Ferroelectric liquid crystals optical properties

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

Liquid crystals have found widespread application in optical display devices as well as in detection of temperature uniformity and impurities. These properties are related to the orientational order of molecules in the temperature region between and the melting point. The possible applications of ferroelectric liquid crystals are promising. Superconductors (type II) can be used to create high magnetic fields at low power the ability of type I superconductors to trap magnetic flux within the domains of the normal material may also have applications. 

Obviously, chirality is an essential property in molecular chemistry, and knots are exciting systems in this context. With a touch of fantasy, it could be conceived that some of the chemical processes for which chirality is essential (enan-tioselection of substrates, asymmetric induction and catalysis, cholesteric phases, and ferroelectric liquid crystals molecular materials for non linear optics...) could one day use enantiomerically pure knots. 

Haase and co-workers investigated electro-optic and dielectric properties of ferroelectric liquid crystals doped with chiral CNTs [495, 496]. The performance of the doped liquid crystal mixture was greatly affected even by a small concentration of CNTs. The experimental results were explained by two effects (1) the spontaneous polarization of the ferroelectric liquid crystal is screened by the 7t-electron system of the CNT and (2) the CNT 7i-electrons trap ionic impurities, resulting in a significant modification of the internal electric field within liquid crystal test cells. 

More modern, much faster responding liquid crystalline displays use ferroelectric liquid crystals such as p decyloxybenzylidine-//-amine-2-methylbulylcinnamale, which can be switched between two stable states by application of an external field. Such properties may also be useful in optical data storage. 

Cross-linked polymeric liquid crystals offer a wide variety of unique and in-tere.sting properties. Because of the interaction between the mesogens and the network backbone in liquid crystal elastomers, mechanical deformations can align the director, and these materials are piezoelectric. Industrial applications of liquid crystalline thermosets are driven by additional properties such as toughness, a tunable coefficient of thermal expansion, ferroelectricity, and nonlinear optical properties. Reviews on this topic are given by Barclay and Ober [4] and by Warner and Terentjev [5]. 

Like solid ferroelectrics, the ferroelectric liquid crystals, particularly the FLCPs, show a pyroelectric effect and a piezoelectric effect and are capable of switching polarization direction (dielectric hysteresis). Moreover, they can switch propagating or reflected polarized light. Finally, the polar symmetry of the phase leads to nonlinear optical properties of the FLCPs such as second-harmonic generation, the Pockels effect, and the Kerr effect. These physical properties of the ferroelectric LC polymers are discussed in the following sections. 

Zentel, R., Poths, H., Kremer, F., Schdnfeld, A., Jungbauer, D., Twieg, R., Willson, C. G., and Yoon, D., Polymeric liquid crystals structural basis for ferroelectric and nonlinear optical properties, Polym. Adv. Technol., 3, 211-217 (1992). 

The surface-stabilized ferroelectric liquid crystals in the smectic C (SmC ) phase are among the most interesting types of liquid-crystalline systems because of their potential applications in high-resolution flat panel displays and fast electro-optical devices [73-76]. Within this class of compounds, ferroelectric liquid-crystalline polymers (FLCPs) have gained theoretical and practical interest as systems which combine the properties of polymers and ferroelectric liquid crystals. This combination is achieved by attaching the ferroelectric mesogen to a main chain via a flexible spacer... 

As pointed out already in Section 2.5.5, low-molecular weight ferroelectric liquid crystals (FLCs) and FLCPs are attracting a lot of interest because of their potential for electro-optical applications. The polymers offer new possibilities, e.g., as elastomers for piezoelectric elements or by copolymerization [77, 78, 105] due to the formation of intrinsic mixtures between SmC mesogenic units and other comonomers. This leads to FLCPs combining several material properties which might be utilized for colored displays in the case of comonomers containing chromophores. For the differentiated evaluation of such copolymers with reference to the possible exploitation of nonlinear optical (NLO) properties, the interplay of the different orientation tendencies of the side-chain functionalities is of crucial importance [36,106]. 

