Liquid-crystal lyotropic

Lyotropic liquid crystals are made up of two or more components. Generally, one of the components is an amphiphile (containing a polar head group attached to one or more long hydrocarbon chains) and another is water. A familiar example of such a system is soap (sodium dodecyl sulphate) in water. As the water content is increased several mesophases are obtained. The types of molecular packing in these mesophases are represented schematically in figs. 1.2.1 and 1.2.2, but several modifications of these structures exist.  

In hydrophobe-dominated compositions, such as aerosol OT-water systems, inverted middle and inverted viscous isotropic phases can occur in which the tails point outward towards the hydrophobic medium while water is trapped inside.  

Two mesophases may coexist over small ranges of composition and temperature. Phase diagrams have been constructed for a large number of binary systems. Transitions may be brought about from any one of the mesophases directly to the isotropic solution at appropriate temperatures. Ternary and higher-component systems exhibit essentially the same types of structures, the phase diagrams being of course much more complicated. 

Cholesteric liquid crystals are formed by solutions of synthetic polypeptides, e.g., poly-y-benzyl-L-glutamate, in organic liquids when the concentration exceeds a certain critical value.  

Lyotropic liquid crystals occur abundantly in nature, being ubiquitous in living systems.Their structures are quite complex and are only just beginning to be elucidated. However, in this monograph we shall be confining our attention mainly to the physics of low molecular weight thermotropic liquid crystals and do not propose to discuss polymer and lyotropic systems in any further detail. In chapters 2-5, we deal with the nematic, cholesteric and smectic mesophases of rod-like molecules and in chapter 6 discotic systems. 

Liquid crystal phases also appear in response to changes in the concentration of water, oil, surfactants, or other species in a wide variety of molecular mixtures. These are called lyotropic liquid crystals. 

Lyotropic liquid crystals consisting of long rigid molecules 

A few non-amphiphilic molecules are able to show liquid crystallinity in solution at a certain range of concentration, such as PBLG, DNA, the tobacco mosaic virus, etc. They are of great molecular mass, very rigid, rod-like and have a very long anisotropic shape. They are typical macromolecules and are lyotropic liquid crystals. This class of liquid crystals does not aggregate to form sphere, column or laminar structures. These lyotropic systems depend on the properties of the solvent. They are one of major interest of this book and will be discussed in detail later. 

For low molecular weight surfactants the capability to form lyotropic liquid crystals (LC) in water is an essential property [318]. Although the appropriate temperature and concentration ranges of the liquid-crystalline mesophases can be small, mesophases are always found when carefully searched for. 

In this light, it is not surprising that there are many reports on polymeric lyotropic LCs formed by polysoaps at high concentrations [62, 63, 70, 87, 121-124, 126, 172, 173, 178, 230, 231, 240, 244, 249, 261, 300, 331, 398-404], particularly when polymerized surfactants are involved (Figs. 36, 37). 

As for low molecular weight surfactants, the superstructures are assumed to be formed by micellar aggregates [126], But it seems that the formation of lyotropic liquid crystals is supported by the additional presence of thermotropic mesogens [87,122-124,126], Lamellar, hexagonal, cubic and even nematic and cholesteric mesophases were reported for binary systems, the latter being exceptional. Lyotropic mesophases were also observed in non-aqueous solvents [240,400,401,405], If polymerizable surfactants are studied, not only the phase diagram but also the types of mesophases observed for the monomer and the polymer may be different. 

However, for the majority of the polysoaps studied so far, lyotropic mesophases have not yet been observed. Notably, lyotropic mesophases have rarely been reported for polysoaps of other geometry than tail end type. It may thus be possible that the capability to self-organize into lyotropic liquid crystals is not a general feature of polysoaps, contrasting with standard surfactants. 

There is a second particularity to be noted many virtually water-insoluble polymeric amphiphiles can be swollen to yield polymeric lyotropic mesophases, even if the miscibility gap is broad (Fig. 37). Such behaviour seems to be widespread for vinylic polymerized surfactants with side-chain spacers [126, 231, 331], I.e., neither polysoap behaviour implies the capability to form lyotropic mesophases, nor the presence of lyotropic mesophases the classification as polysoap. 

The cylindrical threads with a great ratio of the length to radius (/ r) form the so-called hexagonal (N) phase. Its sketch is similar to that for the columnar mesophase shown in Fig. 1.8(a). The opposite case is infinite flat lamellae which form the lamellar, smectic A-like (Fig. 1.2(b)) L-mesophase. In between, three nematic lyotropic mesophases are the Nq- 

FIGURE 1.12. (a) Building elements and (b) structinral classification for lyotropic liquid crystals. 

