Mesomorphic behavior

Bulky, even if highly polari2able, functional groups or atoms that are attached anywhere but on the end of a rod-shaped molecule usually are less favorable for Hquid crystal formation. Enhanced intermolecular attractions are more than countered as the molecule deviates from the required linearity. For example, the inclusion of the bromine atom at position three of 4-decyloxy-3-bromoben2oic acid [5519-23-3] (9) prevents mesomorphic behavior. In other cases the Hquid crystal phases do not disappear, but their ranges are narrower. 

In summary, [Au(alkynyl)(CNR)j complexes also show mesomorphic behavior but, in contrast to the halide-isocyanide derivatives, they are thermally less stable and usually decompose before or at the clearing temperatures. This thermal instability is thought to be associated with the gold-(alkynyl) bond and makes these compounds... 

Mesitylene, production from acetone, 1 164 Mesityl oxide, 14 589-590 characteristics of, 16 337 hydrogenation, 16 337-338 hydrogen peroxide treatment of, 16 338 Z-menthol from, 24 520 production of, 16 336-337 production from acetone, 1 164, 174 Mesogenic diols, 25 460 Mesogenic molecules, solids of, 15 82 Mesogens, 24 53, 54 Mesomixing, 16 683 Mesomorphic behavior, 24 53-54 Mesomorphic phase transitions, 15 102 Mesomorphism, 15 81. See also Liquid crystalline materials Mesophase pitch-based carbon fiber, 26 734-735... 

Although numerous amphiphilic monomers have been polymerized and a great number of amphiphilic polymers have been investigated, only some hints in the literature indicate mesomorphic behavior of concentrated polymer solutions 105.106.121>. Nearly all measurements were carried out "at low concentrations, in order to characterize the properties of these polysoaps in view of applications as surfactants. For these applications high polymer concentrations are, of course, not of interest. 

Most interesting are the effects of salt complexation on the mesomorphic behavior of liquid crystalline crown ethers and liquid crystalline crown ether polymers. Sodium triflate was added to poly(17) [34] and poly(25) (Scheme 14) [39]. The enantiotropic nematic and smectic phases of poly(17) were changed dramatically [40]. With increasing amounts of salt, the clearing temperatures are shifted to higher values while the melting transition increases only slightly. 

Ringsdorf investigated the complexation of Co(N03)2, NifNOib. and Cu(N03)2 on the mesomorphic behavior of amine-linked 98 and 99 [112] (Scheme 48). Complexation induced mesomorphism in both substrates (Table 7). 

Fig. 15 Mesomorphic behavior of 108, 111 and their metal complexes white shade crystalline, grey shade columnar hexagonal ordered, black shade columnar, - plastic...

When the lateral substituents were changed from ether to gallic ester groups, a columnar hexagonal phase was observed for 112, while complexation with KI destroyed the mesomorphic behavior [121] (Scheme 58). The presence of ion pairs in the complex presumably leads to unfavorable interactions between neighboring molecules leading to non-mesogenity. 

Some polysiloxanes form liquid-crystalline phases because of the presence of relatively stiff side chains.168-176 They have been much studied, particularly with regard to the effect of deformation of the elastomeric polysiloxane phase on the mesomorphic behavior exhibited by the side chains. 

Quite recently, a series of N-alkyl substituted imidazolium salts has been evaluated for additive effects on the mesomorphic behavior and ensuing optical properties of HPC aqueous solutions, followed by characterization of the thermotropicity of novel cellulose derivatives with such an ionic liquid structure in the side-chains [193]. 

In this chapter we have described the mesomorphic behavior and ionic conductivities of ionic liquid-based liquid crystalline materials. These ion-active anisotropic materials have great potentials for applications not only as electrolytes that anisotropically transport ions at the nanometer scale but also as ordered solvents for reactions. Ionic liquid crystals have also been studied for uses as diverse as nonliner optoelectronic materials [61, 62], photoluminescent materials [78], structuredirecting reagents for mesoporous materials [79, 80] and ordered solvents for organic reactions [47, 81]. Approaches to self-organization of ionic liquids may open a new avenue in the field of material science and supramolecular chemistry. 

