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Nematic phase thermotropic liquid crystals

Since that review, Chen et al. have reported on the supramolecular interaction of polyethyleneimines with carboxylic acids, which form through proton transfer from the acid to the imine groups. Thermotropic liquids crystal nematic phases were observed for those PILs at temperatures between 58 and 138 °C. [Pg.19]

Hamley I W, Garnett S, Luckhurst G R, Roskilly S J, Pedersen J S, Richardson R M and Seddon J M 1996 Orientational ordering in the nematic phase of a thermotropic liquid crystal A small angle neutron scattering study J. Chem. Phys. 104 10 046-54... [Pg.2568]

The prime requirement for the formation of a thermotropic liquid crystal is an anisotropy in the molecular shape. It is to be expected, therefore, that disc-like molecules as well as rod-like molecules should exhibit liquid crystal behaviour. Indeed this possibility was appreciated many years ago by Vorlander [56] although it was not until relatively recently that the first examples of discotic liquid crystals were reported by Chandrasekhar et al. [57]. It is now recognised that discotic molecules can form a variety of columnar mesophases as well as nematic and chiral nematic phases [58]. [Pg.93]

Thermotropic liquid crystals, 15 86-98 bent-core, 15 98 discotic phases of, 15 96 frustrated phases of, 15 94-96 metallomesogens, 15 97 nematic liquid crystals, 15 86-92 smectic liquid crystals, 15 92-94 Thermotropic mesophases, 20 79 Thermotropic polycarbonates, 19 804 Thermotropic polyesters, liquid-crystalline, 20 34... [Pg.944]

When they are heated, mesogenic compounds do not melt directly from the highly ordered crystalline state to an isotropic liquid. They form instead, intermediate phases in which the molecules are orientated in a parallel direction and referred to as smectic (centers of the molecules organized in layers) or nematic (centers of the molecules distributed at random). Smectic and nematic mesophases are in turn divided into a variety of subgroups of thermotropic liquid crystals which will not be dealt with in detail in the present article. [Pg.279]

We note that earlier research focused on the similarities of defect interaction and their motion in block copolymers and thermotropic nematics or smectics [181, 182], Thermotropic liquid crystals, however, are one-component homogeneous systems and are characterized by a non-conserved orientational order parameter. In contrast, in block copolymers the local concentration difference between two components is essentially conserved. In this respect, the microphase-separated structures in block copolymers are anticipated to have close similarities to lyotropic systems, which are composed of a polar medium (water) and a non-polar medium (surfactant structure). The phases of the lyotropic systems (such as lamella, cylinder, or micellar phases) are determined by the surfactant concentration. Similarly to lyotropic phases, the morphology in block copolymers is ascertained by the volume fraction of the components and their interaction. Therefore, in lyotropic systems and in block copolymers, the dynamics and annihilation of structural defects require a change in the local concentration difference between components as well as a change in the orientational order. Consequently, if single defect transformations could be monitored in real time and space, block copolymers could be considered as suitable model systems for studying transport mechanisms and phase transitions in 2D fluid materials such as membranes [183], lyotropic liquid crystals [184], and microemulsions [185],... [Pg.63]

Thermotropic liquid crystals come in two types calamitic and discotic. Calamitic phases (from the Greek for tube ) are all those that are caused by rod-like mesogens. The more recently characterised discotic phases are caused by disc-like species. Calamitic phases may be either nematic (from the Greek for thread ), smectic (from the Greek for soap ) or cholesteric (named after the cholesterol derivatives such as 13.4, which exhibit this behaviour). [Pg.872]

Thermotropic liquid crystals can then be furflier subdivided into high molecular mass, main and side-chain polymers [10] and low molecular mass, the latter class of compounds being one of the areas of this review. The phases exhibited by the low molecular mass molecules are then properly described with reference to the symmetry and/or supramolecular geometry of the phases, which are briefly introduced here and are discussed in more detail further below. Thus, the most disordered mesophase is the nematic (N), which is found for calamitic molecules (N), discoidal molecules (Nq) and columnar aggregates (Nc), among others. The more ordered lamellar or smectic phases (S) [11, 12] are commonly shown by calamitic molecules, and there exists a variety of such phases distinguished by a subscripted letter (e. g. Sa, Sb)- Columnar phases (often, if incorrectly, referred to as discotic phases) may be formed from stacks of disc-like molecules, or from... [Pg.286]