This book was conceived as a renewed version of the earlier published original book, Electro-Optical and Magneto-Optical Properties of Liquid Crystals (Wiley, Chichester, 1983) written by one of us (L.M. Blinov). That book was first published in Russian (Nauka, Moscow, 1978) and then was modified slightly for the English translation. Since then new information on electrooptical effects in liquid crystals has been published. Novel effects have been discovered in nematics and cholesterics (such as the supertwist effect), and new classes of liquid crystalline materials, such as ferroelectric liquid crystals, appear. Recently, polymer liquid crystals attracted much attention and new electrooptical effects, both in pure polymer mesophases and polymer dispersed liquid crystals, were studied. An important contribution was also made in the understanding of surface properties and related phenomena (surface anchoring and bistability, flexoelectricity, etc.). 

Ferroelectric liquid crystals (FLC) have attracted attention because of their high speed response and memory effect (7-5). The characteristics of fast response and memory effect make them suitable in electro-optical device applications, such as display, light valve and memory devices. Ferroelectric side chain liquid crystalline polymers (FLCPs) exhibit desirable mechanical properties of polymers and electro-optical properties of low molecular weight FLC, which have been investigated extensively Corresponding author. 

The present chapter is devoted to a discussion of electric field effects in various liquid crystal phases, with an emphasis on the physical aspects of the phenomena. The discussion is based on classical results, although the most important recent achievements in the field are also mentioned. As ferroelectric liquid crystals are covered in detail in other chapters in this book, they are discussed only briefly here for the sake of completeness. Electro-optical properties of... 

The exciting ferroelectric and electro-optical properties of bent-core liquid crystals will be also discussed in Chapter 8. 

Archer P, Dierking I (2009) Electro-optic properties of polymer-stabilized ferroelectric liquid crystals before, during and after photo-polymerization. J Opt A Pure Appl Opt 11(2) 024022 Archer P, Dierking I, Osipov MA (2008) Landau model for polymer-stabilized ferroelectric liquid crystals experiment and theory. Phys Rev E 78(5) 051703 Bahr CH, Heppke G (1990) Influence of electric field on a first-order smectic-A-foroelectric-smectic-C liquid-crystal phase transition a field-induced critical point. Phys Rev A 41 (8) 4335 342... 

Lahiri T, Pal Majumder T (2012) The effect of cross-linked chains of polymer network on the memory states of polymer stabilized ferroelectric molecules. Polymer 53 2121-2127 Lee K, Suh SW, Lee SD (1994a) Fast linear electro-optical switching properties of polymer-dispersed ferroelectric liquid crystals. Appl Phys Lett 64 718 Lee K, Suh SW, Lee SD, Kim CY (1994b) Ferroelectric response of polymer-dispersed chiral smectic C liquid crystal composites. J Korean Phys Soc 27(1) 86... 

Suresh S, Chien LC (2003) Electro-optical properties of polymer-stabilized ferroelectric liquid crystal. Ferroelectrics 287 1-6... 

Rudzki A, Evans DR, Cook G, Haase W (2013) Size dependence of harvested BaTi03 nanoparticles on the electro-optic and dielectric properties of ferroelectric liquid crystal... 

XL13654, and SCE9. A well-studied ferroelectric liquid crystal is DOBAMBC its molecular structure is shown in Figure 4.1 Ic. Because of these differences in the degree of order and molecular arrangement and the presence of a permanent dipole moment, the physical properties of smectic liquid crystals are quite different from those of the nematic phase. In this and the following sections we examine the pertinent physical theories and the optical properties of three exemplary types of smectics smectic-A, smec-tic-C, and (ferroelectric) smectic-C. ... 

Experimentally, Tca Tc a and rclA found to be veiy close to one another. This is expected as the chital terms in the fiee-eneigy expression are basically small-peituibation terms. Their optical and electro-optical properties, however, are considerably modified by the presence of the chirality and spontaneous polarizatioir As we remarked earlier, ferroelectric liquid crystals provide a faster electro-optical switching mechanism. In the corrtext of nonlinear optics, the noncerrtrosyrrrmetry carrsed by the presence of P allows the generation of even harmorric light. 

Extensive research has already been carried out on incorporation of fluorine into molecules which can lead to profound and unexpected results on biological activities and/or physical properties [ 1 - 5]. In particular, optically active fluorine-containing molecules have been recognized as a relatively important class of materials because of their interesting characteristics and potential applicability to optical devices such as ferroelectric or antiferroelectric liquid crystals [6-11]. Recent investigations in this field have opened up the possibility for the... 

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