Mesomorphic behaviour

Note 2 A polymer composed of molecules that have rigid rod-like groups or chains usually does not show thermotropic mesomorphic behaviour because decomposition occurs below its melting point. 

Liquid crystals with a large molecular mass are able to form a glassy state with mesomorphic behaviour. Yitzchaik and coworkers38 report about a new class of copolymers with non-linear optical properties, and a monomeric representative with a glassy metastable... 

Supramolecular chemistry can be used to create the bent cores that give rise to the symmetry breaking in this family of liquid crystals [139]. The formation of a complex between a calamitic benzoic acid derivative and a bent core terminated with a pyridyl group—neither of which display mesomorphic behaviour—gave rise to a material which displayed SmCP mesophases. The achiral bent cores can also give rise to symmetry breaking when they are attached to flexible polymeric chains, such as poly(siloxane) [140]. 

Dopes like these exhibit mesomorphic behaviour they are solid at room temperature, but at higher temperature become less viscous and show optical anisotropy. If heated further, the clearing temperature (Td) is reached at which a phase transformation takes place from an anisotropic solution to an isotropic solution. With increasing polymer concentration both Ta and the melting point of the dope (T ) increase. Fibres of the highest quality (tenacity) are obtained by spinning at temperatures between and Ta, but as low as possible, The spun filament is solidified in a coagulating bath, preferably at temperatures below 5 °C. 

Causin V, Saielli G (2009) Effect of asymmetric substitution on the mesomorphic behaviour of low-melting viologen salts of bis(tiifluoromethanesulfonyl)amide. J Mater Chem 19 9153-9162... 

From the above results, it is clear that the presence of classical mesogens is not necessary for linear chains like poly(di-n-alkylsilane)s or poly(di-n-alkoxyphos-phazene)s [77] to show a mesomorphic behaviour. This concept has also been applied to the case of poly(di-n-alkylsiloxane)s. For aUcyl chains containing between 2 and 6 carbon atoms, the materials were shown to form a columnar mesophase, in which the molecules are positionally and orienta-tionally ordered in a two-dimensional hexagonal lattice, but along the chain no long range correlations exists [78]. The most famous member of this series of polysiloxanes is polydiethylsiloxane which exhibits at room temperature a... 

This reflects that one of the key parameters, which has to be tuned in order to stabilize the mesomorphic behaviour of these compounds, is an efficient Ailing of the space around a rigid skeleton of stacked polar cores within a columnar structure. 

Furthermore, the mesomorphic behaviour of some complexes, such as 20, can be very comparable with that of the free ligand (the azoxy ligand of 20 possess a nematic phase between 80 and 126 °C), The cyclopentadienyl cyclopalladated complexes mainly show nematic phases, although with wider temperature ranges and at lower temperatures than the acetylacetonate complexes. 

Quite unusually for homologous series of thermotropic polymers, the samples with odd-numbered segments, except 2 (m=3), did not show a mesomorphic behaviour. While acknowledging that liquid crystal properties might be highly molecular weight dependentJ this appears as a clear indication that in polymer, or oligomer, systems the onset of a mesophase may be limited to discrete values of m. 

It is evident that bridging units that serve to expand the anisotropic polarizability, while preserving the rigidity and linearity, of the rod-like core are most suitable in promoting a mesomorphic behaviour ... 

J.H. Wild, K. Bartle, M. O Neill, S.M. Kelly and R.P. Tuffin, Synthesis and mesomorphic behaviour of wedge-shaped nematic liquid crystals with flexoelectric properties, Liq. Cryst. 33(6), 635-644, (2006). 

Akutagawa, T. Matsunaga, Y. Yasuhara, K. Mesomorphic behaviour of 1,3-phenylene bis[4-(4-alkoxyphenyliminomethyl)benzoates] and related compounds. Liq. Cryst. 1994, 17, 659-666. 

Lee, S. K. Naito, Y Shi, L. Tokita, M. Takezoe, H. Watanabe, J. Mesomorphic behaviour in bent-shaped molecules with side wings at different positions of a central naphthalene core. Liq. Cryst. 2007, 34, 935-943. 

Reddy, R. A. Sadashiva, B. K. Unusual mesomorphic behaviour in bent-core compounds derived from 5-cyanoresorcinol. Liq. Cryst. 2004, 31, 1069-1081. 

C. The mesomorphic behaviour of some truxene systems is rather odd. For example, compound 12 exhibits an inverted phase sequence where the phase is exhibited at a... 

In low molar mass systems there are maity fascinating trends of mesomorphic behaviour and so this should also be seen in polymeric analogues. The additional ordering on polymerisation causes liquid crystal phases to be more ordered than for the monomeric analogue and transition temperatures and clearing points are higher. Accordingly, if a... 

The previous discussions on the effect of spacer unit and the effect of mesogenic unit on mesomorphic behaviour were illustrated using a small range of polymer backbones. 

Table 11. Mesomorphic behaviour of a variety of arylcyclohexylidene ethanones.

Many books and review articles have been written on liquid crystalline structures and their mesomorphic behaviour [1-7]. 

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