Liquid crystalline phases can show not only long-range orientational order as nematic phases do but also long-range positional order. When this positional order is one-dimensional, the mesophase is called lamellar or smectic when it is two-dimensional, it is called columnar. The latter case is often found with thermotropic liquid-crystal disk-like molecules. Such molecules stack in columns that assemble on a 2-D lattice of hexagonal, rectangular, or oblique symmetry. The molecules in a given column only show 1-D liquid-Hke order and the uncorrelated columns are free to slide past each other, which ensures the mesophase fluidity [73]. [Pg.147]

N. Boden, Y. K. Levine, D. Lightowlers, and R. T. Squires, "NMR dipolar echoes in liquid crystals," Chem. Phys. Letters 31, 511 (1975) "Internal molecular disorder in the nematic and smectic phases of thermotropic liquid crystals studied by NMR SPDE experiments," ibid 34, 63-68 (1975). [Pg.255]

Liquid crystals are broadly classified as nematic, cholesteric and smectic (I)- There are at least nine distinct smectic polytypes bearing the rather mundane labels smectic A, B, C,... I, by the chronological order of their discovery. Some of the smectics are actually three-dimensional solids and not distinct liquid-crystal phases at all. There are three t s of liquid crystals. Thermotropic liquid-crystal phases are those observed in pure compounds or homogeneous mixtures as the temperature is changed they are conventionally classified into nematic, cholesteric, and smectic phases in Fig.2. Lyotropic liquid-crystal phases are observed when amphiphilic molecules, such as soaps, are dissolved in a suitable solvent, usually water. Solutions of polymers also exhibit liquid-crystalline order, the polymeric phases. Most of our knowledge about liquid crystals is based on the thermotropic phases and much of this understanding can be transferred to elucidate polymeric and lyotropic phases. [Pg.63]

To learn the effect of shear on the spectra, the zero shear rate spectra and the spectra under shear were plotted together for the thermotropic liquid crystal (LC2) in Fig. 14. There were no significant spectral changes with shear. The major peaks did become a little sharper. The spectra corresponding to the smectic A (55 C) and the nematic phase (70"C), shown in Figs. 14 and b respectively, bear this out. [Pg.71]

Thermotropic Liquid Crystals. - Organic molecules, having aromatic rings or unsaturations thus producing elongated shapes, and also polymeric molecules often show thermotropic phase behavior. Mesomorphism comprises typically nematic, smectic A and B, and cholesteric thermotropic phases, but in several cases columnar, discotic and rod-disk self-assembly shapes of thermosensitive mesogens have been observed. [Pg.525]

There are two principal categories of mesophases, thermotropic and lyotropic. Thermotropic liquid crystals are formed within a particular range of temperature in a molten material, with no solvent present, whereas lyotropic liquid crystals are formed by some substances when they are dissolved in a solvent. Within each of these categories there are three distinct classes of mesophases, which were first identified by Friedel in 1922. The simplest of these to describe are the nematic and smectic classes, illustrated schematically in fig. 12.16. These phases are formed by long thin rigid molecules which tend to line up parallel to each other. [Pg.371]

The first ferrocene-containing thermotropic liquid-crystals, i.e., compounds (284) to (286), were reported by Malthete and Billard in 1976, with enantiotropic (for (284)) or monotropic (for (285) and (286)) nematic phases being observed. Compounds (284) to (286) were designed specially to... [Pg.585]


See other pages where Nematic phase thermotropic liquid crystals is mentioned: [Pg.211]    [Pg.6]    [Pg.346]    [Pg.397]    [Pg.85]    [Pg.934]    [Pg.179]    [Pg.131]    [Pg.477]    [Pg.49]    [Pg.662]    [Pg.354]    [Pg.122]    [Pg.251]    [Pg.252]    [Pg.282]    [Pg.477]    [Pg.212]    [Pg.523]    [Pg.316]    [Pg.336]    [Pg.270]   
See also in sourсe #XX -- [ Pg.12 , Pg.199 ]




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Crystal phases

Isotropic-nematic phase transition thermotropic liquid crystals

Liquid crystal phase

Liquid crystals nematic phase

Liquid nematic

Liquid thermotropic

Nematic crystal

Nematic liquid crystals

Phase nematic

Phases nematic phase

Thermotropic liquid crystal phases

Thermotropic liquid crystals

Thermotropic liquid crystals chiral nematic phase

Thermotropic liquid crystals nematics

Thermotropic nematic phases

Thermotropic phases

Thermotropism

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