Among lamellar L-phases we can distinguish between liquid-like (a) and solid-like, usually hexagonal (/ ), mesophases which differ from each other in the rigidity of the hydrocarbon tails of amphiphilic molecules. In addition, the tails may, on average, be directed unright (L ,L ) or they may be tilted (Lj, and virtually L ) with respect to the layer normal. This results in different point group symmetry of the L-mesophases [29] and different physical properties. 

A typical compound, which forms a succession of the lyotropic mesophases in water solutions, is the amphiphilic phospholipid lecythine (phosphatidyl choline) 

As compared to the cholesteric LC, the lyotropic LC consists of two or more components that exhibit liquid-crystalline properties (dependent on concentration, temperature, and pressure). In the lyotropic phases, solvent molecules fill the space around the compounds (such as soaps) to provide fluidity to the system. In contrast to thermotropic liquid crystals, these lyotropics have another degree of freedom of concentration that enables them to induce a variety of different phases. A typical lyotropic liquid crystal is surfactant-water-long-chain alcohol. 

A compound that has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule (as mentioned earlier). Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences, depending on the volume balances between the hydrophilic part and the hydrophobic part. These structures are formed through the microphase segregation of two incompatible components on a nanometer scale. Hand soap is an everyday example of a lyotropic liquid crystal (80% soap + 20% water). 

The aggregates created by amphiphiles are usually spherical (as in the case of micelles), but may also be disc-like (bicelles), rodlike, or biaxial (all three micelle axes are distinct) (Zana, 2008). These anisotropic self-assembled nanostructures can then order themselves in much the same way as liquid crystals do, forming large-scale versions of all the thermotropic phases (such as a nematic phase of rod-shaped micelles). 

For some systems, at high concentration, inverse phases are observed. That is, one may generate an inverse hexagonal columnar phase (columns of water encapsulated by amphiphiles), or an inverse micellar phase (a bulk LC sample with spherical water cavities). 

A generic progression of phases, going from low to high amphiphile concentration, is 

1 Ionic Amphiphiles. A variety of ionic amphiphiles, mostly cationic, were 

phases which form along water dilution lines. The simulation of NMR line shapes of unoriented PL bilayers in the L phase and of oriented bilayers in both L and Lp phases was performed through van Faassen s method it was demonstrated that this method, used for dimyristoylPC (DMPC) and dipal-mitoylPC (DPPC) PLs bilayers, involving only numerical integration, is less computationally consuming than other approaches. 

Three pairs of PC-based lipids were designed to cross-link at the termini of 

Several articles deal with the effect of addition of CHOL, protein and peptides to PL bilayers. The interest is justified by the fact the CHOL and some proteins or peptides are natural constituents of biological membranes. Particularly, it 

6 Vesicles, Bicelles and L.C. Dispersions. Vesicles, liposomes, bicelles form as a result of an effective packing parameter v/al 1 of the amphiphilic constituents accompanied by an interplay of different favourable factors. Often, to reach these favourable conditions a mixture of different molecules are needed to combine different conformations of the polar head, different hydration shells, different lengths and conformations (presence of insaturations with different location) of the chain. The result is an arrangement of the bilayer with opposite 

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Lyotropic liquid crystals are discussed in section C2.3 and section C2.6 of tliis encyclopedia and will not be considered furtlier here. 

Lyophobic colloids Lyotropic liquid crystals Lyotropic mesophases Lyotropic polymers Lyral [31906-04-4]... 

Fig. 13. Lyotropic liquid crystal structures (a) micelle formed by a typical soap (b) vesicle formed by a typical phospholipid.

Khoklov, A. R. and Grosberg, A. Yu. Statistical Theory of Polymeric Lyotropic Liquid Crystals. Vol. 41, pp. 53-97. 

Goltner-Spickermann C (2003) Nanocasting of Lyotropic Liquid Crystal Phases for Metals and Ceramics. 226 29-54 Gouzy M-F, see Li G (2002) 218 133-158... 

A compound which displays liquid crystal properties is referred to as a mesogen and said to exhibit mesomorphism. Liquid crystals may be considered either as disordered solids or ordered liquids, and their properties are very dependent on temperature and the presence or absence of solvent. In thermotropic liquid crystals the phases of the liquid crystals may be observed to change as the temperature is increased. In lyotropic liquid crystals the ordered crystalline state is disrupted by the addition of a solvent, which is very commonly water. For these systems temperature changes may also be... 

