800 A Dh = mesogenic phase / = isotropic phase. From [55].

Bo Q, Yavrian A, Galstian T, Zhao Y. 2005. Liquid crystalline ionomers containing azobenzene mesogens phase stability, photoinduced birefringence, and holographic grating. Macromolecules 38(8) 3079 3086. 

For thermotropic LCs, the transition to the liquid crystal state is induced by a purely thermal process. Thermotropic LCs form thermally activated mesogenic phases that extend from the crystal melting temperature, Tm, up to the clearing or isotropic temperature, 7]. Thermotropic LCs have found wide application in the electro-optical displays [1,2]. For lyotropic LCs, the transition is induced by the influence of solvents. Lyotropic LCs exhibit their phase transitions through the addition or removal of solvent [1,2]. 

Modern gas chromatography is most often performed with high efficiency capillary (open tubular) columns coated with a cross-linked polymeric stationary phase. We provide chromatographic data on the two most common cross-linked phases (Ref. 1). These data are useful for the interpretation of chromatograms, and for quality control and assurance. The retention indices presented in these tables were measured at 120 °C isothermaUy. Retention indices are temperature dependent the temperature dependence of the Kovats indices have been studied for many compounds (Ref. 2). For more extensive information on other cross-linked phases, other silicone phases, mesogenic phases, and solid sorbents, the reader is advised to consult Ref. 1. 

Fig. 7.15. Mesogen phase correlations using well-characterized siloxanes (After...

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