Development of Personal UV Biodosimeter Based on Vitamin D Photosynthesis

Abstract

A new approach to monitoring of vitamin D synthetic capacity of UV solar/artificial radiation is described. Nematic liquid crystal (LC) was converted into cholesteric phase by chiral dopant of 7-dehydrocholesterol (provitamin D₃), and the effects of UV irradiation were studied using spectral and polarized observations. Significant changes in optical characteristics of the LC films depending on UV exposure were observed as a result of UV initiated photoisomerization that changed helical twisting power of dopant molecules.     

The effects of surface morphological mechanics on liquid crystal alignment characteristics using photo-activators

Abstract

Photo-activators, which produce carbon dioxide, are highly reactive radical generators upon UV light illumination. In this study, the generated radicals selectively reacted with the polyimide (PI) main chains and created a liquid crystal alignment layer with a high level of azimuthal anchoring energy. The thickness of the photo-irradiated PI alignment layer was reduced dramatically by photo-induced radical crosslinking, which induced surface wrinkling and roughness. Moreover, the carbon dioxide and methane gases that were generated during photo-irradiation produced many micro-pores, which also attributed to holding the LC molecules tightly on the PI surfaces. The level of azimuthal anchoring energy that was obtained by photo-alignment was better than what was obtained by the rubbing method with the same PI, specifically, the maximum value of the photo-alignment with the photo-activator was 6.92 x 10^?5 J/m² than 1.11 x 10^?5 J/m² of the rubbing. We proposed a mechanism based on a high anchoring energy, a rough surface, a hydrophilic surface, and rapid photo-reactions.     

Phenomena induced by UV irradiation in PbMoO4 single crystal

Abstract

Electrical properties and optical absorption of PbMoO₄ single crystal were studied after UV irradiation. Anomalies of permittivity ε and conductivity σ were detected and attributed to the dipole centers induced by UV light. It was proposed that dipole centers were created by photoelectrons trapped by Mo within oxygen tetrahedra distorted by an oxygen vacancy V_O. At high temperatures conductivity was nearly insensitive to UV irradiation. Additional optical absorption was observed in PbMoO₄ single crystal after UV irradiation. It was argued that transfer of photoelectrons from lead to molybdenum groups was responsible for the photochromic effect found.     

Optical limiting action of 2-amino 5-nitro pyridinium chloride crystal for laser safety devices

ABSTRACT

The liquid crystal (LC) displays with narrow bezel design require excellent physical properties such as high adhesion, low moisture permeability, and low LC contamination. Among the adhesive components, the heat curing agent is an important component in the adhesive and plays a key role in the adhesion between the epoxy resins. In this study, new UV/heat dual-curable adhesives involving a multi-functional heat-curing agent of branched polyethylenimine have been prepared and evaluated by adhesive strength, moisture permeability, and LC contamination measurements. It is shown that the proposed adhesives offer excellent adhesive properties for narrow-bezel applications.     

The Role of Host Molecules in the Crystalline Inclusion Compounds: Hexamethylenebis(trimethylammonium) dications as guest species

ABSTRACT

This report demonstrates hybrid homeotropic alignment of liquid crystals (LCs) using a self-assembled molecular (SAM) layer. 4-(4-Hep-tylphenyl)benzoic acid forms a SAM layer through hydrogen bonding with indium-tin oxide (ITO) substrate, and the LCs were aligned vertically without a polyimide (PI) layer on one side of substrate. The proposed hybrid structure featured a more stable homeotropic alignment than the LC device (LCD) with only half of a PI layer, and showed electro-optical characteristics similar to conventional LCDs with full PI layers. The SAM layer showed stable alignment and fast response in the LC cell by a simple doping method.     

