N-Pentyl-cyanobiphenyl

Scheme 3. Lowest energy conformations for the mesogen 5CB (4-n-pentyl-4 -cyanobiphenyl)...

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. 

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 molecular dynamics simulation has been performed on 4-n-pentyl-4(-cyanobiphenyl (5CB) in the nematic phase. Order parameters and dipolar couplings have been calculated and used to test theoretical models. Theoretical models have also been developed to explain the shielding of a noble-gas atom in an anisotropic environment and applied to explain the medium-induced shielding of the noble gases Xe and Ne in the nematic liquid crystal 4(-ethoxybenzylidene-4-n-butylaniline (EBBA). ... 

Fig. 8 The structure of the ureidopyrimidinone (Upy) end-capped, pendant iptecene poly(p-phenylene ethylene) derivative (10) prepared by Hoogboom and Swager [72] to investigate alignment in the liquid crystal 4-n-pentyl-4 -cyanobiphenyl (5CB)...

Figure 1. Atomistic and molecular level models for rod-shaped (top) and disc-shaped (bottom) mesogens. Examples shown 4/-n-pentyl-4-cyanobiphenyl (5CB) (rod-shaped) and hexakis(n-hexyloxy)triphenylene (HAT6) (disc-shaped). (This figure is Reproduced from Ref. 16.)...

Fig. 2.6.6. Principal dielectric constants of 4 -n-pentyl-4-cyanobiphenyl (5CB) e = e,+2 2) is calculated from the measured values of e, and The dashed line denotes the extrapolated value of e,. (After reference 130.)...

The first indication that the surface-induced order in the isotropic phase of confined liquid crystals can be detected by deuteron NMR was the spectrum of selectively deuterated 4 -n-pentyl-4-cyanobiphenyl (5CB) in the spherical cavities of a PDLC material. Far above Sfi C, where the bulk turns into the isotropic phase, the spectral line (a single one) of the PDLC was considerably broader than in the bulk at the same temperature. An even more definite and surprisingly clear evidence of surface-induced order was later obtained from... 

Fig. 4.7. Relaxation time r for the fundamental twist fluctuation mode dots) as a function of sample thickness d. The aligning layer was rubbed Nylon, the liquid crystal was 4-n-pentyl-4 -cyanobiphenyl (5CB) in the nematic phase (T = 32° C). Comparison between the best fit of the theoretically derived equation (solid line) and the best fit assuming infinite anchoring strength (dashed line) is made [32].

Fast FTIR imaging showed that the diffusion of liquid crystal 4-n-pentyl-4 -cyanobiphenyl into a poly(butyl methacrylate) matrix exhibited anomalous diffusion behaviour. A fit to several models was attempted, but no single model described the observed diffusion behaviour adequately. A simple mass uptake analysis would have indicated that diffusion occurred according to Fick s second law, whereas fast FTIR correctly identified the process as anomalous. 20 refs. 

Like other states of matter, thermotropic mesophases are indefinitely stable at defined temperatures and pressures. Moreover, a thermotropic liquid-crystal-line material exhibits reversible phase transitions at well-defined temperatures. For example, the liquid crystal 4-n-pentyl-4 -cyanobiphenyl (5CB) melts from the solid to a nematic liquid crystal at 22.5°C and then from the nematic phase to the liquid at 35.0°C. As a consequence, the characterization and classification of thermotropic phases by microscopy also requires the use of an accurately controlled oven. 

With the aim of quantitatively predicting the orientational order of rigid solutes of small dimensions dissolved in the nematic liquid crystal solvent, 4-n-pentyl-4 cyanobiphenyl (5CB), an atomistic molecular dynamics (MD) computer simulation has been applied. It is found that for the cases examined the alignment mechanism is dominated by steric and van der Waals dispersive forces. A computer simulation of the deuterium NMR spectra of molecules in a thin nematic cell has been carried out and the director distribution in the cell has been studied. An experiment for the direct estimation of an element of the order matrix from H NMR spectra of strongly dipolar coupled spins that is based on the multiple quantum spin state selected detection of single quantum transitions has been proposed. The experiment also enables obtaining nearly accurate starting dipolar... 

