Polymer stabilized liquid

Electro-optic materials can be made using liquid crystal polymer combinations. In these applications, termed polymer-stabilized liquid crystals [83,86], the hquid crystal is not removed after polymerization of the monomer and the resulting polymer network stabilizes the liquid crystal orientation. 

The following protocols (6-10) describe the synthesis of some cholesterol-based acrylates and their photopolymerization in an aligned cholesteric phase. The protocols utilize a modification of a system previously described by Shannon. 5 6 ip ie absence of a diacrylate comonomer, the cholesteric phase produced initially on copolymerization is not stable and reverts to a smectic phase on a single cycle of heating and cooling. In the presence of the diacrylate the first-formed phase is stable. This is one example of how crosslinking can stabilise the liquid crystal phase in liquid crystalline elastomers, others include, the so-called, polymer-stabilized liquid crystals and those described in the later protocols. 

Optically Tunable Diffraction Gratings in Polymer-Stabilized Liquid Crystals... 

A modification of the oriented polymer network systems are polymer stabilized liquid crystals (PSLC) 4) being studied in detail because of their application in flat-panel displays. In these materials, photopolymerizable diacrylate monomers are usually dissolved at a concentration less than 10% in non-reactive low-molar-mass liquid crystal solvents, commonly available, along with a small concentration of photoinitiator. Typically, the addition of small amounts of monomers and photoinitiator reduces the transition temperatures of the pure low-molar-mass liquid crystals slightly, suggesting that the order in the system is not dramatically altered by the addition of monomers or initiator. In application, this solution is aligned in a particular desired state and then photopolymerized. Photopolymerization is preferred to thermal free-radical polymerization, because photopolymerizations are very fast and because the temperature of photopolymerization can be controlled more easily to optimize processing of the display. 

Chart I Molecular structure of various solvents and monomers used in the fabrication of polymer-stabilized liquid crystals. 

Figure 5 Schematic representation of morphology evolution in polymer stabilized liquid crystals containing p(BAB). (Reproduced, with permission, from ref. 16 copyright 1996 ACS.)...

Figure 9 Schematic representation of the electro-optic properties of a reverse mode polymer stabilized liquid crystal as a function of the morphology of the polymer network.

Electro-Optic Properties of Polymer Stabilized Liquid Crystals. Polymer networks have been used to stabilize many of the liquid crystal display states in various types of displays quite advantageously. In this section, we present some recent work on correlating the material properties of the liquid crystal/polymer network composite to the electro-optic properties of the flat-panel displays specifically cholesteric texture displays (75) and simple nematic birefringent type displays (7(5). 

The direct correlation between the morphology of a polymer network and the observed electro-optic properties of these reverse-mode PSLC s is noteworthy. Desirable electro-optic response fi om these polymer- stabilized liquid crystals can be obtained by manipulating the structure of the polymer network inside the cells. 

Polymer stabilized liquid crystals are formed when a small amount of monomer is dissolved in the liquid crystal solvent and photopolymerized in the liquid crystal phase. The resultant polymer network exhibits order, bearing an imprint of the LC template. After photopolymerization, these networks in turn can be used to align the liquid crystals. This aligning effect is a pseudo-bulk effect which is sometimes more effective than conventional surface alignment. Several characterization techniques... 

Figure 11.35 Schematic diagram of the polymer-stabilized liquid crystal.

D.-K. Yang. Polymer stabilized liquid crystal displays, in Progress in liquid crystal science and technology. World Scientific, (2012). 

V. V. Presnyakov, K. E. Asatryan, and T. V. Galstian, Polymer-stabilized liquid crystal for tunable microlens applications. Opt. Express 10, 865 (2002). 

H. Kikuchi, M. Yokota, Y. Hisakado, et al.. Polymer-stabilized liquid crystal blue phases, Nat. Mater. 1(1), 64 (2002). 

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