Figure 2a shows a schematic phase diagram for lyotropic liquid crystals. This figure shows the formation of micelles, cubic phases, bicontinuous cubic phases, and lamellar phases as the concentration of surfactant increases. Also shown in this figure is a schematic diagram of an ordered bicontinuous cubic phase (Fig. 2b). Another interesting example in...

Similar behavior can occur when a crystalline network is disassembled by adding a solvent rather than by heating. These mesogens are called lyotropic liquid crystals and the mesophase formation shows temperature and concentration dependence. They are very important in biological systems, but have been much less studied in materials science. 

Figure 8.4 (a) Atypical molecule that behaves as lyotropic liquid crystal (b) schematic representation of a plate-shaped micelle (c) a spherical micelle (d) a cylindrical micelle. 

The liquid crystal state represents the fourth state of matter and exists between the solid and liquid states, which form its boundaries. The liquid crystal state is reached from the solid state either by the action of temperature (thermotropic liquid crystals) or of solvent (lyotropic liquid crystals) and it is the former that will be the subject of this chapter. 

The role of various surfactant association structures such as micelles and lyotropic liquid crystals (372), adsorption-desorption kinetics at liquid-gas interfaces (373) and interfacial rheology (373) and capillary pressure (374) on foam lamellae stability has been studied. Microvisual studies in model porous media indicate... 

An increase in rod-like arrangement of the macromolecules can also arise by stretching a polymer either in its solid state, either in the melt or even in solution (for polymers leading to lyotropic liquid crystals such as aromatic polyamides). This is the basis of the development of synthetic fibres including high modulus polyethylene Dyneema , polyamide Nylons and Kevlar , polyester Tergal or Dacron fibres. 

Goltner, C. G Henke, S. Weissenberger, M. C. Antonietti, M. 1998. Mesoporous silica from lyotropic liquid crystal polymer templates. Angew. Chem. Int. Ed. 37 613-616. 

Liquid crystal display technology, 15 113 Liquid crystalline cellulose, 5 384-386 cellulose esters, 5 418 Liquid crystalline conducting polymers (LCCPs), 7 523-524 Liquid crystalline compounds, 15 118 central linkages found in, 15 103 Liquid crystalline materials, 15 81-120 applications of, 15 113-117 availability and safety of, 15 118 in biological systems, 15 111-113 blue phases of, 15 96 bond orientational order of, 15 85 columnar phase of, 15 96 lyotropic liquid crystals, 15 98-101 orientational distribution function and order parameter of, 15 82-85 polymer liquid crystals, 15 107-111 polymorphism in, 15 101-102 positional distribution function and order parameter of, 15 85 structure-property relations in,... 

Lyotropic liquid crystals, 15 86, 98-101 amphiphilic molecules in, 25 99-101 Lyotropic mesophases, 20 79 Lyotropic polymer liquid crystals, 25 107-108 Lyral, 2 278 24 486 Lysergic acid, 2 100 Lysergic acid diethylamide (LSD-25),... 

Recent solid state NMR studies of liquid crystalline materials are surveyed. The review deals first with some background information in order to facilitate discussions on various NMR (13C, ll, 21 , I9F etc.) works to be followed. This includes the following spin Hamiltonians, spin relaxation theory, and a survey of recent solid state NMR methods (mainly 13C) for liquid crystals on the one hand, while on the other hand molecular ordering of mesogens and motional models for liquid crystals. NMR studies done since 1997 on both solutes and solvent molecules are discussed. For the latter, thermotropic and lyotropic liquid crystals are included with an emphasis on newly discovered liquid crystalline materials. For the solute studies, both small molecules and weakly ordered biomolecules are briefly surveyed. 

These schemes have been frequently suggested [105-107] as possible mechanisms to achieve the chirally pure starting point for prebiotic molecular evolution toward our present homochiral biopolymers. Demonstrably successftd amplification mechanisms are the spontaneous resolution of enantiomeric mixtures under race-mizing conditions, [509 lattice-controlled solid-state asymmetric reactions, [108] and other autocatalytic processes. [103, 104] Other experimentally successful mechanisms that have been proposed for chirality amplification are those involving kinetic resolutions [109] enantioselective occlusions of enantiomers on opposite crystal faces, [110] and lyotropic liquid crystals. [Ill] These systems are interesting in themselves but are not of direct prebiotic relevance because of their limited scope and the specialized experimental conditions needed for their implementation. 

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