Amphiphilic liquid-crystalline phases

In amphiphilic liquid crystalline phases 4), incompatible molecular parts of flexible molecules cause an LC anisotropy without the presence of a distinct mesogen. The alignment of the junctions between the incompatible parts at interfaces produces the LC structure. 

Amphiphilic liquid-crystalline phases, 233 Anisotropy of mechanical properties, control, 9-10 Aromatic copolyester, 2 Aromatic copolyester analysis using proton NMR spectrometry distribution of correlation times, 256-257... 

Amphiphiles often have a complex phase behaviour with several liquid crystalline phases These liquid crystalline phases are often characterised by long-range order in one directior together with the formation of a layer structure. The molecules may nevertheless be able tc move laterally within the layer and perpendicular to the surface of the layer. Structura information can be obtained using spectroscopic techniques including X-ray and neutror diffraction and NMR. The quadrupolar splitting in the deuterium NMR spectrum can be... 

The ordering of liquid crystalline phases is extensive on the molecular scale. In fact, the self-assembly characteristic as possessed by lipids (amphiphiles) is the basic building feature in LCs. This order extends up to the entire domain size, which may be on the order of micrometers (pm), but usually does not extend to the macroscopic scale as often occurs in classical crystalline solids. However, some techniques (such as the use of boundaries or an applied electric field) can be used to enforce a single ordered domain in a macroscopic LC sample. The ordering in an LC might extend along only one dimension, with the material being essentially disordered in the other two directions. 

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). 

Fig. 43. Hypothetic diagram of liquid crystalline phases formed by amphiphilic molecules in solution 111 Slo, Vlt 2> S2c = cubic phases...

The cubic amphiphilic mesophases (Sic, Vi, and V2) from their interposition in the succession of mesophases Sic, Mi, Vi, G, V2, and M2, have generally been termed liquid crystalline like the optically anisotropic amphiphilic mesophases Mi, G, and M2. The cubic mesophases formed by non-amphiphilic globular molecules have however usually been termed plastic crystals. This nomenclature has obscured the fact that these plastic crystals are fundamentally liquid crystals rather than solid cyrstals and bear a relationship to the optically anisotropic non-amphiphilic smectic and nematic liquid crystals similar to that born by the amphiphilic cubic mesophases to the optically anisotropic neat (G) and middle (Mi and M2) liquid crystalline phases. 

In aqueous solutions of Cm-(EO)n amphiphilic molecules, two interesting features are observed. First, isotropic micellar solutions undergo phase separation on heating. Such behavior is typical of hydrophobic interaction and is also observed for several water-soluble polymers. Hydrophobic interaction results from a change of order in the water structure [54]. Second, at high concentration, liquid crystalline phase behavior is observed with several structures [55]. 

Order and Mobility are two basic principles of mother nature. The two extremes are realized in the perfect order of crystals with their lack of mobility and in the high mobility of liquids and their lack of order. Both properties are combined in liquid crystalline phases based on the selforganization of formanisotropic molecules. Their importance became more and more visible during the last years in Material science they are a basis of new materials, in Life science they are important for many structure associated functions of biological systems. The main contribution of Polymer science to thermotropic and lyotropic liquid crystals as well as to biomembrane models consists in the fact that macromolecules can stabilize organized systems and at the same time retain mobility. The synthesis, structure, properties and phototunctionalization of polymeric amphiphiles in monolayers and multilayers will be discussed. 

The unusual optical properties of liquid crystals had been remarked upon and described for several centuries before their uniqueness as a state of matter was recognised. Their early reports described the strange melting behaviour and appearance of some naturally occurring materials, either as pure compounds or as gels in water, which have now been shown to be thermotropic or lyotropic liquid crystals. Thermotropic liquid crystalline phases are formed under the action of heat, see Figures 2.1 and 2.2, and the lyotropic liquid crystalline phases are formed by the action of a solvent, such as water, usually with an amphiphilic compound. However, the nature of these materials, or indeed their exact... 

The solution behavior of low molecular weight amphiphilic molecules has been intensively investigated in the past (12-16) with respect to the formation of liquid crystalline phases. In very dilute aqueous solutions, the amphiphiles are molecularly dispersed dissolved. Above the critical micelle concentration (CMC), the amphiphiles associate and form micelles (Figure 4) of spherical, cylindrical or disc-like shape. The shape and dimension of the micelles, as a function of concentration and temperature, are determined by the "hydrophilic-hydrophobic" balance of the amphiphilic molecules. The formation of spherical aggregates is preferred with increasing volume fraction of the hydrophilic head group of the amphiphile, because the... 

While only one paper describes the appearance of an anisotropic aqueous solution for a polymer of type D (19), polymers of type A to C have been investigated in more detail recently with respect to formation of liquid crystalline phases (20-23). In the following two sections, the association behavior in dilute isotropic solution and the liquid crystalline phase region is discussed on the basis of some experimental results. The dilute isotropic solutions are of interest with respect to the question whether polymers of type A and B form micelles similar to the corresponding monomeric amphiphiles. The liquid crystalline phase regime gives information whether the linkage of the amphiphiles via a polymer backbone influences the stability of the anisotropic phases and whether the same polymorphism occurs as is known for monomeric amphiphiles. 

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