Ordering in liquid crystals

Of spectroscopic teclmiques, nuclear magnetic resonance (NMR) has been most widely used to measure orientational ordering in liquid crystals [M, 57 and ]. Most commonly, changes of line splittings in the spectra of... 

Marel]a S 1974 Chain ordering in liquid crystals. I. Even-odd effect J. Chem. Phys. 60 3599-604... 

Marcelja, S. (1974). Chain ordering in liquid crystals. II. Structure of bilayer membranes, Biochim. Biophys. Acta, 367, 165-176. 

In liquid crystals or LC-glasses one looks for orientational order and an absence of three-dimensional, long-range, positional order. In liquid crystals, large scale molecular motion is possible. In LC-glasses the molecules are fixed in position. The orientational order can be molecular or supermolecular. If the order rests with a supermolecular structure, as in soap micelles and certain microphase separated block copolymers, the molecular motion and geometry have only an indirect influence on the overall structure of the material. 

In 2003, Sugimoto and Kanie published what appears to be the first claim on the formation of nematic-like one-dimensional ordering in liquid crystal-nanoparticle hybrid materials. Different shapes of Ti02 nanoparticles were hybridized with two structurally different rod-like liquid crystal amines (one based on a cyanobiphenyl and a second with a fluorinated cyclohexylbiphenyl core), but only the combination of spindle-like Ti02 nanorods (with an aspect ratio greater than 10) with the... 

The reorientation of the local chain axis gives rise to the partial narrowing of the amorphous REV-8 spectra and is of a random nature. In a short period of time, a particular segment of the macromolecular chain assumes a distribution of directions which deviate from its orientation at rest. In analogy to the description of molecular ordering in liquid crystals—, we use the concept of a local order parameter for the quantitative characterization of the extent of these fluctuations. 

The atoms in crystals are not always fixed in a perfectly ordered position except at the absolute temperature Due to the thermal movement, atoms more or less deviate from their equilibrium position. For the same reason, the orientational order in liquid crystals is not perfect either. Because of the thermal fluctuation, the orientation and position of liquid crystals vary constantly. If the positions and orientations of liquid crystal molecules are frozen at a moment in time, the picture should look like that shown in Figure 1.5. The molecules tend to align along a preferred direction, but imperfectly. This preferred direction is defined as the director n. Because the molecules are moving all the time, they are not fixed at a constant... 

Ordering in Liquid Crystals Owing to Electric and Magnetic Fields... 

Transitions between a solid and a mesophase, or between two mesophases, or between a mesophase and an isotropic liquid, are thermodynamic events and are classified as either first or second order. In liquid crystals, transitions between phases are usually thought of as being weakly first order, although second-order transitions are not uncommon the melting transition is, however, first order. 

Marcelja S 1973. Molecular Model for Phase Transition in Biological Membranes Nature 241 451-453 Marcelja S 1974. Chain Ordering in Liquid Crystals. II. Structure of Bilayer Membranes. Biochimica et Biophysim Acta 367T65-176... 

There has been little development in the theory of MEM in recent years, however the diversity of applications has increased greatly. Examples include the measurement of rotameric distribution in carbohydrates, peptides,or more generally - in isotropic environments. Other applications include studies of the internal order in liquid crystals, a new attempt at the in vivo application of phase-modulated rotating-frame imaging (PMRFI),- - and a study of amphiphilic molecules in ternary systems. 

Abe, A., and Furuya, H., Molecular ordering in liquid crystals carrying flexible hydrocarbon tails a rotational isomeric state analysis of D-NMR data of Emsley et al. on 4-n-aIkyW -cyanobiphenyls (nCB), Mol. Cryst. Liq. Cryst., 159, 99-114 (1988a). 

Kronberg, B., Gilson, D. F. R., and Patterson, D., Effect of solute size and shape on orientational order in liquid crystal systems, J. Chem. Soc. Faraday Trans. 2, 72, 1673—1685 (1976). 

Samulski, E. T., and Dong, R. Y, Chain ordering and molecular orientational order in liquid crystals, J. Chem. Phys., 77, 5090-5096 (1982). 

In these electrooptic LC devices, the confining surfaces have to induce a pre-determined and well defined direction of the optical axis at the interface, that subsequently propagates into the bulk due to the long-range nature of the orientational order in liquid crystals. The solid-liquid crystal interface itself can therefore be considered as a discontinuity of the elastic and optical properties of the system. From this point of view, the interface is visible to those linear optical techniques that are enough sensitive to detect a discontinuity of the material properties across the interface. 

Pershan, P.S. Raman studies of orientational order in liquid crystals. In Luckhurst, G.R., Gray, G.W. (eds.) The Molecular Physics of Liquid Crystals, pp. 385-410. Academic, London (1979). Chapter 17... 

Chemical processes Oscillating reactions, chain reaction of catalysis, molecular self-assembly, ordering in liquid crystals, monolayers self-assembly, molecular-phase transition, Langmuir-Blodgett films, etc. 

Y. K. Fung, A. Borsmik, S. Zumer, et al., Pretransitional nematic ordering in liquid crystals with dispersed polymer networks, Phys. Rev. E, 55, 1637 (1997). 

The significance of the lack of higher orders in liquid crystals is now clear. The density variation in smectic liquid crystals is very sinusoidal, with little evidence for higher harmonics. This implies that any discussion of smectic layers and positional order within smectic planes should be accompanied with a strong reminder that in fact the variation in the density is quite smooth, varying sinusoidally with no sharp changes. 

Brock, J.D., Birgeneau, R.J., Litster, J.D., and Aharony, A. (1989) Hexatic Ordering in Liquid Crystal Films. Contemporary Physics, 30,321-335,... 

Poll, 70Luc3] Measurements of degree of ordering in liquid crystals. [75Honl] MO calculation of rt-electron spin densities McLachlan method modified. 

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