Electro-optical Properties Of Films Research Articles

Effects of rigid structures containing (meth)acrylate monomers and crosslinking agents with different chain length on the morphology and electro-optical properties of polymer-dispersed liquid crystal films

ABSTRACTThis contribution investigates the preparation of polymer-dispersed liquid crystal (PDLC) films based on meth(acrylate) monomers containing rigid structures. The current study specifically focuses on comparison of the monomers on the basis of meth(acrylate) side group, flexible/rigid structures and rigidity. We find that methacrylate monomers exhibit more preferable electro-optic properties than that of the acrylate monomers. Furthermore, through the systematic variation of rigidity, composition of the monomers and chain length of crosslinking agents, both the morphologies and electro-optic properties of these films are found to be adjustable. A composite film is demonstrated by employing moderately rigid monomer (tetrahydrofurfuryl methacrylate) with low driving voltage (21.0 V) and high contrast ratio (87.5). Therefore, the studies here provide a new approach to optimize the electro-optical properties of the PDLC films by introducing monomers with rigid structures.

Advancement trends in dye-doped polymer dispersed liquid crystals—a survey review

ABSTRACTAt present there is significant interest in the doping of various types of dyes into polymer dispersed liquid crystals (PDLCs) in display films. Till to date, various types of dyes have been employed to improve the electro-optical properties of PDLC films in various situations by different research groups. Some of the advantageous features of dye-doped PDLC predict that such dye-doping into the PDLC films resolve the scattering effect, improve the films absorbance, enhance the degree of alignment, stability, and the electro-optical properties of the film such as reflectance, contrast ratio and better transmittance. The current article contains a short review on the present and past studies conducted on the dye-doped polymers dispersed liquid crystals films. The fabrication techniques and their various applications in the different display areas are reviewed, along with the new key findings are discussed.

Effects of the structures of epoxy monomers on the electro-optical properties of heat-cured polymer-dispersed liquid crystal films

Polymer-dispersed liquid crystal (PDLC) films were prepared from thermal polymerisation-induced phase separation in heat-curable monomers/nematic liquid crystal (LC) mixtures. For PDLCs with a certain amount of LCs, the microstructure and the refractive index of polymer networks could be influenced by the relative content of epoxy monomers, owing to their different chemical structures. The effect of these factors on the electro-optic properties of films was also investigated.

Influence of the composition of the polymer matrix on the electrooptical properties of films with a dispersed liquid crystal

Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.

Electrooptic properties of films of azopolymers and polycomplexes with donor and acceptor substituents

This paper discusses the absorption spectra of films of new azopolymers and polycomplexes of azobenzene derivatives with cobalt before and during the switching on of an electric field. It has been detected that an external electric field affects the transmission by the films of plane-polarized light at the long-wavelength absorption edge. This effect is caused by spatial reorientation of the dipole moments of azobenzene groups, photoinduced by polarized light in an external electric field. The fact that an electric field affects the transmission of light is explained by the appearance of forces that act on the dipole moments of the azobenzene groups and on the metal ions. The increase of the dipole moment of the azobenzene groups when donor or acceptor substituents are introduced into their composition reduces the influence of metal ions on the electrooptic properties of the polycomplex films.

Electro-optical effect in films of azobenzene polycomplexes with cobalt

Polymeric films containing azobenzene fragments with donor and acceptor groups were produced as well as films of polycomplexes of these fragments with cobalt. Absorption spectra of these films before and during application of an external electric field were investigated. Electro-optical properties of the films are conditioned by spatial reorientation of dipole moments of azobenzene groups induced by polarized light in an external electric field. Increase in dipole moments of azobenzene groups reduces the influence of cobalt ions on the electro-optical properties of the polycomplex films. In the proposed phenomenological model, the electro-optical effect is explained by effect of induced forces upon azobenzene isomers and metallic ions.

Electrical and optical characterization of SiONC dielectric thin film deposited by polymer-source chemical vapor deposition

The electro-optical properties of SiONC dielectric thin films deposited by polymer-source chemical vapor deposition using an organosilane precursor has been investigated as a function of oxygen concentration in the films. SiONC thin films were characterized using capacitance-voltage (C-V), conductance-voltage (G-V), ellipsometry, and ultraviolet visible (UV-Vis) photospectroscopy. These measurements showed that the electro-optical properties of the films are greatly influenced by the atomic concentration of oxygen. The high frequency C-V measurement revealed a nearly ideal metal-oxide-semiconductor (MOS) structure behavior at high atomic concentration of oxygen (35 at. %). A relative dielectric constant as high as 6 is obtained at 10 kHz for samples with about 5 at. % of oxygen, which corresponds to high-k dielectric material. The interface trap density extracted from G-V measurement using Hill-Coleman method is as low as 3.2×1010 (cm−2 eV−1), making these films a viable high-k dielectric alternative to SiO2 and SiON in MOS devices. The refractive index measured by ellipsometry at a wavelength of 632.8 nm shows a linear variation with atomic concentration of oxygen from 1.58 to 1.69. The optical energy band gap extracted from UV-Vis absorption spectra was found to vary between 4.40 and 5.25 eV.

Structural and Electro-Optic Properties of Laser-Ablated Ferroelectric Bi4Ti3O12 Thin Films

ABSTRACTFerroelectric Bi4Ti3O12 thin films have been deposited using second harmonics of a Q-switched Nd:YAG laser. Various single crystal substrates, including SrTiO3(100), SrTiO3(110). MgO(100), and MgO(110), were used. Structural and electro-optic properties of the films were investigated using XRD, x-ray pole figure, and linear birefringence measurements. It is found that substrate kinds and their surface orientations are important growth parameters which determine crystal axis orientation and electro-optic properties of the Bi4Ti3O12 thin films.

Interfacial Interaction between Nematic Liquid Crystal and Polymer in the Composite Film Consisting of Nematic Liquid Crystal and Connected Polymer Microspheres

Thin films composed of nematic liquid crystals in polymer matrices show a reversible optical response from an opaque state to a clear state under the action of an appropriate electric field which aligns the nematic director. Activating voltages of the films are strongly affected by the interfacial interaction between the liquid crystal and polymer. An investigation was performed on films consisting of nematic liquid crystal, micrometer-size polymer microspheres and polymer binders. The microspheres are covered with a thin layer of binders and connected by it. The voids between the microspheres are filled by the liquid crystal. These films were produced using various binders formed from two ingredients. The relationship between the composition of binders and electrooptical properties of films was studied.