Showing papers by "Seung Hee Lee published in 2013"

Bienzyme-Functionalized Monodispersed Biocompatible Cuprous Oxide/Chitosan Nanocomposite Platform for Biomedical Application

Abstract: The ultrafine monodispersed cuprous oxide (Ufm-Cu(2)O) nanoparticles have been successfully synthesized by a facile wet chemical method using poly-N-vinylpyrrolidone (PVP) as a capping agent. This colloidal solution of Ufm-Cu(2)O and chitosan (CS) is electrophoretically deposited (EPD) onto the indium tin-oxide (ITO) glass substrate. Thus synthesized nanocomposite has been characterized by X-ray powder diffraction (XRD, ∼6 nm), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopic techniques. This novel biomedical nanocomposite platform has been explored to fabricate a cholesterol biosensor by immobilizing cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) onto Ufm-Cu(2)O-CS/ITO electrode surface. The seed germination tests of these biomaterials (Ufm-Cu(2)O-CS nanocomposite and ChOx-ChEtUfm-CuO(2)-CS nanobiocomposite), conducted using the disc diffusion method, reveal strong activity against the common pathogens and crops, indicating biocompatibility of the nanocomposite. Under optimized conditions, the linearity between the current response and the cholesterol concentration has been obtained in the range of 10-450 mg/dL, with detection limit of 15.9 mg/dL cm(-2) and a high sensitivity of 0.895 μA/(mg/dL cm(-2)). The proposed biocompatible ChEt-ChOx/Ufm-Cu(2)O-CS/ITO bioelectrode shows fast response time (<5 s), good reproducibility, and long-term stability. This biocompatible biosensor has been used to determine the total cholesterol levels in human serum samples. Investigated antimicrobial activities of bienzyme-functionalized Ufm-Cu(2)O-CS nanocomposite are the potential platform for biomedical applications.

Highly Efficient Bienzyme Functionalized Biocompatible Nanostructured Nickel Ferrite–Chitosan Nanocomposite Platform for Biomedical Application

Abstract: A new hybrid nanocomposite based on hydrothermally synthesized nanostructured NiFe2O4 (n-NiFe2O4) and chitosan (CH) has been explored for bienzyme (cholesterol esterase (ChEt) and cholesterol oxida...

A highly efficient rare earth metal oxide nanorods based platform for aflatoxin detection.

Abstract: The nanostructured rare earth metal oxide (samarium oxide, n-Sm2O3) nanorods, prepared using a forced hydrolysis technique, have been electrophoretically deposited (EPD) onto an indium-tin-oxide (ITO) glass substrate. This novel platform has been utilized for co-immobilization of monoclonal antibodies of aflatoxin B1 (Ab-AFB1) and bovine serum albumin (BSA) via electrostatic interactions for food toxin (AFB1) detection. Thus prepared n-Sm2O3 nanorods have been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopic techniques. The results of electrochemical response studies of the BSA/Ab-AFB1/n-Sm2O3/ITO immunoelectrode obtained as a function of aflatoxin concentration reveal a linearity of 10-700 pg mL-1, a detection limit of 57.82 pg mL-1 cm-2, a response time of 5 s and a sensitivity of 48.39 μA pg-1 mL-1 cm-2 with a regression coefficient of 0.961. The association constant (Ka) for antigen-antibody interactions obtained is 47.9 pg mL-1, which indicates high affinity of antibodies towards the antigen (AFB1). The application of n-Sm2O3 modified electrode for immunosensor analysis offers a novel platform and efficient strategy for the application of rare earth metal oxide materials in bioelectronics.

In Situ Homeotropic Alignment of Nematic Liquid Crystals Based on Photoisomerization of Azo‐Dye, Physical Adsorption of Aggregates, and Consequent Topographical Modification

Abstract: In situ homeotropic alignment is achieved by photochromic trans- to cis-isomerization of an azo-dye doped in a nematic host. The augmented dipole moment of the cis-isomer formed under UV-irradiation expedites molecular assembly into crystalline aggregates. Subsequent deposition of the aggregates creates a roughened surface and induces an anchoring transition from the initial planar to a homeotropic alignment of the LCs.

P.101: Investigation on Flexoelectric Effect in the Fringe Field Switching Mode

Abstract: Orientation of liquid crystal (LC) in an on state of the fringe field switching (FFS) mode has splay and bend deformation of LC director, which might cause spontaneous polarization by LC layer itself. Existence of flexoelectric effect is confirmed by observing appearance of flickering while the device is driven by ac voltage. We have tested LC mixtures having positive dielectric anisotropy and studied flexoelectric effects dependent on frequency and temperature.

