Polymer dispersed LCs

Many other interesting examples of spontaneous reflection symmetry breaking in macroscopic domains, driven by boundary conditions, have been described in LC systems. For example, it is well known that in polymer disperse LCs, where the LC sample is confined in small spherical droplets, chiral director structures are often observed, driven by minimization of surface and bulk elastic free energies.24 We have reported chiral domain structures, and indeed chiral electro-optic behavior, in cylindrical nematic domains surrounded by isotropic liquid (the molecules were achiral).25... 

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... 

MLCs also have their place in optical applications, mainly as so-called polymer-dispersed LCs (PDLCs). A PDLC constitutes a microemulsion of an MLC in a film of a conventional (nonPLC) polymer. In the switched off state the MLC and the polymer have different refractive indices, dispersed MLC droplets (not unlike to the islands in PLCs) scatter light quite effectively, and the film is opaque. Then an external electric field is applied, for instance across a capacitor-like metal coating on both sides of the film. The director in all MLC droplets becomes the same. One can choose the MLC + polymer pair so that the refractive index along the director is the same as that of the host polymer. In that case the film in the electric field becomes transparent. Switching the field off and on, one has a light valve with a fairly large area. 

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... 

Field-induced reorientation of the director with attendant optical changes has recently been used in a novel application with the potential for large-area LCDs polymer dispersed LCs (PDLCs). A PDLC is a microemulsion of MLC dispersed in a conventional transparent polymer film. In the off state there is a mismatch between the refractive index of the MLC and that of the host polymer film. Hence the dispersion of MLC droplets scatters light very effectively, giving an optically opaque film (Fig. 5.14, left-hand side). On application of an external electric field (across a capacitor-like transparent coating of tin oxide on both sides of the polymer film), the director assumes the same orientation in all of the microdroplets. If the... 

D photonic crystals can be made by holographic lithography. Switchable photonic crystals ° can be made by electrically switchable Bragg gratings or holographic polymer dispersed LCs (Fl-PDLC). i... 

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). 

Polymer-dispersed liquid crystals (PDLCs) are made up of nematic liquid crystals dispersed in a solid continuous polymer matrix. These are prepared by mixing a reactive monomer into a non-polymerisable LC medium and then polymerising the reactive monomer to create a polymer matrix, at the same time capturing the LCs as dispersed droplets, greater than 1 pm in diameter, i.e. the wavelength of visible light.3 -33... 

It can be safely predicted that applications of liquid crystals will expand in the future to more and more sophisticated areas of electronics. Potential applications of ferroelectric liquid crystals (e.g. fast shutters, complex multiplexed displays) are particularly exciting. The only LC that can show ferroelectric property is the chiral smectic C. Viable ferroelectric displays have however not yet materialized. Antifer-roelectric phases may also have good potential in display applications. Supertwisted nematic displays of twist artgles of around 240° and materials with low viscosity which respond relatively fast, have found considerable application. Another development is the polymer dispersed liquid crystal display in which small nematic droplets ( 2 gm in diameter) are formed in a polymer matrix. Liquid crystalline elastomers with novel physical properties would have many applications. 

Nano-sized polymer-dispersed liquid crystal (nano-PDLC), voltage-biased PDLC, double-layered homogeneous LC, and double-layered LC gels are aU polarization independent. Compare their pros and cons. 

Polymer-dispersed liquid crystals (PDLCs) are pm-sized dispersions of nematic liquid-crystalline droplets within a polymeric matrix (1-3). They are finding intense interest for applications such as light switches in flat-panel displays and windows (3, 4). They are usually prepared by UV-induced phase separation and cross-linking of a prepolymer containing a compatible blend of liquid crystals (LCs), although solution-casting from a common solvent and cooling from the melt below the upper-critical-... 

The amount of LC added, processing condition, viscosity ratio of the blend components and the rheological characteristics of the matrix decide the size, shape, and distribution of the LC polymer domains in the matrix. Appropriate shear forces are required to obtain good mixing and extensional flow to deform the dispersed LC domains into fibrillar shape. The orientation of LC polymer microfibrils can be increased by drawing, which in turn, improves the mechanical properties of the blend. Discussion of blends processing will follow with several examples. 

Polymer-dispersed liquid crystals (PDLCs) is a relatively new class of promising material for many applications such as, switchable windows, display devices, infrared shutters, angular-discriminating filters, thermoelectrooptic switches, memories, gas-flow sensors, optical sensors, and optical gratings etc. These materials are examples of combined application of polymers and liquid crystals and command the attention of the display industry as well as the researchers. These consist of LC droplets which are dispersed in a polymer matrix. These tiny droplet characteristics are responsible... 

Polymer dispersed liquid crystals (PDLCs) are a relatively new class of composite materials consisting of micrometric liquid crystalline droplets dispersed into a polymer matrix (Bronnikov et al. 2013). Thus, they combine the unique optical properties of liquid crystals (LCs) with the film-forming ability and mechanical properties of a polymer matrix—resulting in appropriate materials for a large variety of fiexible opto-electronic applications (Bouteiller et al. 1996 Bronnikov et al. 2013 Dierking 2000 Drzaic 2006 Kitzerow 1994 Smith 1993). As evidenced by... 

Liquid crystals and colloids have different structures, i.e., there exist colloids dispersed in liquid-crystalline media as either matrices or LC-droplets in an isotropic matrix, prepared in polymer-dispersed liquid crystals. Literature has described the method for the preparation of liquid-crystalline colloidal particles (i.e., photo-crosslinking of dispersion), which leads to large colloidal particles with a broad size distribution [153]. In the latter case, the matrix is hard (crosslinked polymer) and the LC-droplet is mobile. The perfectly inverted system for colloids in a LC-matrix is represented by the liquid-crystalline colloidal particles in a liquid-like isotropic matrix. These studies describe a system prepared by photopolymerization of a nematic liquid-crystalline monomer dispersion in a viscous solvent. The liquid crystalline colloidal particles are manipulated in electrical fields, due to their anisotropic properties. Generally, the anisotropic... 

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