Phase lyotropic

Lyotropic liquid crystalline phases form by water solutions of amphiphilic (particularly biphilic) molecules [11, 12]. The building blocks of those phases are either bilayers, Fig. 4.18, or micelles. The form of the micelles can be spherical or cylindrical. Fig. 4.19a, b. For low concentration of oil in water, the micelles are normal (sketch (a), tails inside, polar heads outside, in water). For high craicentration, the structure is inversed ((b) and (c), water and polar heads inside, tails outside). Examples of the structure of some typical lyotropic phases (lamellar, cubic, hax-agonal) are shown in Fig. 4.20. Under a microscope they show characteristic features. 

There is also a group of the so-called lyotropic nematics. They are intermediate between the isotropic micellar phase and structured (lamellar or hexagonal) phases and can be formed by both discotic and calamitic molecules. The lyotropic nematics can be aligned by an electric or magnetic field and show Schlieren texture as thermotropic nematics. The building blocks of these mesophases are vesicles or similar mesoscopic objects. From the symmetry point of view the nematic phases can be uniaxial or biaxial, as shown in Fig. 4.22. In fact, the biaxial nematics have been found unequivocally only in the lyotropic systems [13]. 

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P. Sakya, J. M. Seddon, V. Vill. Thermotropic and lyotropic phase behavior of monoalkyl glycosides. Liq Cryst 25 409- 24, 1997. 

Liquid crystalline phases1 can be divided into two classes thermotropic phases are obtained by temperature variations and exist in a limited temperature interval (see Figure 7.1) lyotropic phases are instead formed by mixing two or more substances, for example, water and amphiphilic compounds or polymers and a solvent. Especially for amphiphilic compounds in water, temperature may play a role in determining the phase behavior. 

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 very simple model that predicts lyotropic phase transitions is the hard-rod model proposed by Onsager (Friberg, 1976). This theory considers the volume excluded from the center-of-mass of one idealized cylinder as it approaches another. Specifically, if the cylinders are oriented parallel to one another, there is very little volume that is excluded from the center-of-mass of the approaching cylinder (it can come quite close to the other cylinder). If, however, the cylinders are at some angle to one another, then there is a large volume surrounding the cylinder where the... 

Zana R. Dynamics of surfactant self-assemblies micelles, microemulsions, vesicles, and lyotropic phases. New York CRC Press 2005. 

Large numbers of functionalized LB films have been prepared. Highly ordered LB films have been formed by the inclusion of surface-active cobaltous phthalocyanine [168] amphiphilic TCNQ was assembled to function as conducting LB films [169] liquid-crystalline LB films, potentially capable of undergoing thermotropic or lyotropic phase transitions [170, 171], have also been generated. Spacer groups introduced into polymeric surfactants (23) helped to stabilize the LB films which they formed by decoupling the motion of pendant polymers (see Fig. 13) [172]. 

Figure 4. Thermal evolution of the SAXS patterns of the system C12PO4/ water (30/70 w/w). The lamellar lyotropic phase is indexed doot - 9.83 nm (20°C).

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. 

Phase transitions can also take place depending on the concentration of a solvent [37, 38], These lyotropic phases will not be considered here. 

Roux, D. and Safinya, C.R. (1988) A synchrotron X-ray study of competing undulation and electrostatic interlayer interactions in fluid multimembrane lyotropic phases. J. Physique France, 49, 307-318. 

Shearman GC, Ces O, Templer RH et al (2006) Inverse lyotropic phases of lipids and membrane curvature. J Phys Condens Matter 18 S1105-S1124... 

Constantin D, Oswald P (2000) Diffusion coefficients in a lamellar lyotropic phase evidence for defects connecting the surfactant structure. Phys Rev Lett 85(20) 4297-4300... 

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],... 

Zana, R. (ed.), Dynamics of Surfactant Self-Assemblies Micelles, Microemulsions, Vesicles and Lyotropic Phases. CRC New York, 2005. 

LC polymers can either be thermotropic, their LC phases or mesophases are formed by heating a solid or cooling a liquid or solid, or lyotropic, the mesophases are formed by association of molecules in solution. The photochemistry and photophysics of molecules in lyotropic phases such as detergent micelles and lipid bilayers has been a very active research area for about 30 years. This extensive literature [12] is not reviewed in this chapter which is necessarily restricted to thermotropic LC polymers. 

Reaction of various primary amine-terminated dendrimers with either inorganic or organic acids allows the preparation of a wide variety of crystalline derivatives. One such intermediate was implicated in the development of lyotropic phases [156] when octanoic acid was combined with Starburst poly(ethylenimine) (generation-3). 

Initial studies focused on the lyotropic phase behavior of [Ru (bpyla] and [Ru(tpy)2] systems (83,84), but the hrst example of micellization was actually observed in solutions of nonlabile metallosurfactants containing a [Co(polyamine)] center (85). 

Lyotropic Phases. Lyotropic cellulosic mesophases can be observed in a large variety of solvents with derivatives that can be thermotropic (ethylcellulose, hydroxypropylcellulose, acetoxypropylcellulose, etc.) or not (cellulose acetate). 

Pc macrocycle. Some of them are mesomorphic and show a Colh phase (Fig. 79 I-Gl G 115 Coin 270 I II-Gl G <-20 Colh > 320 h H-G2 G 115 Colh 250 I II-G3 94 Colh 108 I) for which the structure of the columnar mesophase is frozen at room temperature (anisotropic glasses). The functionalization of these dendrons in the 3 and 5 position of the terminal rings by oligo(ethyleneoxy) chains (0CH2CH2)30CH3, and their subsequent grafting onto the phthalocyanine of type I (Fig. 79) led to amphiphiUc materials [333]. In concentrated ethanol solutions ( 20-40% by mass), the compound with the fimctionaUzed G1 dendron behaves as a discotic amphiphUe forming a coliunnar nematic lyotropic phase. In addition, it possesses a columnar mesophase stable from room temperature up to 260 °C. Systems of type III are not mesomorphic. 

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