Chih-Yu Chao

Electrically controlled surface plasmon resonance frequency of gold nanorods

We have presented the voltage-controlled tuning of plasmonic response of absorption spectra of gold nanorods in liquid crystals. We observe that gold nanorods can be aligned along the rubbed polyimide substrate before applying external voltage. It is found that the transverse mode of gold nanorods shows a blueshift or a redshift when rotating the analyzer parallel or perpendicular to the rubbing direction, respectively, while all longitudinal modes display a redshift behavior. This work offers an easy way to tune the transverse and longitudinal modes of gold nanorods simultaneously, which makes it feasible to establish the color tunable devices.

Highly conductive PEDOT:PSS films by post-treatment with dimethyl sulfoxide for ITO-free liquid crystal display

In this study, a simple and effective method to enhance the conductivity of poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) thin films from 0.7 to 1185 S cm−1 by post-treatment with dimethyl sulfoxide (DMSO) is demonstrated. After the rubbing technique was applied, the DMSO-treated PEDOT:PSS film could be used as both the transparent electrode and the alignment layer to fabricate ITO-free liquid crystal (LC) cells. The electro-optical properties of LC cells fabricated by the rubbed PEDOT:PSS were comparable to those constructed by ITO and polyimide. This work indicates that the highly conductive PEDOT:PSS film is a promising material for ITO-free LC devices.

Effect of insulating-nanoparticles addition on ion current and voltage-holding ratio in nematic liquid crystal cells

The transient currents induced by an applied direct voltage (dc) electric field have been measured liquid-crystal cells in nematic phase. The experimental results show that the addition of insulating nanoparticles, such as diamond powders, leads to a reduction of the ion concentration in cells so as to drastically reduce the transient currents and threshold voltage. Simultaneously, a high voltage-holding ratio (VHR) in doped cells is observed. Such a high VHR, in comparison with nematic liquid crystals doped by carbon nanotubes, is a superior feature for future liquid crystal display applications.

Effect of Doped Insulating Nanoparticles on the Electro-Optical Characteristics of Nematic Liquid Crystals

Presenting information is essential in many aspects of our daily life. Among all display systems, liquid crystal display (LCD) occupies more than half of the display market as a whole on account of many advantages, including the flat panel, small weight, high definition, small driving voltages, and low power consumption. Currently, almost all LCDs are manufactured with nematic liquid crystal (LC) mixtures. And one of the most common modes for nematic LC displays is twisted nematic (TN) mode. Although the nematic LCs are the dominant materials in display market and for switchable optical devices, the degrading tendency of the performance is undoubtedly a significant barrier for practical applications. The performance of a LC device is mainly affected by the alignment layers and the LC mixtures used. One of the most crucial causes of performance degradation for nearly all the LCDs is the flowing ions within the LC devices. These ions may come from the LCs, the alignment layers, the surrounding glue, be generated by ultraviolet polymerization, or be produced during the filling

Lighting, font style, and polarity on visual performance and visual fatigue with electronic paper displays

Visual performance and visual fatigue of electronic paper displays (electrophoretic display and cholesteric liquid crystal display) under ambient illuminances and light sources were studied and compared with paper. Forty-eight participants participated in a character-search task in the experiment. The results showed that search speed depends on the illuminance but not light source. Search speed increased as illumination increased from 300 lx (45.6 sec), 700 lx (44.18 sec) to 1500 lx (43.24 sec). The effect of medium display and polarity on accuracy was also significant. Accuracy was greater for electrophoretic display and positive polarity. However, the effect of illuminance and light source on visual fatigue was not statistically significant. Based on the results of this study, it seems that E-paper displays may need greater illumination (700 lx or higher).

Supramolecular Liquid-Crystal Gels Formed by Polyfluorene-Based π‑Conjugated Polymer for Switchable Anisotropic Scattering Device

To overcome the problem of high driving voltage and low contrast ratio in the switchable scattering device of conventional liquid-crystal (LC) physical gel, a new type of supramolecular LC physical gel has been developed and fabricated through the fibrous self-assembly of the polyfluorene-based π-conjugated polymer, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), in nematic LC mixture E7. It was found that the rubbed interface between the LC molecules and polyimide layer can induce the LC physical gels to demonstrate fantastic light scattering characteristic. The gels with oriented self-assembled supramolecular structures exhibiting significant anisotropic light scattering in the main-chain direction of the F8BT molecules under an extremely low driving voltage (ca. 2.7 V) are reported for the first time. In addition, the contrast ratio can be reached exceeding 1000. In contrast to conventional LC physical gels, the large reduction of driving voltages of the supramolecular gel provides great possibility for application in various electro-optical devices such as tunable polarizers, transflective displays, and polarized light modulators.

