Mesomorphic ordered systems

The present review is mainly concerned with the preparation and functionalization of micro compositional materials with cellulosic polysaccharides as the principal component, including four major categories graft copolymers, miscible or compatible polymer blends and networks, polysaccharide/inorganic nanohybrids, and mesomorphic ordered systems. Ultrathin layers of cellulosic... 

A new approach to create mesomorphic ordered systems is discussed. Polyacids form H-bonded complexes with tertiary amines and their hydrochlorides having both mesogenic and nonmesogenic structure. 

An even more dramatic example of the potential lack of selectivity afforded to the Norrish II reactions of ketones by supposedly very ordered systems than that described in the 76 systems is provided by neat samples of the mesomorphic alkanophenones (81) [278]. These molecules are capable of existing in nematic and smectic B mesophases (see Figure 16) as shown in Scheme 42. The instability of the monotropic smectic B phase of 81a and smectic B phase of 81b did not allow their photoreactions to be examined these smectic phases became solids soon after the initiation of irradiation. 

Different attempts to lock-in the long-range orientational order of the mesophases of the copper(II) carboxylates have been reported. One of them consisted of replacing the alkanoic acid moiety with a diacetylenic acid, namely, pentacosa-10,12-diynoic acid, to lead to a new mesogenic material which can then be polymerized. The copper complexes formed exhibited a mesophase with a lamello-columnar order, which has been processed into highly ordered crystalline fibers which were polymerized by UV radiation without disruption of the mesomorphic order. The combination of fiber morphology, order, and the presence of oriented polydiacetylene networks suggest that these systems could be of some interest as optically non-linear media. 

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... 

A number of systems which in polymer literature are normally referred to as mesophases are obtained under kinetic control. Examples are the smectic phase of isotactic polypropylene [18,19], mesomorphic syndiotac-tic polypropylene [20-22], mesomorphic PET [23,24], and other instances where intermediate degrees of order result after quenching polymers from the melt to temperatures often close to Tg. In these cases disorder is plausibly more static than in bundles close to T0 and these phases usually crystallize upon heating to an appropriate temperature in the stable crystal phases. 

Heiney and Smith removed the carbonyl groups from Lehn s system 1 by reduction with LiAlH4 in order to find out about the necessity of amide links for the presence of mesophases [109]. Compound 97 (Scheme 47) with amine instead of amide links show no mesomorphism. 

Water and isobutyric acid (IBA) have been chosen as solvents because they form a mesophase with HPC and they have a critical temperature, approximately 26 C for an IBA proportion of approximately 0.4. The phase diagram shows different regions one- or two-phase, mesomorphic, or not. The two-phase region can be segregated. The mesomorphic phase can form a gel or show cholesteric colors (25). The most important Information given by this phase diagram is that the behavior of phase separation of IBA/H2O/HPC system is governed by the extreme preference of HPC for IBA as compared with water. This results in the formation of the ordered phase in dilute HPC solutions as the IBA content in the solvent is reduced. Mesophases can be obtained for low polymer concentrations of a few percent. 

Fulleropyrrolidines constitute an important family of Ceo derivatives that have the advantage over the methanofullerene systems in that they lead to stable reduced species, allowing the development of fullerene-based redox molecular switches. In order to promote mesomorphism in such a mono-adduct structure, Deschenairx et al. decided to modify the Ceo derivative by the use... 

Lipids constitute a diverse and important group of biomolecules. Most lipids can behave as lyotropic liquid crystals. In the presence of water, they self-assemble in a variety of phases with different stmcture and geometry. The lipid polymorphic and mesomorphic behavior, i.e., their ability to form various ordered, crystalline, gel, or liquid-crystalline phases as a function of water content, temperature, and composition, is one of the most intriguing features of lipid-water systems. The mutual transformations between these phases and their physiologic implications are the subject of this article. 

Liquid-crystalline phases are characterized to some degree by the shape of the molecules and by their packing arrangements and ordering in the mesomorphic state. Typically, molecules can have cither disc- or rod-like shapes and can form discotic or calamitic mesophases, respectively. Ferrocene liquid crystal systems that have so far been synthesized tend to have molecular structures that are lath- or rod-like in shape, and consequently the phases observed are calamitic. However, this does not preclude the possibility that a polysubstituted ferrocene could be prepared where the molecular shape is disc-like, thereby holding out the prospect of possibly producing discotic/columnar phases. 

Further studies by Nishiyama et al. [34-45] showed that when taken in isolation, only one of the aromatic units within a supermolecular system has a propensity to exhibit liquid crystal phases, then the supermolecular material itself could be mesomorphic, see Fig. 5. For example, for the top molecular structure, 5 [45], in Fig. 5, only the biphenyl unit at the center of the structure supports mesophase formation, whereas the benzoate units are too isolated from the biphenyl moiety in order to affect mesomorphic behavior. The second material, 6 [45] has terminal phenyl units, which are only connected by aliphatic chains to the benzoate units. Thus in this case, the material has four aromatic units out of six which are not in positions that can enhance mesophase formation. However, the second material has similar transition temperatures and phase sequences to the first, i.e., both materials exhibit an unidentified smectic phase and a synclinic ferroelectric smectic C phase. If the third material, 7 [38], is examined, it can be seen that the mesogenic unit at the center of the supermolecule is an azobenzene unit which is more strongly supportive of mesophase behavior than the simple biphenyl moiety. Thus the clearing point is higher for this material in comparison to the other two. The attachment of the terminal phenyl unit is by a methylene spacer of odd parity, and as a consequence the smectic C phase has an anticlinic structure rather than synclinic. 

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