Fabrication of Pre-tilted Vertical Alignment Layers for High-Speed Liquid Crystal Display Using Bi-functional Photoreactive Monomers

Abstract

To enable recent 3D and moving picture applications, liquid crystal displays (LCD) must exhibit fast response and wide viewing angle characteristics. Pre-tilted vertical alignment layers for high-speed LCD were fabricated using bi-functional photoreactive monomers. The monomers can be confined to the polyimide layer and photo-polymerized by UV exposure under voltage. Response characteristics of photo-controlled alignment films according to the structure were investigated. Vertical alignment properties were evaluated using a polarizing optical microscope, and electro-optical characteristics were compared through the voltage-transmittance curve and response time measurement. Faster response speed could be obtained by using photoreactive monomers having a long alkyl chain.     

The effect of concentration and molecular weight of polycarbonate on the elastic constants of a nematic liquid crystal solvent

A polarized upconverting luminescence in a novel upconverison nanorods (UCNRs)/liquid crystal network polymer (LCN) composite film is proposed. The UCNRs were fabricated by hydrothermal method, which were further modified to be introduced into LCN precursors with good dispersion. The orientation of UCNRs in LCN precursors was found to be strongly influenced by the configuration of LC molecules which could be modulated by external electric field. The UCNRs/LCN composite films in planar and homeotropic configuration were fabricated by UV photopolymerization. It is demonstrated that upconverting fluorescence emission from the UCNRs/LCN film with planar orientation is polarization-dependent, while the emission from the UCNRs/LCN film with homeotropic alignment is not polarized. These observations are ascribed to the directional arrangement of the UCNRs enabled by the LC molecules alignment and the crystal symmetry of the UCNR matrix. This work paves a different avenue to the construction of the upconversion nanoparticles/polymer composite system with prospective application value in anti-counterfeiting optical films.     

Glass Dispersed Liquid Crystals

Abstract

Liquid crystals can be trapped into inorganic (silica) substrates by sol-gel processes. The sol-gel process consists of hydrolysis and polycondensation reactions of metal organic monomers, i.e. organoalkoxy silanes, which allows the formation of a silica gel-glass. These processes have been used since 1984 for trapping organic molecules into inorganic oxides; usually, single molecules are trapped into isolated gel-glass (nm size) pores. However, it is possible, by chemical means, to induce larger (0.1–10 pm) cavities in the network of the gel-glass allowing the formation of embedded micron size droplets of low molecular weight nematic LC molecules. Surface variations in these cavities (e.g., providing a molecular oriented surface using Si-CH,CH, groups on the pore cage) may allow a lamellar structure and alignment of the nematogenic LC compounds at the surface. It was suggested that order arises as a consequence of the chemical affinity between the apolar character of the pore surface and the lipophilic groups of the LC. Therefore, the main concern has been to ascertain whether the sample manufacturing keeps the LC structure, thus giving gel-glass dispersed liquid crystals (GDLCs) with electrooptical response.     

Fabrication of half-polyimide-less liquid crystal device with fast response using reactive self-aligning amphiphile

ABSTRACT

We propose a new vertical alignment method for fast switching liquid crystal displays (LCDs) without the polyimide alignment layer on one side of a substrate. The key to this new method is the use of the amphoteric 2-carboxyethyl acrylate, which combines reactive acrylate and carboxylic acid groups to allow hydrogen bonding with substrate. The reactive group can achieve pre-tilt for a fast-switching of LC molecule, and the hydrogen bonding allow for vertical alignment of LC. The amphoteric material enables the manufacturing of cost-effective LCDs by reducing the number of steps in the process and fast switching by establishing pre-tilt alignment.     

Fabrication of a fast-switching liquid crystal device using reactive self-assembled polyimide alignment layer

ABSTRACT

We proposed a new vertical alignment method for simultaneously improving the alignment force and electro-optical properties. The key point of the new method is the self-assembly of the reactive monomer via hydrogen bonding with the polyimide alignment layer and the formation of pre-tilt using the reactive monomer on an alignment layer. Through the self-assembly of the reactive monomer and the generation of the pre-tilt, it is possible to obtain a higher alignment force and a fast response time. As a result, through a simple additional step, we can fabricate a fast-switching liquid crystal device using a reactive self-assembled alignment layer.     

