Ferroelectric liquid crystalline polymers

By appropriately installing two polarizers on two surfaces of the cell the bright/dark states can be obtained by changing the polarity of the applied voltage. The response of the liquid crystal cells is much faster than other liquid crystal displays. The response time is inversely proportional to the spontaneous polarization Ps and applied electric held E, and is linear in proportion to viscous coefficient 77. It is typically tens of microseconds. In comparison, the relaxation time is generally tens of milliseconds for other liquid crystal displays. The ferroelectric liquid crystal display exhibits the 

In the last few years the anti-ferroelectric liquid crystal Sca was discovered by Chandani et al. (1988, 1989) in MHPOBC 

Compared with conventional ferroelectric liquid crystals, anti-ferroelectric liquid crystals have the following advantages  

Assume a side chain liquid crystal polymer, consisting of a flexible backbone and mesogenic side groups, is able to form the Sc phase and its glass transition is below the ambient temperature, such a side chain liquid crystal polymer will be expected to show ferroelectricity. The side groups are packed in a way similar to small molecular mass ferroelectric liquid crystals. The backbone is suppressed between layers, occasionally penetrating into them. The conformation of the backbone is discus-like. 

Introduce the chiral center into one end of the side groups and one may obtain a cholesteric liquid crystalline polymer. If both mesogenic units 

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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... 

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. 

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. 

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)... 

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... 

Shilov, S. V. Okretic, S. Siesler, H. W. Zentel, R. Oge, T., Fourier-Transform Infrared Study of the Switching Process in a Ferroelectric Liquid Crystalline Polymer. Macromol. Rapid Commun. 1995,16,125-130. 

These modes can also be observed in ferroelectric liquid crystalline polymers (FLCPs). The soft mode is connected with the change of the molecular tilt angle 0 near the phase transition from an untilted to a tilted phase (e.g., Sm A /Sm C ). For low-molar-mass compounds it usually has a frequency of 10 to 10 Hz. For... 

Kozlovsky, M. V., and Bere.snev, L. A., Ferroelectric liquid crystalline polymers, Phase Transitions, 40, 129-169 (1992). 

Kiefer, R., Application of ferroelectric liquid crystalline polymers, in Ferroelectric Polymers Chemistry, Physics, and Applications (H. S. Nalwa, ed.), Marcel Dekker, New York, 1995, pp. 815-880. 

KUhnpast, K., Springer, J., Davidson, P, and Scherowsky, G., Spacer length and molecular weight variation on ferroelectric liquid-crystalline polymers. Makromol. Chem., 193, 3097-115 (1992). 

Hsu, C.-S., and Hsiuc, G.-H., Molecular design of ferroelectric liquid crystalline polymers, Pure Appl. Chem., 67, 2005-2013 (1995). 

Scherowsky, G., Fast-switching ferroelectric liquid-crystalline polymers. Mol. Cryst. Liq. Cry.st., 69, 87-98 (1993). 

Kawasaki, K., Kidera, H., Sekiya, T, and Hachiya, S., Molecular motion of ferroelectric liquid crystalline polymers, Ferroelectrics, 148, 233-243 (1993). 

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