Polymer stabilized LCs

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

In all the studies discussed, the grating is transmission-type, with the grating vector lying in the sample plane. Using azobenzene-containing polymer-stabilized and polymer-dispersed LCs (PSLCs and PDLCs), Running and coworkers... 

Phosphite polymer stabilizers were analyzed by combining LD/El/FTICR. Used to control molecular weight and color in melt processing, these antioxidants are difficult to analyze by extraction-LC, X-ray fluorescence, UV, or FTIR for a variety of reasons. Xiang et al. examined these additives individually and in mixed polymers that were prepared by hot pressing to form thin films that could be attached to the probe tip. Additives examined included Ultranox 626 (604 Da), XR-2502 (636 Da), and Weston 618 (732 Da). 

In the past few decades the technological possibilities and interests have boosted research in systems in highly restricted geometries in almost every field of physics — recently down to lengthscales close to or even below the molecular level. In the field of liquid crystals, the importance of electro-optical applications which incorporate ordered liquid materials [1-3] has focused the research on LC systems with high surface-to-volume ratio [4]. In order to provide mechanically stable applications, liquid crystals are dispersed in polymers, stabilized by a polymer network, fill the cavities in porous materials, etc. [5,6]. The major technological interest concerns the scattering, reflective and bistable displays, optical switches, and others. 

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... 

Polymer-dispersed LC (PDLC) [30], polymer-stabilized cholesteric texture (PSCT) [31], and LC gels [32] all exhibit optical scattering characteristics and have wide applications in displays and optical devices. The LC gel-based reflective LCD can also be extended to transflective... 

To widen BP temperature range, several approaches have been proposed [15-18] Here, we focus on the blue phases induced by incorporating chiral dopants into a nematic LC host. To make a polymer-stabilized blue phase liquid crystal, a small fraction of monomers (-8%) and photoinitiator (-0.5%) is added to the blue phase system. Figure 14.4 shows some exemplary nematic LC compounds, chiral dopants, and monomers [19]. Then we control the temperature within the narrow blue phase range to conduct UV curing. After UV irradiation, monomers are polymerized to form a polymer network, which stabilizes the blue phase lattice stmctures. 

In a polymer-stabilized self-assembled blue phase system, each material component plays an important role while interacting with the others. In the following, we will discuss the optimization of materials in terms of nematic LC host, chiral dopant, and monomers, respectively. 

The response time of a polymer-stabilized BPLC material is related to the LC parameters as [25] ... 

Figure 14.7 shows the wavelength-dependent Kerr constant of a polymer-stabilized blue phase LC composite studied by Jiao, et al. Dots are the measured data and the solid line is the fitting result with Equation (14.21) using two adjustable parameters 2 216nm and proportionality constant G/E 2.62 X 10 nm This 2 - 216 nm agrees with that obtained from the employed LC host very well. 

Recently, studies of stabilized LC alignment obtained by using polymer networks have been reported. A photocurable monomer is added to the LC, and it is polymerized by UV exposure after the LC has been aligned either by the surface method or by usii electric or magnetic forces. An application for an PTiC was reported based on this approach, and good alignment of the FLC was reported [31]. 

EquaticHi (6.13) clearly reveals that if we can make a significantly large in the composite LC-polymer medium, then we may have Ypsflc YflC which means the polarizatiOTi-tilt ratio shows no improvement due to polymer stabilization. This COTidition is somewhat disadvantageous from the application point of views because the polarizati(Mi-tilt ratio determines the electro-optic response of the medium. Therefore, it is important to identify the possibilities, which can lead a to that critical value for which Ypsflc Yflc- Q e, however, notes that for PSFLCs, a does not change with polymer stabilizatimi (Archer et al. 2008). Therefore, it is expected that PSFLCs may show superior electro-optic properties compared to pure FLCs as a remains fixed. 

Suresh S, Chien LC (2003) Electro-optical properties of polymer-stabilized ferroelectric liquid crystal. Ferroelectrics 287 1-6... 

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