Liquid crystal host

Binary molecular co-crystals of 2,5-bis(3-pyridyl)-l,3,4-oxadiazole and 2,5-bis-(4-pyridyl)-l,3,4-oxadiazole with benzene-1,3,5-tricarboxylic and benzene-1,2,4,5-tetracarboxylic acids were studied by X-ray and thermogravimetric analysis of mass loss <2005MI1247>. Dipole moments were used to study the flexoelectric effect in guest-host mixtures of 2,5-(4-pentylbenzene)-l,3,4-oxadiazole with commercial liquid crystal hosts <2005CM6354>. The luminescence properties of many other copolymers were also investigated (see Section 5.06.12.3). 

A series of model nematic liquid crystals (among them oxadiazole derivatives) with transverse dipole moments were used to study the flexoelectric effect in guest-host mixtures with a commercial liquid crystal host <2005CM6354>. 

Certainly for real samples where the distribution function is intermediate between the isotropic and Ising limits the susceptibilities also lie between. Two interesting points can be made. 1) Disregarding variation of F, the macroscopic nonlinearity can be enhanced by up to a factor of five over the maximum achievable in isotropic media by use of liquid crystal host and 2) The nonlinearity which might be used for noncritical phase-matched SHG via the birefringence (which must depend on the magnitude of... 

Fig. 14 (a) Chemical structures of the polyphilic dispersion-promoter molecules, (b) Tailor-designed polyphilic molecules promoting CNT dispersion in the nematic host. Pyrene anchoring group (blue), mesogenic CB unit (dark red), flexible hydrocarbon or ethylene oxide spacer (green), and liquid crystal host (light red) [464]. (Reproduced by permission of The Royal Society of Chemistry)... 

Finally, our group reported on gold nanoparticles decorated with bent-core liquid crystals showing pattern formation on TEM grids after slow solvent evaporation (18 in Fig. 22). These particles showed interesting self-assembly effects in different bent-core liquid crystal hosts (SmCPA and Colr) and slightly improved electro-optic effects such as shorter response time, x, and unaltered spontaneous polarization in the SmCPA host, but no mesophase formation [547]. 

Nematic Liquid Crystal Hosts of Positive Dielectric Anisotropy... 

The first nematic guest-host prototype nematic GH-LCD reported by Heilme-ier and Zanoni " contained methyl red (157) as the dichroic dye dissolved in 4-butoxybenzoic acid as the nematic liquid crystal host. Other hosts investigated later included 4-methoxycinnamic acid and 4-ethoxy-4-aminoben-zonitrile (28), see Table 3.4. The melting point of these three single components is very high. Therefore, prototype GH-LCDs had to be operated and evaluated at very high temperatures. Thermal decomposition of the mixtures led sequentially to lower contrast, homeotropic orientation due to decomposition products and finally device breakdown. However, these initial experiments were sufficient to demonstrate the feasibility of this display type. 

T. Ikeda, T. Miyamoto, S. Kurihara, and S. Tazuke, Effect of structure of photoresponsive molecules on photochemical phase transition of liquid crystals. IV. Photochemical phase transition behavior of photochromic azobenzene guest/polymer liquid crystal host mixtures, Mol. Cryst. Liq. Cryst. 188, 223-233 (1990). 

The linear dichroism of nickel(II), palladium(II) and zinc(II) complexes of mesomorphic 4-alkoxydithiobenzoic acids has been investigated in the commercial eutectic mixture of cyanobiphenyls and cyanoterphenyls, E7 (from Merck) for the palladium(II) complexes and in the commercial mixture of cyanobicyclohexanes, ZLI2830 (from Merck) for the nickel(II) and zinc(II) complexes (Figure 2.12).For the nickel(II) and palladium(II) complexes both a ligand-based transition and a charge-transfer band (MLCT) were observed, whereas only a ligand-based transition was present for the zinc(II) complexes. These complexes had a much lower solubility in the liquid crystal host matrix than the dithiolene... 

Another approach to obtain luminescent lanthanide-containing liquid crystals is by dissolving a luminescent lanthanide complex in a suitable liquid crystal host matrix. The advantage of this method is that the luminescence and mesomorphic properties can independently be optimised. This allows easier access to nematic lanthanide-containing liquid... 

Figure 2.26 Structures of the nematic liquid crystal host matrices MBBA and 5CB, and the structure of the europium(III) complex [Eu(tta)3(phen)]...

Figure 2.27 Room temperature luminescence spectrum of [Eu(TTA)3(phen)] in the nematic liquid crystal host MBBA. The doping concentration was 4% w/w. The excitation wavelength is 396 Reprinted with permission from Binnemans...

In this section, we discuss the behavior of liquid crystal suspensions under the action of an external electric field. The behavior of colloidal suspensions in electric fields is of considerable technological interest with the so-called Electro-Rheological (ER) fluids [17, 18]. The main features of this behavior are now rather well understood. When an external field is applied, particles suspended in an isotropic fluid become polarized. Resultant dipole-dipole interactions between the particles lead to their chaining along the direction of the applied field. When suspended in a liquid crystal host, colloidal particles are also expected to be polarized upon the application of an electric field. However, new phenomena may take place because of the specific response of the liquid crystal. In this case, the external field is likely to alter the distortions of the liquid crystal alignment... 

H. Qi, B. Kinkead, V.M. Marx, H.R. Zhang, T. Hegmann, Miscibility and alignment eifects of mixed monolayer cyanobiphenyl liquid-crystal-capped gold nanoparticles in nematic cyanobiphenyl liquid crystal hosts. Chem. Phys. Chem. 10, 1211-1218 (2009)... 

Zhao and coworkers [234, 235] reported that an azobenzene polymer network can also optically align ferroelectric liquid crystals. This was done by dissolving two chiral dimethacrylate and one chiral diacrylate monomers containing azobenzene groups in a commercial ferroelectric liquid crystal host. The monomers were illustrated as follows ... 

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