Ferroelectric liquid crystalline

In this section, we will present the crystal structures of chiral mesogenic compounds exhibiting ferroelectric liquid crystalline phases which are listed in Table 18 [152-166]. Moreover, four compounds of the list show antiferroelectric properties and two compounds form only orthogonal smectic phases. The general chemical structures of the investigated chiral compounds are shown in Fig. 27. 

Ferroelectric liquid crystalline monomers (Fig. 21, XXXVII) bearing two terminal vinyl groups were polymerized directly from their smectic A" liquid crystal phase using a Grubbs-type initiator. 

Miyazawa, K., Yulil, D. S., Howard, J. A. K. and de Meijere, A. (2000) Cyclopropyl building blocks fororganic synthesis, 60. Synthesis and properties of optically activedispiro[2.0.2.1 ]heptane derivatives as novel ferroelectric liquid crystalline compounds. Eur. J. Org. Chem., 2000, 4109-4117. 

The photoinduced flop of the polarization of ferroelectric liquid crystals showing a quick response was achieved by dissolving azobenzene moieties in the liquid crystals.114,11 Photocontrol of the switching behavior of ferroelectric liquid-crystalline polymers (33, Figure 14) was induced by admixing azobenzene derivatives.116... 

Figure 2.52 Ferroelectric liquid-crystalline chiral /3-diketonate complexes (M = VO,...

It is difficult to grow a good organic crystal film and a Langimur-Blogette film of up to 1 micron thickness. However, polymers have a wide choice and can be tailored to meet the above requirements. The polymers may be side chain liquid crystalline polymers, ferroelectric liquid crystalline polymers and amorphous polymers. Among them the side chain liquid crystalline polymers have drawn more attention. 

The backbone affects the dynamic behavior of the ferroelectric liquid crystalline polymer. Sandwiching the two kinds of ferroelectric liquid crystals between two ITO-coated glass plates of 1.5 microns gap respectively, one constructs a SSFLC (surface stabilized ferroelectric liquid crystal) cell. The switch time between two optical states r is determined by... 

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. 

Endo et al. (1992) measured the optical transmission and the polarity-reverse current during the polarity reversion of a side chain ferroelectric liquid crystalline polymer. It was found that both parameters reached peak values at the same time. It was concluded that the rigid core of the side groups responsible for birefringence moves simultaneously with the dipole moment reversion and the latter contributes to the polarity reversion current. The FTIR experiment suggested that the backbone moves when the polarity is reversed. 

The molecule contains Si-0 bonds. FTIR suggested that the Si-0 bonds move when the side groups move. Hence, ferroelectric liquid crystalline polymers have higher rotational viscosities than small molecular mass ferroelectric liquid crystals. In Figure 6.44 the relation of rotational viscosity r/ and molecular weight Mw at 600 °C is plotted, rj increases as Mw increases and the quadratic law is observed. 

Scherwsky et al. (1989) first utilized a SSFLC display in terms of the ferroelectric liquid crystalline polymer. The polymer SSFLC display is fabricated on the ITO-coated plastic substrate. The display was 15 x 40 cm2 in area and had 100 x 300 pixels (Lagerwell, 1993). The display doesn t need the orientation layer which is essential in the conventional liquid crystal displays in order to anchor the liquid crystal molecules. By lightly bending the... 

If some of the side groups are substituted by dyes or fluorescent molecules, the display may work without polarizers. It is expected that large screen ferroelectric liquid crystalline polymer displays will come out in the near future. 

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... 

Leister N, Lehmann W, Weber U, Geschke D, Kremer F, Stein P, Fiiikelmann H (2000) Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of single crystalline ferroelectric liquid crystalline elastomers. Liq Cryst 27 289... 

Skupin H, Kremer F, Shilov SV, Stein P, Finkelmann H (1999) Time-resolved FTIR spectroscopy on structure and mobility of single crystal ferroelectric liquid crystalline elastomers. Macromolecules 32 3746... 

