Aligned networks, liquid

Apply the concept of liquid crystal networks crosslink the backbone of NLO side chain liquid crystalline polymers when they are in the liquid crystal phase. In the presence of a mechanical force the resultant sample may be well aligned because of the interaction between the network strands and the side groups. The mechanical effect is equivalent to the electric or magnetic field. The re-orientation response of the liquid crystal is a quadratic function of the applied electric field, but it is linearly proportional to the mechanical stress. Thus, the mechanical stress is more effective in aligning the liquid crystals and is expected to produce less defects and hence to promote the transparency of the sample. 

Polymer Network Stabilized Liquid Crystal Displays. The alignment of liquid crystals plays an important role in the operation of a display. The alignment is conventionally induced by the display cell surfaces, but by distributing the surface of a polymer network through out the bulk of the liquid crystal, new properties are possible, and the performance of conventional devices can be improved. This short section will mention some of the conventional liquid crystal display devices modified by these polymer networks. 

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... 

Liquid Deposition of Highly Aligned Networks of SWNTs... 

Zhao and coworkers [234, 235] reported that an azobenzene polymer network can also optically align ferroelectric liquid crystals. This was done by dissolving two chiral dimethacrylate and one chiral diacrylate monomers containing azobenzene groups in a commercial ferroelectric liquid crystal host. The monomers were illustrated as follows ... 

Polymer networks formed in liquid crystals are anisotropic and affect the orientation of liquid crystals. They tend to align the liquid crystal in the direction of the fibrils. They are used to stabilize desired liquid crystal configurations and to control the electro-optical properties of liquid crystal devices. Polymer networks have been used to improve the performance, such as drive voltage and response times, of conventional liquid crystal devices such as TN and IPS displays. 

Malik MK, Deshmukh RR (2014) Electro-optics of homogeneously aligned nematic liquid crystals stabilized by a polymer network. Int J ChemTech Res 6 1833-1835 Manohar R, Tripathi G, Singh AK, Srivastava AK, Shukla JP, Prajapati AK (2006) Dielectric and optical properties of polymer-liquid crystal composite. J Phys Chem Solids 67 2300-2304 Mei E, Higgins DA (1998) Polymer-dispersed liquid crystal films studied by near-field scanning optical microscopy. Langmuir 14 1945-1950... 

Flory has recently summarized the experimental evidence pertaining to local correlation and their effects on chain dimensions (49). There is experimental support for local alignment from optical properties such as stress-optical coefficients in networks (both unswelled and swelled in solvents of varying asymmetry), and from the depolarization of scattered light in the undiluted state and at infinite dilution. The results for polymers however, turn out to be not greatly different from those for asymmetric small molecule liquids. The effect of... 

The investigation on oriented polymeric networks obtained by the photopolymerization of oriented low molecular weight species, as presented in this paper, has been carried out with a more or less conventional acrylate monomer. Already with this material an anisotropy in properties could be demonstrated. It is to be expected that even more pronounced effects can be obtained with monomers which have a strong tendency to alignment. Based on this idea we are now investigating liquid crystalline monomers in our laboratory. 

Cross-linked liquid crystalline polymers with the optical axis being macroscopically and uniformly aligned are called liquid single crystalline elastomers (LSCE). Without an external field cross-linking of linear liquid crystalline polymers result in macroscopically non-ordered polydomain samples with an isotropic director orientation. The networks behave like crystal powder with respect to their optical properties. Applying a uniaxial strain to the polydomain network causes a reorientation process and the director of liquid crystalline elastomers becomes macroscopically aligned by the mechanical deformation. The samples become optically transparent (Figure 9.7). This process, however, does not lead to a permanent orientation of the director. 

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