Table 1 Mesomorphic behavior of the monodendrons based on the AB3 building block methyl 3,4,5-trishydroxybenzoate (X = C02Me, CO2H, CH2OH R = OC12H25) ...

Table 4 Mesomorphic behavior of the carbosilane dendrimers bearing cyanobiphenyl mesogens ...

Table 5 Mesomorphic behavior of the isomeric carbosilane dendrimers bearing methoxyphenyl benzoate (B) and anisic acid derivative (D) mesogens...

Note that this behavior is in marked contrast to that of the zeroth to the second generation of related PAMAM and PPI dendrimers (Nc = 3, Mb = 2) with 4 -cyanobiphenyl hydrogen glutarate that did not produce any mesomorphic behavior, except a lyotropic nematic phase in 80 wt % N,N -dimethylformamide (DMF) solutions containing lithium bromide [204,205]. 

In order fo furfher invesfigafe fhe influence of fhe sfrucfure of the mesogenic units on the mesomorphic behavior of the dendrimers, bulky units have been introduced at the periphery of the third and fourth generations of amino-terminated PAMAM and PPI (Fig. 39, L3, Le, L9), wifh the aim of achieving cubic mesophases, since the increased volume around the dendritic core could in principle force the dendrimer to adopt a globular conformation [199,222],... 

A theoretical approach to identify the key topological and statistical ingredients for the description of the self-organization and of the mesomorphic behavior of such dendritic supermolecules has been developed [224-226]. 

Table 9 Mesomorphic behavior of the dendrimers bearing bent-mesogens...

Table 12 Mesomorphic behavior of the dendrimers with a polyester core ...

Table 13 drimers) Mesomorphic behavior of the wUlow-like dendrimers (dendrons and den-... 

Fig. 67 Mesomorphic behavior of the malonate and corresponding methanofuiieroden-drimers...

Table 17 Mesomorphic behavior of the tetrameric polypedes and multipedes...

Another example of a rigid macrocycle used as the central core of a den-drimer is the porphyrin. First and second generation phenylene-based dendritic porphyrins with 8 and 16 long alkyl chains on their periphery have been studied (Fig. 80). Only the second generation exhibits mesomorphic behavior with the formation of a rectangular columnar mesophase upon heating (Cr 39 Coir 110 I) [334]. A stable supramolecular 1 1 complex was formed between the second generation and Ceo, which led to the enhancement of the mesophase stabiUty of the formed (imidentified) columnar phase (Cr 99 Col 250 I). 

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. 

Interesting liquid crystal properties resulted from the Schiff-base derivatives 11 [18]. All compounds exhibited mesomorphic behavior (Fig. 9-6). The first members of the series gave rise to enantiotropic nematic phases and the long chain derivatives exhibited enantiotropic smectic A phases. The intermediate chain length derivatives presented monotropic nematic or smectic A phases. 

No mesomorphic behavior resulted from family 17 [22] (Fig. 9-12). This observation is of interest, as it showed that a limit exists for obtaining liquid crystallinity even in the case of 1,3-disubstituted ferrocene derivatives. 

Threshold volume fractions observed for cellulose acetate (CA and CTA), ethyl cellulose (EC) and hydroxypropyl cellulose (HPC), each in various solvents, are presented in Table 3. The results depend to some extent on the solventThe data included are not exhaustive. Other cellulose esters exhibit mesomorphic behavior Chanzy et al. observed mesomorphic behavior in solutions of cellulose itself when dissolved in N-methylmorpholine N-oxide containing water at concentrations of cellulose in the range 20-55 % w/v, depending on the temperature, the water content of the solvent and the degree of polymerization of the cellulose. Solutions of cellulose in mixtures of trifluoroacetic acid with 1,2-dichloroethane or with chloroform are hkewise lyotropic at concentrations of 20% (w/v) and above according to Patel and Gilbert... 

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