Dynamic electro-optic response of graphene/graphitic flakes in nematic liquid crystals.

Abstract: Electric field induced dynamic reorientation phenomenon of graphene/graphitic flakes in homogeneously aligned nematic liquid crystal (NLC) medium has been demonstrated by optical microscopy. The flakes reorient from parallel to perpendicular configuration with respect to boundary plates of confining cells for an applied field strength of as low as tens of millivolt per micrometer. After field removal the reoriented flakes recover to their initial state with the help of relaxation of NLC. Considering flake reorientation phenomenon both in positive and negative dielectric anisotropy NLCs, the reorientation process depends on interfacial Maxwell-Wagner polarization and NLC director reorientation. We propose a phenomenological model based on electric field induced potential energy of graphitic flakes and coupling contribution of positive NLC to generate the rotational kinetic energy for flake reorientation. The model successfully explains the dependence of flake reorientation time over flake shape anisotropy, electric-field strength, and flake area. Using present operating scheme it is possible to generate dark field-off state and bright field-on state, having application potential for electro-optic light modulation devices.

Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network.

Abstract: Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles.

A microlens array based on polymer network liquid crystal

Abstract: Using UV light to expose a homogeneous cell containing liquid crystal (LC)/monomer mixture through a patterned photomask, we prepared a polymer network liquid crystal (PNLC) microlens array. In each microlens, the formed polymer network presents a central-symmetrical inhomogeneous morphology and LC exhibits a gradient refractive index distribution. By applying an external voltage to the cell, the gradient of the LC refractive index is changed. As a result, the focal length of the microlens can be tuned. Our PNLC microlens array has the advantages of low operating voltage, easy fabrication, and good stability. This kind of microlens array has potential applications in image processing, optical communications, and switchable 2D/3D displays.

Effects of carbon nanotubes on electro-optic characteristics in vertically aligned liquid crystal display

Abstract: Size- and aggregation-controlled dispersion of thin multiwalled carbon nanotube (t-MWCNT) in negative dielectric anisotropic liquid crystal (LC) material exhibits remarkable improvement in electro-optic response time in vertically aligned LC cells. The physical properties such as birefringence, dielectric anisotropy and clearing temperature of nanotube dispersed LC material appear to be almost invariant to that of pristine LC. Nevertheless, the response time shows noticeable improvement, especially in decaying time associated with transition from maximum to minimum transmission, hence important for faster switching LC devices. The effect is attributed to that vertically aligned t-MWCNTs along the field direction play role of vertical alignment layer between LCs, consequently resulting in increased bend elastic constant of LCs.

Suppressed Crystallization of Rod-Disc Molecule by Surface Anchoring Confinement

Abstract: Upon varying the thickness of liquid crystal (LC) cells and alternating their surface chemical and physical environments, phase transition behaviors of the rod-disc molecule (RD12, where 12 is the number of carbon atoms in each alkyl chain linkage between the rod and the disc mesogens) were dramatically changed. From the cross-polarized optical microscopic observations and analyses, it was realized that the macroscopically oriented nematic (N) phase of RD12 was obtained by the surface anchoring confinement and the crystallization of RD12 was completely suppressed. On the basis of the systematic experimental investigations, it was concluded that the glassy N phase was formed because the interaction between surface alignment layer and RD12 (a surface anchoring force) is bigger than that of RD12 themselves (a driving force of the crystallization). The finely tuned molecular orientations and anisotropic physical properties of the programmed RD12 building compound can allow us to fabricate smart optical and el...

Optical approach to improve the γ curve in a vertical-alignment liquid-crystal cell

Abstract: In this Letter, we propose an optical configuration of a four-domain vertical-alignment (VA) liquid-crystal (LC) cell, which can improve the γ-curve distortion by using a pair of patterned A plates, without any change in cell structure. In order to find the optimal parameter value of the patterned A film, we calculated the polarization difference between the normal direction and the all-viewing direction as functions of the optical axes and the retardation (Δnd) under the voltage applied state. Based on the calculated results, the proposed LC cell showed an improvement in γ-curve distortion of more than 80% in each oblique viewing angle compared to a conventional wide-view VA LC cell, without any loss of optical performance in the dark state.

Vertical alignment of liquid crystals with zinc oxide nanorods.