Liquid Crystal Alignment Behaviors of Polystyrene Derivatives Containing Coumarin Moieties

We synthesized a series of polystyrene derivatives containing coumarin side groups, poly(7-(4-vinylbenzyloxy)coumarin) (P7COU#) and poly(7-(4-vinylbenzyloxy)4-phenylcoumarin) (P7COU4P#), where # is the molar content of 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin, respectively, using polymer analogous reaction, in order to study the effect of the 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these two series was investigated by photoalignment or rubbing alignment. The LC cells made from photoirradiated P7COU# and P7COU4P# films showed homogeneous planar LC alignment. We found that LC aligning ability of the LC cells made from rubbed P7COU# and P7COU4P# films were affected by the structure and molar content of coumarin side groups. For example, anchoring energy of the LC cell fabricated with rubbed P7COU82 (7 × 10^?5 J/m²) and P7COU4P81 (7 × 10^?7 J/m²) film was increased drastically and slightly compared to polystyrene (10^?7?10^?8 J/m²), respectively. Particularly, anchoring energy of the LC cell made from rubbed P7COU# having more than 51 mol % of the 7-hydroxycoumarin as a side groups is comparable to that of the conventional polyimide in the LCD industry.     

Multirings Aromatic Aldehyde Liquid Crystal with Azo Linkage and Their Photosensitivity in Mesophase

Ten new rod-like aromatic aldehyde liquid crystalline molecules with azo linkage were synthesized, in which bi(trans-cyclohexyl), cyclohexyl phenyl, and biphenyl carboxylic acid mesogenic cores with terminal ethyl, n-propyl, n-butyl, and n-pentyl substituents were esterified with azo benzoic aldehyde. These molecules were designed in an attempt to construct a series of new azo liquid crystalline molecules to investigate the influence of ultraviolet (UV) light on their mesophase. All compounds have been characterized on the basis of their spectral data, differential scanning calorimeter (DSC), and hot stage polarizing optical microscope (HS-POM). All these compounds exhibited liquid crystalline phase that belonged to nematic and photosensitive properties. Their temperature ranges of mesophase are from 101 °C to 150 °C. Under irradiated 365 nm UV light, they showed photosensitivity in the solvent of methanol. Observed under HS-POM, the UV light also did change the textures of these compounds. The result showed that terminal ethyl is enough for these molecules to exhibit wider temperature range of mesophase, and these new molecules have photosensitivities observed under illumination of UV light not only in solution but also in mesophase due to the change of their structures from trans isomer to cis one.     

Polystyrene Blend Alignment Layers for Pretilt Angle Control of Liquid Crystal

We prepared blend alignment layer based on polystyrene containing 7-hydroxycoumarin (P7COU) and polystyrene containing 2-naphthoxy (P2NAP) side groups for liquid crystal (LC) alignment. The LC cells made from the rubbed P7COU/P2NAP blended films exhibited a shift of the LC alignment direction by approximately 20° compared with those made from a polystyrene film. Stable and homogeneous planar LC cells having pretilt angles adjustable from 0° to 5° were obtained from these polymer films having molar contents of P7COU and P2NAP in the ranges of 100–80 and 0–20 mole%, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films.     

LC alignment behaviors on polystyrene blend alignment films

We prepared blend alignment film based on 4-ethylphenoxymethyl-substituted polystyrene (P4EP) and polystyrene (PS) for liquid crystal (LC) alignment. Stable and uniform LC cells having pretilt angles adjustable from 90^o to 0^o were obtained from these polystyrene blend films having weight contents of P4EP and PS of 1 and 100 weight %, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene blends having good solubility in many organic solvents and their films having low process temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.     

