Polymer liquid crystals smectic phases

The systematic synthesis of non amphiphilic l.c.-side chain polymers and detailed physico-chemical investigations are discussed. The phase behavior and structure ofnematic, cholesteric and smectic polymers are described. Their optical properties and the state of order of cholesteric and nematic polymers are analysed in comparison to conventional low molar mass liquid crystals. The phase transition into the glassy state and optical characterization of the anisotropic glasses having liquid crystalline structures are examined. 

Kilian, D., Kozlovsky, M. V., and Haase, W. Dielectric measurements on the isotropic smectic phase of dyed side-chain polymers. Liquid Crystals 26, 705 (1999). 

In (3.67), n = 7-12. The polymers have a smectic phase. The temperatures of the transitions from crystal to smectic phase (Tcs) and from smectic to isotropic liquid (Tsi) are shown in Table 3.17. The structure of... 

The interaction of carboxylic acids affects the molecular order of side-chain polymer liquid crystals [130]. Copolymerization of an acrylate containing a cyanobiphenyl unit through butyl group and acrylic acid leads to the induction of a smectic A phase. The intra- and intermolecular H-bonds of carboxylic groups stabilize layered structures. 

FIGURE 5.3 Schematic representation of (a) nematic phase and (b) smectic phase for main-chain liquid crystalline polymers, showing the director as the arrow. The relative ordering is the same for side-chain-polymer liquid crystals. 

The optical microscopy of these polymer liquid crystals identifies both polymers as having smectic A phases only. However unlike monomer materials the evolution of a particular well defined texture may take several hours. As is shown in plates l(a-c) the smectic fan texture can be seen to grow gradually over 15 hours on annealing just below All of the photomicrographs are for PG296 which... 

In this chapter we shall only be concerned with electro-optic and thermo-optic switching effects in thermotropic side-chain polymer liquid crystals. We will consider briefly the synthesis and structure of such compounds and show how the nematic, cholesteric and smectic phases arise. Since the optical properties of each of these phases are different, and may be altered depending on alignment within the phase, each gives rise to different electro-optic effects. If these are coupled to the use of dye additives or substituents, then it will be realized that a wide range of electro-optic devices based on dichroism or fluorescence as well as birefringence or scattering power may be fabricated. These will be considered and discussed in terms of their performance and potential applications. Finally, possible uses of polymer-low molar mass liquid crystal solutions will be considered in terms of electro-optic device applications. 

Fig. 9. Schematic dependence of the wavelength of selectively reflected light on temperature for a typical side chain polymer liquid crystal. Tsch denotes the cholesteric to smectic A phase transition and above this temperature the reflected colour changes markedly on heating. Rapid cooling of the material to below Tg stores the reflectance colour obtained during the heating cycle.

In conclusion, we note that although many problems in the theory of liquid-crystalline ordering in polymer systems have already been solved, this area is still in the initial stage of development on the whole. Among the most important directions of further research (cf. [139] for more detail) are the rheology of thermotropic polymer liquid crystals, the theory of liquid-crystalline elastomers, the statistical physics of the surface in liquid-crystalline polymers, the theory of smectic ordering in polymer systems, and the kinetics of phase transitions in liquid-crystal polymCTS. 

Dierking I, Osipov MA, Lagerwall ST (2000) The effect of a polymer network on smectic phase structure as probed by polarization measurements on a ferroelectric liquid crystal. Fur Phys J E... 

Fig. 13.2 Main chain polymer liquid crystal phases (a) nematic, (b) smectic (Collins 2005) [Reproduced with permission from Wiley VCH Verlag GmBH Co]...

Fig. 4.30. Schematic representation of mesogen unit order in the nematic and smectic phases of a main chain/side chain polymer liquid crystal, n is...

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Polymers formed between a and c, d and e all failed to show any liquid-crystalline behaviour. However, for all a examined (m = 2,4,6 and 8), nematic phases were observed with b-4 (all monotropic) - a further monotropic nematic material was the copolymer of a-6 and b-3. Unidentified crystal smectic mesophases were reported for a further three examples. 

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