Abstract: The alignment of liquid crystals (LCs) on zinc oxide (ZnO) nanorods grown vertically on an indium tin oxide (ITO) layer has been investigated as an alternative alignment layer for the vertical alignment of LCs. We found that the degree of vertical alignment strongly depends on the length and density of the vertically aligned ZnO nanorods on the ITO layer and also that a uniform vertical alignment using the proposed structure can be achieved. Finally, vertically aligned LC cells with ZnO nanorods were fabricated and their electro-optical properties were evaluated and compared with those of a conventional vertically aligned LC cell with a polymer alignment layer.

Reduced operating voltage and grey-to-grey response time in a vertically aligned liquid crystal display using a mixture of two polyimide alignment materials

Abstract: We proposed a method to reduce the operating voltage and the grey-to-grey switching time of a vertically aligned liquid crystal display using a mixture of planar and vertical polyimide alignment materials. The surface anchoring energy of the two-polyimide mixture was smaller than that of the pure vertical polyimide and consequently, liquid crystal molecules were easily switched to a planar state with an electric field, resulting in a greater maximum retardation than that of the pure polyimide at the same applied voltage. Rising time was also significantly reduced due to the suppressed optical bouncing effect in the mixed planar polyimide, and the decaying time showed negligible change. With the proposed approach, we can reduce the cell gap to obtain half-wave retardation allowing for faster response time while keeping a low operating voltage. (Some figures may appear in colour only in the online journal)

Preparation of PEDOT/PSSA conductive nanoparticles for dielectrophoretic display

Abstract: Poly(3,4-ethylenedioxythiophene) (PEDOT):poly(styrene sulfonic acid) (PSSA) nanoparticles for dielectrophoretic display were prepared by in situ polymerization of 3,4-ethylenedioxythiophene in the PSSA nanoparticle, which was obtained from the sulfonation of polystyrene nanoparticles prepared by a conventional emulsion technique. The properties of the resulting nanoparticle were characterized by Fourier transform infrared spectrascopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and the dynamic light scattering (DLS) technique. The particle was uniform in spherical shape with an average diameter of ca. 300∼320 nm, and showed high thermal stability up to 340 °C. The electrical conductivity of the PEDOT:PSSA nanoparticle was measured to be as high as 0.11 S/cm. The dielectrophoretic display cell prepared from the colloidal PEDOT:PSSA nanoparticle dispersed in nematic liquid crystal showed significant optical change in response to electric field variation. Open image in new window

P.93: Optically Isotropic Polymer Dispersed Liquid Crystal Composite for High Contrast Ratio and Fast Response Time

Abstract: The optically isotropic polymer dispersed liquid crystal (PDLC) mode has been proposed by confining liquid crystal droplets, with average sizes less than the wavelength of visible light, in polymer network. This state has been achieved via polymerization-induced phase separation (PIPS) method in pre-polymer/LC mixture. The in-plane field driven device shows a complete dark state in voltage ‘off’ under crossed polarizer and excellent white state with induced retardation by Kerr effect in voltage ‘on’ state with an ultrafast response time over a wide temperature range and high contrast ratio.

Electro-optic characteristics of the fringe in-plane switching liquid crystal device for a liquid crystal with negative dielectric anisotropy

Abstract: Fringe-field switching (FFS) liquid crystal (LC) mode is mainly used for high-end LC displays. At present, an LC with positive dielectric anisotropy is utilised, although light efficiency of the device in a white state is not maximised due to generation of tilt angle near the edge of electrodes along the field direction. In order to overcome the demerit, an LC with negative dielectric anisotropy has been challenged. In this article, FFS mode, which shows a high light efficiency and a low operating voltage, is investigated with the utilisation of fringe in-plane electric field. The optimised device shows improved electro-optic characteristics in comparison with not only conventional LC modes, but also previously proposed FFS device using a positive type of LC.

Phase behavior and thermal stabilization study of blue phase liquid crystal-unfunctionalized nanoparticle blends.

Abstract: We have studied the phase behavior of blue phase liquid crystal (BPLC)-unfunctionalized nanoparticle (NP) blends. Two different types of NPs which have different anchoring properties have been studied. Interestingly, Silica NP doped BPLC blends have revealed a small but clear positive shift of the Isotropic-BP phase transition temperature for lower concentration of NPs whereas with higher percentage of NPs we have observed a mixed phase consisted with chiral nematic (N*) and BP. On the other hand, low concentration polyhedral oligomeric silsesquioxanes (POSS) NPs which have stronger anchoring force than Silica NPs have enabled BP to stabilize thermally. Our experimental results agrees with the recent theory predicted that NP-defect interaction strongly depends on the interfacial energy between NP and LC which may be responsible for the observed effects in unfunctionalized NP-BPLC composite system.