An integrated microfluidic system for diagnosis of the resistance of Helicobacter pylori to quinolone-based antibiotics

Helicobacter pylori (H. pylori) is a species of bacteria that can colonize the human stomach mucosa. It is closely associated with gastric diseases such as ulcer and inflammation. Recently, some H. pylori strains were found to express resistance to a family of antibiotics known as quinolones due to single-point mutations. Although traditional polymerase chain reaction (PCR) and molecular diagnostic-based approaches can be used to determine the presence and abundance of antibiotic-resistant H. pylori strains, such processes are relatively expensive, labor-intensive, and require bulky and costly equipment. This study therefore reports an advanced diagnostic assay performed on an integrated microfluidic system for rapid detection of antibiotic resistance in H. pylori. The assay features three components: (1) nucleic acid extraction by specific probe-conjugated magnetic beads, (2) amplification of the target deoxyribonucleic acid (DNA) fragments by using single-nucleotide-polymorphism polymerase chain reaction (SNP-PCR), and (3) optical detection of the PCR products. The device integrates several microfluidic components including micro-pumps, normally-closed micro-valves, and reaction chambers such that the entire diagnostic assay can be automatically executed on a single microfluidic system within one hour with detection limits of 10(0), 10(2), and 10(2) bacterial cells for H. pylori detection and two different SNP sites strains. Three PCR-based assays for determining presence of H. pylori infection and two DNA single-point mutation assays aimed at determining whether the infected strains were resistant to quinolone can be performed simultaneously on a single chip, suggesting that this microfluidic system could be a promising tool for rapid diagnosis of the presence of antibiotic-resistant H. pylori strains.

Alignment control of liquid crystal molecules using crack induced self-assembled grooves

Molecule alignment has many significant applications in biotechnology, molecular electronics, optoelectronic devices and liquid crystal (LC) display manufacturing. In this paper, we employ a fast and high-throughput method, fabricating micro- and nano-grooves for the alignment of liquid crystal (LC) molecules. Splitting the polymer film sandwiched by two substrates triggers the propagating wave front to induce self-assembled grooves on the polymer surfaces. This crack-induced grooving (CIG) method not only avoids the high-temperature process, dust and ion contaminations caused by traditional rubbing, but also provides a large anchoring energy comparable to that using polyimide rubbing. This CIG method offers an appealing alternative to existing technologies for LC molecules alignment.

Influence of particle size on the ion effect of TiO2 nanoparticle doped nematic liquid crystal cell

In this study, the transient currents of nematic liquid crystal cells doped with different sizes of titanium dioxide (TiO2) nanoparticles were measured. The experimental results illustrate that doping TiO2 nanoparticles into nematic liquid crystals leads to a reduction in the moving-ion density and the amount of reduced impurity ions is related to the size of doped TiO2 nanoparticles. Under the same doping concentration, TiO2 nanoparticles with a smaller average particle size are more effective in trapping the impurity ions. The measurements of voltage–transmittance curves and time evolution characteristics of the doped liquid crystal cells further confirm this phenomenon. This study suggests that TiO2 nanoparticles with a smaller size are better candidates as nanodopants for liquid crystal display applications.

Photopolymerized self-assembly microlens arrays based on phase separation

In the past decades, there has been much effort in developing and improving new techniques for the production of microlens arrays. Here a low-temperature self-assembly method using phase separation is demonstrated for the first time for the fabrication of polymer microlens arrays. In this paper, we present a simple method for producing microlens arrays based on liquid crystal/photopolymer blends via phase separation. The morphology of the microlens arrays has been measured by SEM, AFM and scanning white light interferometry. Our results show that the microlens arrays obtained from our experiments have a comparable light-gathering capability and can be applied in optical systems.