Yi-Fen Lan

Concentration effect of carbon nanotube based saturable absorber on stabilizing and shortening mode-locked pulse

We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was from 1 to 4.5% as the thickness increased 18 to 265 microm. The full-width half-maximum (FWHM) of the stable mode-locked EDFL (MLEDFL) pulse decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps as the thickness of SWCNTs SA increased 8 to 100 microm. With an erbium-doped fiber length of 80 cm, the shortest pulse width of 1.85 ps were achieved at 1.56 microm with a repetition rate of 11.1 MHz and 0.2 mW of the output power under an output coupling ratio of 5%. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.

Observation of Carbon Nanotube and Clay Micellelike Microstructures with Dual Dispersion Property

Micellar microstructures of carbon nanotubes (CNTs) with clay platelets were formed by physically pulverizing both materials in powder form. The resultant CNT-clay mixtures were enabled to decrease the level of aggregation of the CNTs from their original state in water as well as in organic mediums including toluene, dimethylformamide, and ethanol. The presence of clay significantly enhanced the CNT dispersion in the following trend: anionic synthetic fluorinated mica (300 x 300 x 1 nm(3)) > anionic sodium montmorillonite (80 x 80 x 1 nm(3)) > cationic layered double hydroxide (200 x 200 x 1 nm(3)). Both geometric dimensions and ionic charge could be the predominant factors for decreasing the CNT entanglement. The CNT-Mica demonstrated an amphiphilic property for dispersing in water and toluene, but in an irreversible manner. It is explained that the original CNT and clays noncovalent bonding forces are randomized during the contact with solvent. The formation of micellelike microstructures, resembling oil-in-water and water-in-oil surfactants, was proposed. Ultraviolet-visible absorbance and transmission electronic microscopy have verified the existence of two different microstructures, which also exhibited differences in thermal stability (600 vs 650 degrees C onset temperature) by thermal gravimetric analysis as well as electrical conductivity (10(-4) vs 10(-6) S/cm).

Optical rotatory power of polymer-stabilized blue phase liquid crystals

Macroscopically, a polymer-stabilized blue phase liquid crystal (BPLC) is assumed to be an optically isotropic medium. Our experiment challenges this assumption. Our results indicate that the optical rotatory power (ORP) of some nano-scale double-twist cylinders in a BPLC composite causes the polarization axis of the transmitted light to rotate a small angle, which in turn leaks through the crossed polarizers. Rotating the analyzer in azimuthal direction to correct this ORP can greatly improve the contrast ratio. A modified De Vries equation based on a thin twisted-nematic layer is proposed to explain the observed phenomena.

Optimized blue-phase liquid crystal for field-sequential-color displays

We report an optimized blue phase liquid crystal (BPLC) mixture JC-BP08 for field-sequential-color (FSC) display applications. JC-BP08 exhibits several attractive features: 1) its fast average gray-to-gray response time enables FSC display, which in turn triples the resolution density and optical efficiency. 2) Its voltage holding ratio is >99.4% at 25°C and >93.2% at 60°C. 3) Its average dielectric constant e’≈87 is still manageable by the bootstrapping driving to enable 240 Hz operation. 4) Using a triangular protrusion electrode structure, the transmittance can reach 74% at 15V, which enables single-TFT driving. 5) With two-domain structure, it offers indistinguishable gamma shift and wide viewing angle. We proposed a voltage charging model and found a linear relationship between the required charging time and e’, which is validated by our experimental results.

Hydrophobic Modification of Layered Clays and Compatibility for Epoxy Nanocomposites

Recent studies on the intercalation and exfoliation of layered clays with polymeric intercalating agents involving poly(oxypropylene)-amines and the particular uses for epoxy nanocomposites are reviewed. For intercalation, counter-ionic exchange reactions of clays including cationic layered silicates and anionic Al-Mg layered double hydroxide (LDH) with polymeric organic ions afforded organoclays led to spatial interlayer expansion from 12 to 92 Å (X-ray diffraction) as well as hydrophobic property. The inorganic clays of layered structure could be modified by the poly(oxypropylene)amine-salts as the intercalating agents with molecular weights ranging from 230 to 5,000 g/mol. Furthermore, natural montmorillonite (MMT) clay could be exfoliated into thin layer silicate platelets (ca. 1 nm thickness) in one step by using polymeric types of exfoliating agents. Different lateral dimensions of MMT, synthetic fluorinated Mica and LDH clays had been cured into epoxy nanocomposites. The hydrophobic amine-salt modification resulting in high spacing of layered or exfoliation of individual clay platelets is the most important factor for gaining significant improvements of properties. In particular, these modified clays were reported to gain significant improvements such as reduced coefficient of thermal expansion (CTE), enhanced thermal stability, and hardness. The utilization of these layered clays for initiating the epoxy self-polymerization was also reported to have a unique compatibility between clay and organic resin matrix. However, the matrix domain lacks of covalently bonded crosslink and leads to the isolation of powder material. It is generally concluded that the hydrophobic expansion of the clay inter-gallery spacing is the crucial step for enhancing the compatibility and the ultimate preparation of the advanced epoxy materials.