Swithcable fresnel lens and fabrication method thereof

Abstract: A switchable Fresnel lens and a fabrication method thereof are disclosed. The switchable Fresnel lens comprises: an upper plate having a first electrode; a lower plate having a second electrode; and a lens cell comprising a liquid crystal layer sealed between the upper plate and the lower plate. The lens cell comprises a Fresnel lens formed by an electric field applied through the first and second electrodes, and having a discontinuous boundary. The lens cell comprises barrier ribs that are vertically formed between the upper plate and the lower plate at the discontinuous boundary of the Fresnel lens.

P.73: WITHDRAWN: P.74: Polymer Stabilized Double Twist Cylinders of Blue Phase Liquid Crystal for Reduced Hysteresis and Operating Voltage

Abstract: In this paper, we have reported a novel method for reducing hysteresis and operating voltage by stabilizing the disclination lines as well as double twist cylinders (DTCs) We have stabilized DTCs by incorporating photo reactive chiral monomer (SRM3) into the monomer mixed host blue phase liquid crystal (BPLC) Hysteresis and operating voltage of the proposed stabilized BPLC is reduced compared to the only disclination line stabilized BPLC

Liquid crystal composition, method of forming an optically isotropic phase of a liquid crystal, and liquid crystal display device including the same

Abstract: A liquid crystal composition including about 70 percent by weight to about 98 percent by weight of a liquid crystal molecule; and about 2 percent by weight to about 30 percent by weight of a hydrogel agent, each based on a total weight of the liquid crystal composition.

Liquid crsytal composition, method for forming optical isotropic phase of liqui cyrstal and liquid crystal display device

Abstract: A liquid crystal composition comprises 70-98 wt% of liquid crystal molecules and 2-30 wt% of a hydrogel agent. The hydrogel agent can contain an alkylamide compound. The liquid crystal composition can form a gel network forming multiple domains which are randomly arranged within a liquid crystal layer. Accordingly, an optical isotropic phase of liquid crystal can be easily formed, and a liquid crystal display which does not have an alignment layer can be implemented.

P.102: Improvement of Gamma Curve Distortion in VA LCD by using Optical Film Patterned Retarder

Abstract: In this paper, we improved the γ-curve distortion at off-axis direction in a 4-domain (4-D) patterned vertical alignment (PVA) liquid crystal (LC) cell by applying a pair of the film patterned retarder (FPR) system with the A-film property at the conventional wide-view (WV) PVA LC cell. In order to achieve the excellent γ-curve in the 4-domain LC cell, we optimized the parameter of the pair of the patterned A-film by using the twodimensional parameter space method, which calculates the polarization difference between the normal direction and the all viewing directions under voltage applied state. As a result, we confirmed that the gamma distortion index (GDI) of the proposed optical structure is reduced to over 80% without any loss of the optical luminance and the contrast ratio in the dark state. Author Keywords Vertical alignment; γ-curve distortion; film patterned retarder; wide viewing angle; transmittance

P.155L: Late-News Poster: Surface Monolayer Stabilized Vertically Aligned Liquid Crystals for Display Applications

Abstract: The surface monolayer stabilized vertically aligned liquid crystal (VA-LC) mode is presented for television applications. Photo-reactive self-assembled monolayer (PR-SAM) is formed on inorganic oxide surfaces. The SAM layer on oxide surfaces initially induce a homeotropic alignment of nematic LCs. Subsequent polymerization of the photo-reactive SAM under applied electric field efficiently stabilizes LC alignment and induces a stable pretilt of LC molecules for four different directions in each pixel of the fishbone-patterned VA-cells. As results, improved electro-optic characteristics, such as faster grey-to-grey response time, lower threshold voltage and enhanced brightness, are obtained after the polymerization-induced stabilization of the photo-reactive SAM.

P.96: Synthesis of Reactive Mesogen and its Stabilizing Characteristics in Polymer Stabilized Vertical Aligned Liquid Crystal Display

Abstract: Four different reactive mesogens (RMs) for polymer stabilization of liquid crystal (LC) director in vertical alignment (VA) display have been synthesized and its stabilizing characteristics depending on size of the synthesized group and polarity of RM have been evaluated by studying electro-optic characteristics of the LC cells. Our results show that the small size of substitute between biphenyls similar to LC molecular with polarity is favored to achieve excellent polymer stabilization without showing any grain size of polymer although photo-initiator is not used at all.