Ferroelectric liquid crystalline effects

For the small molecular mass ferroelectric liquid crystal when reversing the polarity of the applied electric voltage the molecules rotate locally while their molecular mass centers don t necessarily move accordingly. But for side chain ferroelectric liquid crystalline polymers, as one of the side group ends is confined to backbone, shown in Figure 6.43, the polarity reversion must be accompanied by the movement of their mass centers, which causes a backflow in order to re-distribute the mass centers. Moreover, the side groups may collide with each other. The effect results in the displacement of the backbone. The above effects increase the difficulty of re-orientation and hence increase the viscosity. 

In principle, liquid crystalline polymers can be applied in displays. Unfortunately, the response of them to the external fields isn t satisfactory because their viscosity is greater than the small molecular mass liquid crystals by a few orders of magnitude. In fact, only when the temperature is near the glass transition temperature, can the response be measured in seconds. Apparently, this is far from the real requirement. One may mix the liquid crystalline polymer with small molecular mass liquid crystal for such a purpose, but the mixture doesn t show an advantage over the small molecular mass liquid crystal displays. The ferroelectric liquid crystalline polymer is an exception. It works with a very fast effect and can achieve a display with a response time of a few milliseconds or a fewr tens of milliseconds. 

Lehmaim W, Hartmann L, Kremer F, Stein P, Finkelmann H, Kruth H, Diele S (1999) Direct and inverse electromechanical effect in ferroelectric liquid crystalline elastomers. J Appl Phys 86 1647... 

Yu Y, Maeda T, Mamiya J, Ikeda T. 2007. Photomechanical effects of ferroelectric liquid crystalline elastomers containing azobenzene chromophores. Angew Chem Int Ed Engl 46 881 883. 

Hiraoka K, Toyoda S, Houiai Y, Tokita M, Watanabe J (2010) Influence of DC electric field on soft mode of main-chain ferroelectric liquid-crystalline polyesters polymeric effect on collective fluctuation. Appl Phys Express 3(1). doi 10.1143/APEX.3.011701... 

Liquid crystals are interesting supramolecular systems which can show second harmonic generation when they are aligned appropriately. Ferroelectric LCs [250] as well as bent-core molecules have been used to this purpose, and show reasonable second harmonic generation [251]. These materials combine non-linear optical effects with simple processing procedures on account of their liquid crystalline flow characteristics and the possibility of organising them with electric and magnetic fields. 

Perhaps one of the most important applications of chiral induction is in the area of liquid crystals. Upon addition of a wide range of appropriate chiral compounds, the achiral nematic, smectic C, and discotic phases are converted into the chiral cholesteric (or twisted nematic), the ferroelectric smectic C and the chiral discotic phases. As a first example, we take the induction of chirality in the columns of aromatic chromophores present in some liquid-crystalline polymers. " The polymers, achiral polyesters incorporating triphenylene moieties, display discotic mesophases, which upon doping with chiral electron acceptors based on tetranitro-9-fluorene, form chiral discotic phases in which the chirality is determined by the dopant. These conclusions were reached on the basis of CD spectra in which strong Cotton effects were observed. Interestingly, the chiral dopants were unable to dramatically influence the chiral winding of triphenylene polymers that already incorporated ste-reogenic centers. 

The investigated surfactant/solvent mixtures of the diol C50 and water or for-mamide, respectively, are the first lyotropic systems to form a lamellar, fluid and tilted liquid crystalline phase which contains chiral surfactant molecules. The main issue of the present chapter is thus to demonstrate whether or not the lyotropic SmC analog phase exhibits similar chirality effects as known from its thermotropic counterpart. The most outstanding manifestations of chirality in the thermotropic SmC phase are helicity, due to a chirality-induced precession of the director, and ferroelectricity, due to its polar C2-point group symmetry. Thus, the focus of this chapter is on the detection and analysis of those two macroscopic chirality effects. 

Svensson, M., Helgee, B., Skarp, K., Hermann, D., and Andersson, G., Chiral liquid crystalline side-chain polymers effects of side-chain length on physical properties, Ferroelectrics, 181, 319-326 (1996). 

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.). 

The book is subdivided into three parts. The first three introductory chapters include consideration of the nature of the liquid crystalline state of matter, the physical properties of mesophases related to their electroop-tical behavior, and the surface phenomena determining the quality of liquid crystal cells giving birth to many new effects. The second part (Chapters 5-7) is devoted to various electrooptical effects in nematic, cholesteric, and smectic mesophases including ferroelectric compounds. Here major emphasis is given to explaining the physical nature of the phenomena. The last part (Chapter 8) is a rather technical one. Here recent applications of liquid crystalline materials in electrooptical devices are discussed. 

In this book the authors present a complete and readily understood treatment of virtually all known phenomena occurring in liquid crystals under the influence of an electric field. In the first three chapters (Chapters 1-3) bulk and surface properties of liquid crystalline materials are discussed. The next two chapters (4, 5) are devoted to consideration of the electrooptical effects due to the formation of uniform and spatially modulated structures in nematics. In Chapters 6 and 7 the electrooptical properties of the cholesteric and smectic mesophases are presented, including a discussion of ferroelectric materials. Major emphasis is given to explaining the qualitative aspects of the phenomena and to portraying their physical basis. The prospects for the practical application of electrooptical effects are also discussed (Chapter 8). 

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. 

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