Low-voltage blue-phase liquid crystal display with diamond-shape electrodes

ABSTRACT We propose a new electrode configuration, called diamond-shape in-plane switching, to lower the operation voltage of polymer-stabilised blue-phase liquid crystal (BPLC) displays (BPLCDs). The electrode structure is modified from conventional protruded IPS, where the strip protrusion is changed to diamond shape. By optimising the electrode gap and diamond length, we are able to obtain peak transmittance over 75% at 15 V. It enables single thin-film transistor (TFT) driving, and more importantly, this is based on an industrially proven BPLC material. That means good long-term stability, adequate TFT charging time for high-resolution displays and sub-millisecond response time and acceptable voltage-holding ratio for field sequential displays can be achieved simultaneously. Our device design helps accelerate the emergence of the long-awaited BPLCDs. GRAPHICAL ABSTRACT

Turning film for widening the viewing angle of a blue phase liquid crystal display

We report a new turning film structure for widening the viewing angle of a vertical-field-switching blue-phase liquid crystal display, which employs a directional backlight. The turning film consists of periodic prismatic structures: each period has three prisms with different base angles so that the output light can be spread to a larger angle. Simulation results show that a full width at half-maximum of ±80° in the horizontal direction and ±45° in the vertical direction can be achieved.

Compensation Film Designs for High Contrast Wide-View Blue Phase Liquid Crystal Displays

The polarization rotation effect of blue phase liquid crystal (BPLC) composite causes light leakage in the dark state, which in turn degrades the contrast ratio. We propose three approaches to compensate the light leakage and thereby improve the contrast ratio and widen the viewing angle of a BPLC display. The merit and drawback of each design are also discussed.

Hierarchical synthesis of silver nanoparticles and wires by copolymer templates and visible light

Self-assembled silver wires in micro-meter scale were obtained from aqueous silver nitrate solution in the presence of a comb-like copolymer as the sole organic component. The requisite copolymer was easily prepared by the grafting poly(oxyethylene)-monoamine (POE-amine) onto poly(styrene-co-maleic anhydride) (SMA). Upon storage at ambient temperature with exposure to daylight, the aqueous AgNO(3)/SMA-POE solution gradually underwent a color changed from transparent pale-yellow to dark-violet over a period of hours, and after several months a solid precipitate was deposited. The formation process was monitored by ultraviolet-visible spectrometer, particle size analysis, scanning electron microscope, and transmission electron microscope. Silver wires were hierarchically formed by progressive transformation from the initial appearance of silver nanoparticles (ca. 10nm in diameter), followed by the intermediate rectangles (0.6-1.0μm in width and 0.4μm in length) in solution and ultimately the precipitates in micro-scale of silver wires at 1.6-6.4μm in diameter and 100-370μm in length. The progressive formation of the precipitated silver wires was accelerated by the exposure of visible light as a photo-reducing energy source. The micron-scale wires have a silver content over 97.4wt.% and a sheet resistance of 5.5×10(1)Ω/square.

Identification of polymer stabilized blue-phase liquid crystal display by chromaticity diagram

We reported an identification method of blue phase liquid crystal (BPLC) display status by using Commission International de l’Eclairage (CIE) chromaticity diagram. The BPLC was injected into in-plane-switch (IPS) cell, polymer stabilized (PS) by ultraviolet cured process and analyzed by luminance colorimeter. The results of CIE chromaticity diagram showed a remarkable turning point when polymer stabilized blue phase liquid crystal II (PSBPLC-II) formed in the IPS cell. A mechanism of CIE chromaticity diagram identify PSBPLC display status was proposed, and we believe this finding will be useful to application and production of PSBPLC display.