Alignment Properties of Some Polymeric Layers

Orientational properties of rubbed thin polymer layers with vinylic backbone and different side groups are presented. Some of these polymers lead to the alignment of LC molecules parallel to the rubbing direction whereas other polymers impose a perpendicular orientation. The stability of the obtained alignment as function of the temperature was tested.     

Tunable Liquid Crystal Lens Based on Pretilt Angle Gradient Alignment

The new method of LC lenses fabrication based on innovative alignment material for pretilt angle gradient generation is developed. The alignment layer provides LC lens pretilt angle gradient via two-step treatment: uniform rubbing and gradient nonpolarized UV exposure. LC lens has uniform cell-gap, 2–10 V tunable voltage range. The fabrication method is scalable for lens arrays for two-dimensional/three-dimensional autostereoscopic and light-field displays.     

Liquid Crystal Alignment Behavior on Rubbed Films of Cellulose Acetate

The liquid crystal (LC) alignment behaviors of LC cells fabricated with cellulose acetate films were investigated. These polymer films exhibited good optical transparency in the visible light region (400–700 nm). For example, transmittance value (92%) of the cellulose acetate film onto glass substrate at 550 nm is better that (89%) of the polyimide (PI) film, the most commonly used LC alignment layers. These LC cells fabricated with the rubbed cellulose acetate films showed the homogeneous planar LC alignment with parallel direction with respect to the rubbing direction. The electro-optical characteristics of the LC cells made from the cellulose acetate films such as response time were as good as those fabricated from rubbed PI films.     

The Function of Self-Assembled Polyfluorene-Based π-Conjugated Supramolecular Structures Formed in Twisted Nematic Liquid Crystals

We demonstrate that the supramolecular structure can be formed through the fibrous self-assembly of the polyfluorene-based polymer F8BT in liquid crystal (LC) 5CB. With the utility of alignment layer, the F8BT molecules can be aligned and formed oriented polymer network. We found that the presence of oriented polymer network makes twisted nematic LC exhibit excellent electro-optical properties (EO) of driving voltage reduction and EO bump peak elimination. The polyfluorene-based supramolecular structure provides the function of stabilizing LC molecules. We consider this functional self-assembled network has potential to apply in various devices for the ability of improving performance in operating property.     

Small molecular electrolytes as the interlayer for enhanced performance of organic solar cellsExperimental

Abstract

New non-conjugated small molecules (C4-OH and C6-OH) were synthesized and applied to the inverted organic solar cells (OSCs) as the cathode interlayer (CIL). The power conversion efficiencies (PCEs) of 9.35 and 9.21% were obtained in the device based on ZnO/C4-OH and ZnO/C6-OH, which are better than those of pristine ZnO (8.74%). The work function of ZnO/C4-OH and ZnO/C6-OH are also decreased from ?4.5?to ?4.27?eV and ?4.37?eV, respectively. Consequently, OSCs with two small molecules exhibited enhanced photovoltaic properties due to the formation of interface dipole.     

Optical properties of azo-based poly(azomethine)s with aromatic fluorinated fragments,ether linkages and aliphatic units in the backbone

Abstract

The aim of this work is to study the optical properties of the core-fluorinated azo-containing polyazomethines with 1,4-tetrafluorobenzene or 4,4′-octafluorobiphenylene dioxyphenylene units and aliphatic fragments in the chain. Due to the reorganization process at the nanometer-scale under UV/Vis irradiation, azo-containing polymers (APs) have attracted much attention as materials for biology, optoelectronics, nano-manipulation field, etc. Moreover, the introduction of azomethine group into these polymers enhances not only their optical properties but also expands their practical application. APs polymers have the useful combination of chemical and physical properties such as liquid crystalline states, high nonlinearity and an ability to form metal complexes. It was shown that the optical properties of such polymers could be improved by the inclusion of fluorine. Fluorinated polymers demonstrate high thermal stability and have low dielectric constant and dielectric losses. It should be noted that the presence of flexible moieties in a polymer backbone allows regulating the different properties (solubility, thermostability, optical and liquid crystalline properties) of the final materials.