Mesogens, disc-like

All Liquid Crystal Polymers are characterised by the fact that they contain stiff meso-genic groups, often inserted in flexible chain systems (so called "spacers") and connected to them by linking functional groups the mesogenic unit is inserted either in the main chain or in the side chains or (in exceptional cases) in both. We shall discuss MCLCPs and SCLCPs. A schematic representation of common structures of LCPs is displayed in Fig. 6.14 (Jansen, 1996). An example of a SCLCP with disc-like mesogens is displayed in Fig. 6.15 (Franse et al., 2002, 2004). 

Ortho-substitution is also used to prepare branched liquid crystalline polyethers of 3,4-(di-n-alkoxy)benzyI derivatives in which the cyclotetraver-atrylene disc-like mesogen is formed in situ during the polymer-forming Friedel-Crafts alkylation, [30-32],... 

Ringsdorf s research group have prepared novel types of rigid-rod polyesters and polyamides 56 with a disc-like mesogen in tte mainchain [75]. Most polymers with six lateral substituents appear to be thermotropic liquid crystals. Polyamides with Z = H and having four substituents on the diamine component are not liquid crystalline. The two substituents on the diacid component seem to contribute to decrease further the intermolecular hydrogen bonding. 

Dibenzofulvene 26 Disc-like mesogens 216 Dispersion polymerimation 53, 63 Dodecylester of sodium sulfosuccinate acid 50... 

Herrmann-Schonherr O, Wendorff JH, Ringsdorf H, Tschirner P (1986) Structure of an aromatic polyamide with disc-like mesogens in the main chain. Makromol. Chem. Rai d Commun. 7 791... 

Fig. la-e. Sketches of the possible molecular architectures for liquid crystal dimers a symmetric calamitic dimer b non-symmetric calamitic dimer c symmetric discotic dimer d non-symmetric discotic-calamitic dimer e laterally linked symmetric dimer. Ellipses represent rod-like mesogenic groups, circles disc-like mesogenic units and wavy lines denote the flexible spacers... 

Fig-1.1.9. Polymers that exhibit liquid crystalline phases. The basic monomer units are low molar mass rod-like or disc-like mesogens which may form part of the main chain (a) or attached as side groups (b). 

In the preceding chapters the synthesis properties of linear liquid crystalline polymers are described, where different approaches exist to obtain the liquid crystalline state rod-like or disc-like mesogenic units are either incorporated in the polymer backbone or are attached as side groups to the monomer units of the main chain. Following conventional synthetic techniques these linear polymers can be converted to polymer networks. Compared to low molar mass liquid crystals and linear liquid crystalline polymers, these liquid crystalline elastomers exhibit exceptional new physical and material properties due to the combination and interaction of polymer network elasticity with the anisotropic liquid crystalline state. 

Disc-Like Mesogen Coated Gold Nanoparticles... 

Of all liquid crystalline phases, the nematic phase is the phase with the highest symmetry, i.e. Dooh, and the least order. As shown in Fig. 3.3a, b, the mesogens solely possess orientational order. Positional order of the mass centers does not occur in this phase. Nematic phases are usually built up by either rod-like or disc-like mesogens. For thermotropic liquid crystals these mesogens are therefore calamitic or discotic molecules, respectively. In both cases the phase is simply denoted with the abbreviation N. For lyotropics, the notation typically distinguishes between nematic phases Nc, which are formed by rod-like micelles, and nematic phases Np, which are composed of disc-like micelles. 

As illustrated in Figure 5.2, SCLCPs can also be generated by using a disc-like mesogenic side chain unit. The triphettylene imit is commotdy used to generate discotic mesophases, and when incorporated into a poly(siloxane), a discotic mesophase is exhibited (compound 37). 

The combination of the flexible siloxane backbone and the rather bulky nature of the disc-like mesogenic side chain generates a very low glass transition temperature (T. ... 

Destrade, C., Nguyen, H.T., Gasparoux, H., Malthete, J., and Levelut, A M. (1981) Disc-like mesogens a classification. Molecular Crystals and Liquid Crystals, 71, 111-135. 

Figure 5.7 Examples of disc-like mesogens, together with phase transition temperatures (°C)...

Pressure-temperature phase diagrams of the disc-like mesogens benzene-hexa-n-... 

In contrast to the single kind of fluid nematic phase known to be exhibited by calamitic mesogens, the disc-like mesogens described in this Datareview can fmm two nematic phases, each showing a Schlieren texture a discotic nematic or a columnar nematic type of phase both differ in their supra-molecular array of the disc-like molecules and viscosity. 

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