Glassy liquid crystals cholesterics

C. Kim, K.L. Marshall, J.U. Wallace, JJ. Ou, S.H. Chen, Novel cholesteric glassy liquid crystals comprising benzene functionalized with hylnid chiral-nematic mesogens. Chem. 

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. 

The macromolecular nature provides an interesting feature of LC polymeric cholesterics, namely the possibility of obtaining monochromic films. Thus for polymeric liquid crystals the helix pitch is practically not altered with temperature below Tg, when a cholesteric phase is frozen in a glassy matrix (Fig. 23a). This implies that fast cooling of polymeric films from a mesomorphic state (shown with arrows) fixes their optical properties, which makes it possible to use them at ordinary temperatures as selective monochromic reflectors. On the other hand, such polymeric films display the extraordinary polarizing properties of cholesterics, i.e. the different absorption... 

S.K.-H. Wei, S.H. Chen, Spatially resolved lasers using a glassy cholesteric liquid crystal film with lateral pitch gradient. Appl. Phys. Lett. 98, 111112 (2011)... 

Mossbauer studies of glassy nematic [4-6], cholesteric [7, 8] and smectic [9-12] liquid crystals allow the determination of characteristic Debye temperatures, order parameters, intramolecular and lattice contributions to the nuclear vibrational anisotropy, and molecular orientation [13] in the liquid crystal states. For example, Bekeshev et al. have shown from In/ versus temperature data at very low temperatures that MBBA [A -(/7-methoxybenzylidene)-/7-bu-tylaniline] and some liquid-crystalline di-substituted derivatives of ferrocene have weak intermolecular bonds that result in the appearance of additional degrees of free-... 

The cholesteric mesophase is thus very widespread both in natural and in synthetic polymer systems. The capacity of synthetic polymers to retain the properties of cholesteric liquid crystals, primarily the selective reflection of circularly polarized light, in the glassy and highly elastic state, makes them promising materials for creating different optical film elements (selective filters, polaroids, reflectors, heat indicators, etc.). 

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