Chiral nematic mesophase

Mixtures of a nematic liquid crystal (LC or LC ) with small quantities of gold nanoparticles coated with alkylthiolates (<5 wt%) including an alkylthiolate functionalized with a chiral group have been studied (Figure 8.29) [72]. All mixtures show nematic mesophases with transition temperatures and phase stability very similar to those oftheliquid crystal precursors LC or LC. The introduction ofachiral center into the mixtures (mixtures of Au ) produce chiral nematic mesophases. A similar result is obtained in mixtures of Au and LC doped with the chiral dopant (s)-Naproxen. 

See Fig. 3 for an illustration of the helicoidal molecular distribution in a chiral nematic mesophase. 

Note 1 Locally, a chiral nematic mesophase is similar to a uniaxial nematic, except for the precession of the director n about the axis, Z. 

Note 3 Chiral nematic mesophases exhibit Bragg scattering of circularly polarised light at a wavelength proportional to the pitch P (Xr = P, where is the mean refractive index). 

Note 4 The director precession in a chiral nematic mesophase is spontaneous and should be distinguished from an induced twisted structure produced by a mechanical twist of a nematic mesophase between confining surfaces. 

Note 5 The term chiral nematic mesophase or chiral nematic is preferred to cholesteric mesophase or cholesteric. 

Note 3 With chiral nematic substances forming chiral nematic mesophases of short pitch (<700 nm), up to three blue phases occur in a narrow temperature range between the chiral nematic phase and the isotropic phase. 

Note 3 Two TGBA structures are possible in one, the number of blocks corresponding to a rotation of the layer normal by 2ti is an integer, while in the other, it is a non-integer. Note 4 A TGBA is found in a phase diagram between smectic A and chiral nematic mesophases or between a smectic A mesophase and an isotropic phase. 

Fig. 2 Fingerprint pattern for chiral nematic mesophase of 40% EC in m-cresol. (View this art in color at www.dekker.com.)...

Besides degree of substitution, nature of substituents, solvent, concentration, and temperature, other factors that change the polymer-solvent interactions can affect the pitch of lyotropic cellulosic mesophases. Doping inorganic salts " or small chiral molecules into the lyotropic mesophase changes the polymer-solvent interactions. As the results, the pitch of the chiral nematic mesophase changes accordingly. 

Gray, D.G. Harkness, B.R. Chiral nematic mesophase of lyotropic and thermotropic cellulose derivatives. In Liquid Crystalline and... 

Harkness, B.R. Gray, D.G. Left- and right-handed chiral nematic mesophase of (trityl) (alkyl)cellulose derivatives. Can. J. Chem. 1990, 68 (7), 1135-1139. 

Many of the compounds used as examples in this chapter to illustrate the three classes of chiral nematic structure are not necessarily compounds in which the presence of a chiral nematic phase or its properties were of primary importance to the researchers concerned in the work for instance some of the materials were developed as potential ferroelectric dopants, but happened to show a chiral nematic mesophase. Also in many cases, the synthetic techniques used and the hazardous nature of some of the reagents employed, along with the poor chemical or photochemical stabilities of the mesogens, would almost automatically preclude their use in any commercial applications (i.e., thermography). However, such materials are of scientific interest in that they help to illustrate the many potential variations of novel molecular structures which may result in a chiral nematic mesophase. 

The introduction of a third ring to give materials such as compound 30, led to markedly higher thermal stabilities. This compound is reported as having an optical rotation of 25 000 degrees mm in its chiral nematic phase, further highlighting the extraordinary optical properties associated with the chiral nematic mesophase. 

Cholesteric mesophases A sub unit of the nematic mesophases is the Cholesteric mesophases or chiral nematic mesophases. It is nematic because each plain of polymer chains has got a nematic director, but has the additional features that... 

Induced chiral nematic mesophase mixed with a bifunctional UV-curable monomta- Imprinted ilexibie photonic cell Chien and Liu (2014)... 

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