4-n-Octyl-4 -cyanobiphenyl

If the ratio f lf2 I is greater than unity the torques induced by the symmetric and antisymmetric strain rates respectively will never cancel out and the antisymmetric pressure will never vanish. This means that the director continues rotating for ever. The liquid crystal is said to be flow unstable and complicated flow patterns arise. TTiey have been studied comprehensively both experimentally and theoretically [30]. Some nematic liquid crystals are flow stable whereas others are not. For example, 4-n-pentyl-4 -cyanobiphenyl (5CB) is flow stable whereas 4-n-octyl-4 -cyanobiphenyl (8CB) is flow unstable. The only difference between this two substances is the length of the hydrocarbon chain attached to the cyanobiphenyl skeleton. Nematic liquid crystals that are flow stable usually become flow unstable close to the nematic-smectic A transition. The reason for this is that there is an emergent layer structure in the fluid that is incommensurate with the strain rate field. 

A typical measnrement with the nematic liquid crystal 4 — n — octyl — 4— cyanobiphenyl (8CB) is presented in Fig. 4.3. It is obvious that the thickness of the snrface induced ordered region and the amount of order increase close to the phase transition. This increase is due to the growing nematic correlation... 

Table 4.2. Comparison of anchoring energy coefficients of 4-n-pentyI-4 -cyanobiphenyl (5CB) at T = 32° C and 4-n-octyl-4-cyanobiphenyl (8CB) at T = 37° C on rubbed Nylon and photosensitive poly-(vinyl)-cinnamate. Different anchoring coefficients on rubbed Nylon are achieved by different rubbing strengths.

Abstract Surface-induced ordering of 4-n-octyl-4 -cyanobiphenyl (8CB) near the isotropic-nematic phase transition was investigated using temperature-controlled atomic force microscopy (AIM). The glass surfaces in contact with liquid crystal were modified by an adsorbed silane surfactant, a deposited 8CB mono-layer, or a deposited 8CB trilayer. 

In this paper, we explore the effect of different surface treatments upon surface-induced ordering of the liquid crystal 4-n-octyl-4 -cyanobiphenyl (8CB). Cyanobiphenyls have been intensively studied [11-13]... 

The chemical structures of the two different polymer types are given in Figure 5-9.The side-on 6 mix sample was prepared by dissolving the polymer in benzene in the presence of 10% 4-octyloxyl-4 -hexyloxybenzoate, followed by the evaporation of the solvent under high vacuum conditions. For the side-on 11 mixture 2% of 8CB (4-n-octyl-4 -cyanobiphenyl) was added as described above. In all samples, 2% of perdeuterated hexamethylbenzene (HMB- fl8) was dissolved as a nuclear spin probe. Due to the restricted diffusive motion of the probe within the liquid crystal, the probe reveals the symmetry of the particular liquid crystalline phase. The use of a spin probe rather than a deuterated mesogen itself offers the... 

Fig. 4.3. The temperature dependence of the ellipsometric coefficient at the Brewster angle pb for A — n — octyl — 4 — cyanobiphenyl (8CB). Phase transition temperature Tjvz is at 315.3 K. The solid line is a fit to (4.5) and (4.6) with...

The nematic LC is the original eutectic mixture of 35% (weight %) 4 (m-octyl oxy)-4-cyanobiphenyl (80CB) and 65% 4/-(n-pentyl)-4-cyanobiphenyl (5CB). The sample is doped with perylene and 2% (mol %) of NIAC, which is acrylate monomer containing the easily reduced l,4 5,8-naphthalenediimide moiety (see Scheme 3). Finally, 0.5% (mol %) of benzoin methyl ether (BME) is added to photoinitiate polymerization of the NIAC. 

Four liquid crystalline compounds were studied 4-/i-pentyl-4 -cyanobi-phenyl (5CB), 4-/z-octyl-4 -cyanobiphenyl (8CB), 4-/i-hexyloxy-4 -n-pentyl-a-cyanostilbene (HOPCS) and MBBA. All the compounds have the nematic phase in convenient temperature range, and, in addition, 8CB has the smectic A phase. Both 5CB and 8CB have positive dielectric... 

Daoudi et al. [83] applied the thermodynamic approach equal Gibbs energy analysis to the pressure-composition phase diagrams of binary mixtures exhibiting reentrant phase behavior. Three different solution models are tested. The experimental data for the 4-n-hexyloxy- and 4-n-octyl-oxy-4 -cyanobiphenyl system are successfully described by the regular solution hypothesis. 

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