Ferroelectric liquid crystals (FLC) are of great interest due to their fast electro-optical response which is about 1,000 times faster than conventional twisted nematic cells [131]. The geometry used is called a surface stabilized FLC cell which utilizes a very thin gap (=2 pm) to unwind the FLC supramolecular pitch (=1-2 pm) since the bulk FLC materials do not show macroscopic polarization. This very thin gap, however, leads to difficulties in manufacturing large panels and very poor shock resistance. Researchers have proposed the concept of microphase stabilized FLC [79,109, 130] using FLC-coil diblock copolymers for electro-optical applications as shown in Fig. 15. This concept takes advantage of ferroelectric liquid crystallinity and block copolymer microphase separation since the block... 

Brehmer M, Zentel R. 1994. Ferroelectric liquid crystalline elastomers. Macromol Chem Phys 195 1891 1904. 

Brodowsky HM, Boehnke UC, Kremer F, Gebhard E, Zentel R. 1999. Mechanical deformation behavior in highly anisotropic elastomers made from ferroelectric liquid crystalline polymers. Langmuir 15 274 278. 

Lehmann W, Skupin H, Tolksdorf C, Gebhard E, Zentel R, Kruger P, Losche M, Kremer F. 2001. Giant lateral electrostriction in ferroelectric liquid crystalline elastomers. Nature 410 447 450. 

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. 

Ferroelectric Liquid Crystalline Poly(meta-phenylene)... 

We synthesized a ferroelectric liquid crystalline PMP by incorporating a fluorine-containing chiral LC group into the side chain [14]. Figure 11.17 shows the structure of the FLC-PMP, Poly-8, M = 4,200) bearing a chiral FLC side chain and the FLC molecule a fluorine-containing triphenyl compound, FTP. 

In addition to investigating ferroelectric liquid crystalline conjugated polymers with dynamic switching functionahties under an electric field, our group has also developed photoresponsive liquid crystalline conjugated polymers with dynamic switching of linearly and circularly polarized luminescence. This was accomplished through the use of a photoisomerizable moiety in the polymer side chain. 

K. Suda, K. Akagi, Electro-optical behavior of ferroelectric liquid crystalline polyphenylene derivatives. J. Polym. Sci. Part A Polym. Chem. 46, 3591-3610 (2008)... 

M. Mitsuishi, S. Ito, M. Yamamoto, H. Endo, S. Hachiya, T. Fischer, W. Knoll, Optical characterization of a ferroelectric liquid crystalline polymer studied by time-resolved optical waveguide spectroscopy. Macromolecules 31, 1565-1574 (1998)... 

H. Goto, X. Dai, H. Narihiro, K. Akagi, Synthesis of polythiophene derivatives bearing ferroelectric liquid crystalline substituents. Macromolecules 37, 2353-2362 (2004)... 

Time-resolved FTIR is used to study the structure and dynamics of ferroelectric liquid crystalline block copolymers. From analysis of the dynamic dichroism of the FTIR spectra, it was concluded that the components in the PS microphase are oriented randomly while the liquid aystalline groups form an ordered phase. The switching is of an electroclinic type, in which the tilt angle and the mesogenic motion increase with temperature, especially if the PS block is heated above Tg. The orientation of the liquid crystalline block after... 

Recently, liquid-crystalline polyphenylene derivatives have been synthesized through substitution of a fluorine-containing chiral liquid-crystalline group into side chains, with an aim to develop ferroelectric liquid-crystalline conjugated polymers (Fig. 5 Suda and Akagi 2008). These are attracting interest because they can afford anisotropies in electrical and optical properties when they are macroscopically aligned. This study also elucidated that PPP can be used to prepare new types of polymer materials. 

Mesogenic groups can be incorporated into polymeric systems [7]. This results in materials of novel features like main chain systems of extraordinary impact strength, side-chain systems with mesogens which can be switched in their orientation by external electric fields or—if chiral groups are attached to the mesogenic units—ferroelectric liquid crystalline polymers and elastomers. The dynamics of such systems depends in detail on its molecular architecture, i.e. especially the main chain polymer and its stiffness, the spacer molecules... 

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