In this section studies of dynamics at the molecular level as revealed by relaxation measurements and diffusion studies as well as the behaviour of the phase as revealed by the dynamics of the director are reported. A proton NMR relaxaometry study of the molecular dynamics in two liquid crystalline systems, namely, 4 -n-pentyl-4-cyanobiphenyl (5CB) and (S)-4 -(3-methylpenyl)-4-cyanobiphenyl (5CB ) and their mixture has been reported.The spin-lattice relaxation time has been measured as a function of temperature and Larmor frequency in the isotropic, nematic, chiral nematic, and smectic A phases of these liquid crystalline systems. The data have been analysed in terms of local and collective molecular motions. 

The effect of different response of the flexible and the rigid part of the LC molecule towards application of an electric field is not general. This is supported by results [56], where this phenomenon is detected under certain experimental conditions only. Moreover, up to now most experiments have been performed on one LC (4-n-pentyl-4 -cyanobiphenyl, 5CB) only, which has a different structure compared to the LC molecule investigated here. 

PAA, 4,4 -di-n-bialkoxy-azoxybenzene MBBA, 4-methoxybenzylidene-4 -n-butylaniline 5-CB, 4 -n-pentyl-4-cyanobiphenyl 5-OCB, 4 -n-pentoxy-4-cyanobiphenyl TBBA, terephthalylidene-bis(4-n-butylaniline) C12-BAA, C 2-benzylideneaminoazobenzene PL, potassium laurate DPPC, dipolmitoylphosphatidylcholine. 

Table 2— Physical Properties of 4-Methoxybenzylidine-4 -n-butylanaline and 4-n-Pentyl-4 -cyanobiphenyl at Room Temperature ...

Along with the above-mentioned simple model potentials, there was a detailed simulation by atomic detailed models that used the chemical structure of the molecules. The first molecular dynamics simulation of 4-n-pentyl-4 -cyanobiphenyl (5CB) had been reported in 1989 by a group at Groningen University [80]." There is a relatively recent review article that summarizes the MD calculation of liquid crystals [81]. 

Homogeneous swollen and partially swollen elastomers were prepared by immersing each dry elastomer in a solution composed of a nematic solvent and of cyclohexane. A small amount of toluene was subsequently added to the solutirai to progressively and non-destructively swell the sample. After waiting for a few hours, cyclohexane and toluene were evaporated. Most of the experiments were performed with the 4-n-pentyl-4 -cyanobiphenyl (5CB) as nematic solvent. Some additional experiments were performed with p-methoxybenzylidene p-butylanUine (MBBA), a non-polar nematic solvent. The weight concentration X of the solvent, for example 5CB, in the swollen sample is given by... 

Figure 3-7. (a) Chemical structure of aliquid crystalline compound, 4-n-pentyl-4 -cyanobiphenyl (5CB). (b) Carbon-13 chemical shift spectrum of 5CB in the nematic phase obtained via cross-polarization under static condition. Thirteen carbon sites are well resolved, (c) A 2D proton-encoded local field spectrum of 5CB in the nematic phase under static conditions. H-C dipolar coupling spectra for each carbon site are shown. Reprinted from reference 47, with permission from the Journal of Physical Chemistry... 

A typical measured autocorrelation function of the dynamically scattered light is shown in Fig. 4.5. It was obtained by using a nematic liquid crystal 4-n-pentyl-4 -cyanobiphenyl (5CB) and rubbed Nylon as aligning layer at a cell thickness of 2 qm [8]. The dots show the measured curve and the solid line the stretched exponential fit (4.20). The amplitude of the shows that the measurement was performed in a heterodyne regime as the intensity of the light scattered by fluctuations was fairly small. Therefore the characteristic... 

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