Orientational order long range

Grazing incidence excitation of a fluorescent probe in a phospholipid monolayer can also be used to indicate order. The collective tilt of the molecules in a domain inferred from such measurements is indicative of long-range orientational order [222]. 

Shechtman D, Blech I, Gratias D and Cahn J W 1984 Metallic phase with long range orientational order and no translational symmetry Phys. Rev. Lett. 53 1951-3... 

The label liquid crystal seems to be a contradiction in tenns since a crystal cannot be liquid. However, tire tenn refers to a phase fonned between a crystal and a liquid, witli a degree of order intennediate between tire molecular disorder of a liquid and tire regular stmcture of a crystal. Wlrat we mean by order here needs to be defined carefully. The most important property of liquid crystal phases is tliat tire molecules have long-range orientational order. For tliis to be possible tire molecules must be anisotropic, whetlier tliis results from a rodlike or disclike shape. 

Thennotropic liquid crystal phases are fonned by anisotropic molecules witli long-range orientational order and in many types of stmcture witli some degree of translational order. The main types of mesogen are Arose tlrat are rodlike or calamitic and Arose Arat are disclike or discotic. 

Crystals are sohds. Sohds, on the other hand can be crystalhne, quasi-crystal-hne, or amorphous. Sohds differ from liquids by a shear modulus different from zero so that solids can support shearing forces. Microscopically this means that there exists some long-range orientational order in the sohd. The orientation between a pair of atoms at some point in the solid and a second (arbitrary) pair of atoms at a distant point must on average remain fixed if a shear modulus should exist. Crystals have this orientational order and in addition a translational order their atoms are arranged in regular lattices. 

Finally, whenever in matter there is no long range positional but still long-range orientational order, we have ordered liquids, instead of solids. The X-ray spectral features of an ordered liquid with a smectic structure is the occurrence of one or a few meridional sharp reflections in the fiber spectrum, plus polarized halos for an ordered liquid with nematic structure the occurrence of polarized haloes, only. 

One of the primary features of the Gay-Berne potential is the presence of anisotropic attractive forces which should allow the observation of thermally driven phase transitions and this has proved to be the case. Thus using the parametrisation proposed by Gay and Berne, Adams et al. [9] showed that GB(3.0, 5.0, 2, 1) exhibits both nematic and isotropic phases on varying the temperature at constant density. This was chosen to be close to the transitional density for hard ellipsoids with the same ellipticity indeed it is generally the case that to observe a nematic-isotropic transition for Gay-Berne mesogens the density should be set in this way. The long range orientational order of the phase was established from the non-zero values of the orientational correlation coefficient, G2(r), at large separations and the translational disorder was apparent from the radial distribution function. 

On a molecular level the director is not rigorously defined, but the molecular director is typically considered to be the average long axis of the molecules, oriented along the macroscopic director with some order parameter less than one. This type of anisotropic order is often called long-range orientational order and, combined with the nonresonant optical properties of the molecules, provides the combination of crystal-like optical properties with liquidlike flow behavior characteristic of liquid crystals. 

Taken from the three spontaneous symmetry-breaking events leading to this layer structure [formation of layers with long-range orientational order of the director (Sm), tilt of the director from the layer normal (C), and polar orientation of the molecular arrows (P)], we term phases of this type SmCP. All of the complex textures and EO behavior of NOBOW in the B 2 phase can be understood in terms of various stacking modes of SmCP layers as shown in Figure 8.23. 

Shechtman, D., Blech, T, Gratias, D., Cahn, J. W., Metallic Phase with Long Range Orientational Order and No Translational Symmetry. Phys. Rev. Lett. 1984, 53, 1951. 

Mesomorphic state having long-range orientational order and either partial positional order or complete positional disorder. 

Mesogen composed of board-like molecules with the long-range orientational order of the phase reflecting the symmetry of the constituent molecules. 

Parameter characterizing the long-range orientational order with reference to the director, with... 

Dependence of certain physical properties, like the electric permittivity, refractive index and magnetic susceptibility on direction. It is created by long-range orientational order in a mesophase, provided the corresponding molecular property is anisotropic. 

Note 2 A liquid-crystalline polymer can exhibit one or more liquid state(s) with one- or two-dimensional, long-range orientational order over certain ranges of temperatures either in the melt (thermotropic liquid-crystalline polymer) or in solution (lyotropic liquid-crystalline polymer). 

Nematic phases are characterized by an unordered statistical distribution of the centers of gravity of molecules and the long range orientational order of the anisotropically shaped molecules. This orientational order can be described by the Hermans orientation function 44>, introduced for l.c. s as order parameter S by Maier and Saupe 12),... 

As already mentioned, in the simple case of cylindrical symmetry of the mesogenic molecules, the long range orientational order of the nematic polymers can be described by Eq. (3) ... 

Plastic crystals The long-range orientational order is lost, the long-range positional order is preserved, i.e. a plastic quasi-crystalline lattice is still present. 

Lyotropic liquid crystals Due to the influence of a penetrating solvent which intercalates into the lattice, a long-range orientational order depending on the individual lyotropic phase is given, but no positional ordering can be observed. Common examples are soaps or the double layers of lipid structures. 

The nematic phase (N) is the least ordered, and hence the most fluid liquid crystal phase. The order in this type of LC phases is based on a rigid and anisometric (in most cases rod-shaped or disc-shaped) molecular architecture. Such molecules tend to minimize the excluded volume between them, and this leads to long range orientational order. For rod-like molecules the ratio between molecular length and its broadness determines the stability of the nematic phase with respect to the isotropic liquid state and the stability rises with increase of this ratio. In most cases the rigid cores are combined with flexible chains, typically alkyl chains, which hinder crystallization and in this way retain fluidity despite of the onset of order. 

Here, a paper by Smalyukh et al. stands out, which reports on nanorod alignment using likely more suitable lyotropic liquid crystals [6], The authors demonstrated spontaneous, long-range orientational ordering of CTAB-capped GNRs dispersed in lyotropic nematic and hexagonal columnar liquid crystalline phases formed by... 

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