Polymer-stabilized liquid crystals PSLCs

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. 

Binary mixtures of a flexible polymer and a rigid rod-like molecule (nematogen or liquid crystal) play an important role in electro-optical devices, such as light shutters and displays. Since the miscibility or phase separation controls the performance of the materials, the phase behavior and phase separation kinetics have been of fundamental and practical interests. Liquid crystalline domains dispersed in a polymer matrix are called polymer dispersed-liquid crystals (PDLCs), or polymer-stabilized liquid crystals (PSLCs), where the polymer forces the liquid crystals to phase separate into droplets surrounding by the polymer matrix [2]. Practically, there are many ways to create PD LCs by mixing polymers and liquid crystals the emulsion method [37] and phase separation method [38], including polymerization-, thermally-, and solvent-induced phase separations. The reader is referred to text books [1, 2] for details of PDLC and a review [39] for the rheological and mechanical properties. 

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. 

After polymerization, polymer networks tend to stabilize the state in which they are formed. In a PSLC, the liquid crystal near the polymer network is ahgned along the polymer network. The strength of the interaction between the liquid crystal and the polymer network is proportional to the surface area of the polymer network. The surface area of the polymer network can be increased by using higher polymer concentrations or producing smaUer lateral size polymer networks. 

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