Optical properties of cholesterics

These unique optical properties of cholesteric liquid crystals have been investigated... 

Polymers of cholesteric type attract particular interest among LC polymers — inspired by the unique optical properties of cholesterics 142). 

Arrighi, V., Cowie, J.M.G., Vaqueiro, R, and Prior, K.A., Fine stmcture and optical properties of cholesteric films prepared from cellulose 4-methylphenyl urethane/N-vinyl pynoli-dinone solutions. Macromolecules, 35, 7354, 2002. 

Bobrovsky A, Shibaev V. 2005. Thermo, chiro and photo optical properties of cholesteric azobenzene containing copol5mer in thin films. J Photochem Photobiol A Chem 172(2) 140 145. 

The experimental results presented demonstrate that the optical properties of cholesteric copolymers are determined mainly by the nature of a nematogenic monomer. 

This conclusion is confirmed by the data of Finkelmann and Rehage, who examined the optical properties of cholesteric polysiloxanes. These authors revealed that at equal compositions of copolymers the wavelength of selective reflection depends on the length of the spacer binding nematogenic units. 

We see that the optical properties of cholesterics are quite peculiar. How to explain them on the quantitative basis ... 

The optical properties of cholesteric liquid crystals are very specific and are determined by the pitch and arrangement of the axis of the helix and the polarization of the incident light. In an external field changes occur both in the direction of the axis of the helix (texture transitions) and in its pitch (untwisting of the helix). Before considering these field variations let us give a brief account of the optical properties of cholesteric liquid crystals in the absence of a field. Comprehensive reviews of the topics have been given recently in [1, 2]. 

The optical properties of cholesteric liquid crystals have been studied extensively [23, 24]. Light propagation in helical cholesterics is governed by the spatially periodic relative dielectric tensor, whose eigenvalues are C and i for the electric field parallel and perpendicular to the director n. It can be written as... 

Optical Properties of Cholesteric Liquid-Crystal Films... 

Cholesteric liquid crystals (CLCs) show very distinctly that molecular structure and external fields have a profound effect on cooperative behavior and phase structure (see also Chapters 2 and 3). CLCs possess a supermolecular periodic helical structure due to the chirality of molecules. The spatial periodicity (helical pitch) of cholesterics can be of the same order of magnitude as the wavelength of visible light. If so, a visible Bragg reflection occurs. On the other hand, the helix pitch is very sensitive to the influence of external conditions. A combination of these properties leads to the unique optical properties of cholesterics which are of both scientific and practical interest. 

C. W. Oseen, Arkiv Mat. Astron. Fysik 1928, 21A,l. This paper, like the earlier papers on the continuum theory, is written in German, a language that Oseen stoped using from 1933. References to Oseen s work are nowadays almost uniquely given to his article in English in Trans. Faraday Soc. 1933, 29, 883. While it is true that Eq. (1) is stated there, the article essentially contains the first comprehensive theory of the optical properties of cholesteric liquid crystals. 

Introduction to the Optical Properties of Cholesteric and Chiral Nematic Liquid Crystals... 

A detailed treatment of the optical properties of cholesteric liquid crystals for obliquely incident light beams involves extensive numerical calculations and is outside the scope of this chapter. However, much of the physics underlying the observed optical behavior of these spiral structures can be understood by considering the more restricted case in which the wave vector of the incident light is everywhere normal to the local director, i.e., k 2. The development presented below parallels closely that of de Vries however, the approach is somewhat different. ... 

See, for example, D. W. Berreman and T. J. Scheffer, Reflection and Transmission by Single-Domain Cholesteric Liquid Crystal Films Theory and Verification, Mol. Cryst. and Liquid Cryst, 11, p. 395 (1970) R. Dreher and G. Meier, Optical Properties of Cholesteric Liquid Crystals, Phys. Rev., A8, p. 1616(1973). 

The approach presented in this chapter follows that contained in some unpublished lecture notes of P. S. Pershan on the optical properties of cholesteric liquid crystals. 

Cholesteric mesophases in polymers were limited to these systems alone for a long time. However, due to the greatly increased scientific and practical interest in low-molecular-weight liquid crystals and cholesterics in particular at the end of the 1960s, studies began to be conducted on obtaining new types of thermotropic and lyotropic LC polymer cholesterics. These studies were stimulated by the unique optical properties of cholesterics, which permit widely... 

STRUCTURE AND OPTICAL PROPERTIES OF CHOLESTERIC LIQUID CRYSTALS... 

The features of the optical properties of cholesterics examined above—the high thermal sensitivity of the pitch (and consequently capacity... 

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