Liquid crystal formations

However, the well-depth anisotropy was found to be too large and that k equal to 1/5 does result in liquid crystal formation [16],... 

Both thermotropie and lyotropic liquid crystal polymers exhibit eharacteristic micro-strueture features [9,10]. Anisometrieal monomers such as rods or disks are conneeted to ehains in an appropriate manner. These anisometrieal monomers are considered the mesogens and may be part of main ehain LCP, side chain LCP, or of both types together (Fig. 6). Flexible spacers of nonmesogenic character are located between the mesogens. A sufficient flexibility is a prerequisite for the liquid crystal formation with an increase in temperature or solvent concentration. 

Note 4 The pendant groups in these polymers have structures compatible with liquid-crystal formation, that is, they are mesogenic but not intrinsically mesomorphic. See the examples given in Definitions 2.10 2.11.2.1. 

Table 3 Liquid Crystal Formation in Mixed systems of...

There are a number o-f processes which have not been discussed (because o-f space) in which mixture o-f sur-f actants are important. Among these are foaming, emulsion formation, liquid crystal formation, microemulsion formation, adsorption as 1iquid—1iquid interfaces, and phase partitioning of surfactants between immiscible liquid phases. These areas will also see increased interest in the use of surfactant mixtures. 

As a result of the strong drive to equilibrium, it is usually difficult to quench the isotropic melt to an amorphous glass when liquid crystal formation is possible. Extraordinary quenching techniques may be needed. Once produced, the amorphous state loses its metastability on heating above the glass transition Tga. The melt is quite unstable, so that it may not be possible to keep the melt from changing to the mesophase 21. ... 

In view of the importance of macroscopic structure, further studies of liquid crystal formation seem desirable. Certainly, the rates of liquid crystal nucleation and growth are of interest in some applications—in emulsions and foams, for example, where formation of liquid crystal by nonequilibrium processes is an important stabilizing factor—and in detergency, where liquid crystal formation is one means of dirt removal. As noted previously and as indicated by the work of Tiddy and Wheeler (45), for example, rates of formation and dissolution of liquid crystals can be very slow, with weeks or months required to achieve equilibrium. Work which would clarify when and why phase transformation is fast or slow would be of value. Another topic of possible interest is whether the presence of an interface which orients amphiphilic molecules can affect the rate of liquid crystal formation at, for example, the surfaces of drops in an emulsion. 

However, interest in the process of liquid crystal formation is not... 

While the emphasis of this section has been on kinetics of liquid crystal formation, the rate of liquid crystal dissolution may also be of interest—e.g., in connection with breaking foams and emulsions by adding materials which destroy the liquid crystalline structure. 

Bhargava, R., Wang, S.Q. and Koenig, J. L. (1999) Studying polymer dispersed liquid crystal formation by FTIR spectroscopy 1. monitoring curing reactions. Macromolecules, 32(26), 8982-88. 

When materials susceptible to liquid crystal formation are brought into the proper regime either thermotropically or lyotropically, they will spontaneously form into their characteristic liquid crystalline phase. Blumstein discusses this capability with regard to the formation of microtubules of hemoglobin105. 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

The formation mechanism of this family of materials is determined by two features [45], The first is the dynamics of surfactant molecules to shape molecular assemblies, which leads to micelle, and, ultimately, liquid crystal formation. The second is the capability of the inorganic oxide to undergo condensation reactions to form extended, thermally stable structures. 

Note Evidence for liquid crystal formation for meta- and ortho-phenylnaphthalene monomers was not... 

For the 1 M NaCl system the solubility region was further reduced. Fig. 13, and the water solubilization maximum found at even higher surfactant/cosurfactant ratio. The series with the lower ratios of surfactant to cosurfactant showed an uptake of the aqueous solution somewhat similar to the series in the system with 0.5 M NaCl. The series with the surfactant/(cosurfactant + surfactant) ratio equal to 0.4 gave an initial liquid crystal formation lasting for 2-3 days folllowed by a middle phase lasting a longer time. The liquid crystalline and the middle phase layer were both more pronounced for the sample with initial salt concentration equal in the water and in the microemulsion. Fig. 14A, than for the sample with all the salt in the water. Fig. 14B. 

The diamter of the PBG a-helix has been estimated variously to be between 15-25 A as noted above (25). Values of d used in the determination of persistence len s are listed in the solvent categories of Table I. Values of Vp calculated from Equation 1 using x = L/d are invariably too low for the solvents of this study. Better agreement with the lattice theory has been reported for critical volume fractions of PBG in dimethylformamide and m-cresol (32). Experimental volume fractions for liquid crystal formation of PM in dioxane are lower, however, than those calculated from Flory s theory (33). PBG is known to undergo extensive... 

Intermolecular association in DNF with moisture content and dioxane, making the true aspect ratio of the statistical object in solution these solvents uncertain. If the effective macromolecular length increases due to association, the volume fraction for incipient liquid crystal formation would be expected to be lower. 

Ferrocene derivative 16 showed an enantiotropic nematic phase between 204 °C and 235 °C. This result indicated that a biphenyl system, when associated with the ferrocenyl moiety substituted in the 1,3-positions, was also propitious to liquid crystal formation (compare 16 with its l,T-isomeric analogue 7 (n = 6)). 

There is as yet no clear-cut relationship between the molecular structure of the mesogenic..unit and the type of mesophase it forms, but several generalizations can be made. Gray and Winsor have divided these factors into how the molecular structure (1) is conducive to liquid crystal formation, (2) affects the thermal stability of the mesophase, and (3) favors the occurrence of smectic versus nematic or cholesteric liquid crystals. 

Y. Onogi, T. Hayashi, and M. Yamamoto, Liquid crystal formation control of azobenzene-liquid crystal mixtures by photoisomerization of azobenzene, Nippon Kagaku Kaishi 1990, 250-254. 

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