Liquid crystals nematic potential

We consider first the Maier-Saupe tlieory and its variants. In its original foniiulation, tills tlieory assumed tliat orientational order in nematic liquid crystals arises from long-range dispersion forces which are weakly anisotropic [60, 61 and 62]. However, it has been pointed out [63] tliat tlie fonii of tlie Maier-Saupe potential is equivalent to one in... 

In simple single-site liquid crystal models, such as hard-ellipsoids or the Gay-Berne potential, a number of elegant techniques have been devised to calculate key bulk properties which are useful for display applications. These include elastic constants for nematic systems [87, 88]. However, these techniques are dependent on large systems and long runs, and (at the present time) limitations in computer time prevent the extension of these methods to fully atomistic models. 

Stelzer et al. [109] have studied the case of a nematic phase in the vicinity of a smooth solid wall. A distance-dependent potential was applied to favour alignment along the surface normal near the interface that is, a homeotropic anchoring force was applied. The liquid crystal was modelled with the GB(3.0, 5.0, 2, 1) potential and the simulations were run at temperatures and densities corresponding to the nematic phase. Away from the walls the molecules behave just as in the bulk. However, as the wall is approached, oscillations appear in the density profile indicating that a layered structure is induced by the interface, as we can see from the snapshot in Fig. 19. These layers are... 

It can be safely predicted that applications of liquid crystals will expand in the future to more and more sophisticated areas of electronics. Potential applications of ferroelectric liquid crystals (e.g. fast shutters, complex multiplexed displays) are particularly exciting. The only LC that can show ferroelectric property is the chiral smectic C. Viable ferroelectric displays have however not yet materialized. Antifer-roelectric phases may also have good potential in display applications. Supertwisted nematic displays of twist artgles of around 240° and materials with low viscosity which respond relatively fast, have found considerable application. Another development is the polymer dispersed liquid crystal display in which small nematic droplets ( 2 gm in diameter) are formed in a polymer matrix. Liquid crystalline elastomers with novel physical properties would have many applications. 

The three-state RIS model of conformer statistics is used to analyze the 16 independent dipole coupling constants measured in a proton NMR study of n-hexane in a nematic liquid crystal solvent. The orientational ordering of the n-hexane molecule is treated in the context of the modular formulation of the potential of mean torque. This formulation gives an accurate description of alkane solute orientational order and conformer probabilities in the nematic solvent. Consequently, substantially more accurate calculated diplar couplings are obtained, and this is achieved without the need to resort to unconventionally high values of the trans-gauche energy difference E(g) in the RIS model. 

Abstract It is well known that spontaneous deracemization or spontaneous chiral resolution occasionally occurs when racemic molecules are crystallized. However, it is not easy to believe such phenomenon will occur when forming liquid crystal phases. Spontaneous chiral domain formation is introduced, when molecules form particular liquid crystal phases. Such molecules possess no chiral carbon but may have axial chirality. However, the potential barrier between two chiral states is low enough to allow mutual transformation even at room temperature. Therefore the systems are essentially not racemic but nonchiral or achiral. First, enhanced chirality by doping chiral nematic liquid crystals with nonchiral molecules is described. Emphasis is made on ester molecules for their anomalous behavior. Second, spontaneous chiral resolution is discussed. Three examples with rod-, bent-, and diskshaped molecules are shown to give such phenomena. Particular attention will be paid to controlling enantiomeric excess (ee). Actually, almost 100% ee was obtained by applying some external chiral stimuli. This is very noteworthy in the sense that we can create chiral molecules (chiral field) without using any chiral species. 

In comparison to nematic liquid crystals, examples of smectic liquid crystals doped with quasi-spherical nanoparticles became more elusive over the last few years. This is surprising especially considering recent work by Smalyukh et al., who found that nanoscale dispersion (based on /V-vinyl-2-pyrrolidone-capped gold nanoparticles with 14 nm diameter) in a thermotropic smectic liquid crystal (8CB) are potentially much more stable than dispersions of nanoparticles in nematics [367]. 

J. W. Emsley, S. K. Heeks, T. J. Home, M. H. Howells, A. Moon, W. E. Palke, S. U. Patel, G. N. Shilstone and A. Smith, Multiple contributions to potentials of mean torque for solutes dissolved in liquid-crystal solvents. A comparison of the orientational ordering of anthracene and anthraquinone as solutes in nematic solvents, Liq. Cryst., 9 (1991) 649-660. 

Our calculations show that to achieve good accuracy with Eqs. (4.233) and (4.234) in a wide range of temperature and frequency variations, it is necessary to retain at least five (odd k= 1, 3,..., 9) lower modes of the spectrum. We remark that the first three relaxational modes have once been evaluated both numerically [109] and analytically [82] in studies of dielectric relaxation in nematic liquid crystals, where the forms of the potential and of the basic equation coincide with those given by our Eqs. (4.224) and (4.225), respectively. 

The only flat-panel technology with the potential to pose a realistic challenge to LCDs in the medium term is OLED technology. The first factories for OLEDs using either small molecules or polymers have started production, if in relatively low volumes, see Table 1.1. Higher production volumes can be confidently expected as the market acceptability and awareness of the capability of OLEDs increases. A combination of the modulation of plane polarised light provided by an OLED back-light by an LCD to create a hybrid OLED-LCD may become a major commercial product in the near future. Oriented main-chain polymers or anisotropic polymer networks in the nematic liquid crystal-... 

In this subsection we show the effect of the orienting potential on the ESR lineshape of paramagnetic species of particular practical interest, namely, the nitroxide stearic spin probe and Cu ion complex dissolved in a nematic liquid crystal. 

F nmr spectra have been reported for tetrafluoro-l,3-dithietane in solution with nematic liquid crystals D2h symmetry is imputed. " Theoretical calculations of the transition energies and intensities of three different tetraalkyl-1,3-dithietanes indicate a need for the inclusion of d orbitals. Theoretical calculations also have been made on a dimer of 1,3-dithietane. The UV spectrum of 2,2,4,4-tetrachloro-1,3-dithietane has been interpreted with the aid of molecular orbital calculations, interaction between the two sulfur atoms is suggested. The photoelectron spectra of tetrafluoro and tetrachloro-l,3-dithietane and 1,3-dithietane itself have been reported. The negative-ion mass spectrum of tetra-fluoro-1,3-dithietane has a base peak corresponding to fluoride ion the base peak of tetra(trifluoromethyl)-l,3-dithietane corresponds to the anion of hexafluoro-thioacetone. The oxidation potential of 1,3-dithietane does not show any unusual transannular interactions in the cation radical. ... 

Reflecting on the unique features for these ternary systems, we observe that, in rejecting the random coil, the nematic phase manifests a principal characteristic of crystals in general, thus validating the term liquid crystal . It will be apparent, however, that the presence of the random coil in the system affects the composition of the anisotropic phase substantially, its absence therein notwithstanding. This is a consequence of the abundance of random coiled component in the coexisting isotropic phase it markedly increases the chemical potential of the rodlike component in that phase and, concomitantly, decreases the chemical potential of the diluent. The concentration of the rodlike component in the anisotropic phase consequently is caused to increase. 

Figure 3 Schematic Phase diagram in flow-rate and nematic potential for the three molecular flow behaviours of sheared liquid crystals...

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