Chi-Chang Liao

A polarizer-free flexible and reflective electrooptical switch using dye-doped liquid crystal gels.

A polarizer-free flexible and reflective electro-optical switch using dye-doped liquid crystal (LC) gels is demonstrated. The electro-optical performances of both scattering and absorption based dye-doped LC gels depend on curing temperatures due to domain sizes of polymer networks. Such flexible electro-optical switch is bendable and trim-able because of the vertical polymer networks and gel-like materials. The dye-doped LC gel shows good reflectance ~55%, good contrast ratio~450:1 and fast response~6.4 ms at curing temperature 10 degrees C. The bending curvature is 21 mm. The dye-doped LC gels open a new window for trim-able electronic papers, decorative displays, electrically switchable curtains, and electrically switchable sun control film for the automobiles, homes or commercial buildings.

Characteristics of nanoparticle-doped homeotropic liquid crystal devices

We have found that nanoparticles of polyhedral oligomeric silsesquioxane (POSS) can induce vertical alignment in nematic liquid crystal (LC) cells as long as the doped weight percentage of POSS in the LC cells is higher than ~1%. Such nanoparticle-induced vertical alignment (NIVA) is a very suitable technique for application in the low-temperature fabrication of plastic LC displays. The dynamic process of LC orientation from randomly parallel alignment to vertical alignment was recorded, and it is posited that the POSS NIVA is due to the adsorption of POSS on the inner surfaces of the LC cells. The influence of the POSS concentration on the electro-optical properties and dielectric constant of LC cells was also investigated and the results indicate that LC cells doped with ~1 wt% POSS provide the best electro-optical performance.

Nanoparticles-doped guest-host liquid crystal displays

The technique, nanoparticles-induced vertical alignment (NIVA), was applied to fabricate a guest-host liquid crystal display (GH-LCD) without conventional alignment layers. The GH-LCD produced by NIVA exhibited a high reflectance of approximately 59% in the voltage-off state and a low threshold voltage of approximately 2.1 V(rms). NIVA is very suitable to be applied for fabricating a plastic LCD requiring a low temperature process, and a flexible timepiece by using NIVA was demonstrated.

Optical simulation of cholesteric liquid crystal displays using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is a powerful numerical algorithm used to directly solve Maxwells equations. We introduce the idea of the FDTD method and the techniques required for optical simulation of cholesteric liquid crystal (Ch-LC) devices. Bragg reflection characteristics of Ch-LC cells are investigated using the FDTD method. Three approaches to broadening the bandwidth of Bragg reflection are demonstrated: (1) using a higher birefringence LC, (2) using a cell with a gradient pitch length, and (3) using a cell with a new multidimensional structure of a Ch-LC.

Flexible and reflective polarizer-free liquid crystal displays using dye-doped liquid crystal gels

A flexible and reflective polarizer-free display using dye-doped liquid crystal (LC) gels is demonstrated. The electro-optical performances of both scattering and absorption based dye-doped LC gels depend on curing temperatures. The dye-doped LC gel shows good reflectance ~55%, good contrast ratio~450:1 and fast response~6.5ms at curing temperature 10 °C when UV curing intensity is 2.6 mW/cm2. The EO performance depends on the curing temperature. The hysteresis is independent of sampling time duration. The bending curvature is 21 mm. The response of dye-doped LC gels is faster under bending due to the bending-induced sheared force of polymer networks. The dye-doped LC gels open a new window for trimable electronic papers, decorative displays and switchable curtains.

P-34: Influences of Anti-reflection and Anti-glare Surface Treatments on Legibility and Visual Fatigue of Reflective-type Displays

Influences of anti-reflection and anti-glare surface treatments, radius of curvature and ambient illuminance on legibility and visual fatigue of reflective-type displays were studied. The results showed that legibility and visual fatigue mainly depended on the surface treatment, and better surface treatment can improve legibility and reduce visual fatigue especially in the intense ambient illumination. Surface treatments of 0.8% anti-reflection and 44% anti-glare show the same visual performance.

31.2: Effect of Character Size and Lighting on Legibility of Electronic Papers

Effects of character size under ambient illuminance and light source on legibility of electronic papers were studied. Legibility was evaluated by a letter-search task. The results showed that search speed increased with illuminance level and character size. However, the effect of illuminance and light source on search accuracy was not statistically significant.

P-168: Reflective Type Polarizer-Free Flexible Displays Using Dye-Doped Nematic Liquid Crystal Gels

A polarizer-free flexible display using a dye-doped nematic liquid crystal (LC) gel is demonstrated in reflective mode and transmissive mode. By mimicking the display principle of a paper, combing both scattering and absorption, such a bendable and trim-able LCD exhibits∼55% reflectance, ∼450:1 contrast ratio in reflective mode, ∼20:1 contrast ratio in transmisive mode, and 15 ms response time. A single pixel flexible reflective display using such dye-doped LC gels is also demonstrated under bending and cutting. The minimal bending radius of curvature is ∼21mm.

Polarizer-Free Gradient Dye-Doped Liquid Crystal Gels

A multi-switch display using gradient dye-doped LC gels which is still polarizer-free, fast response (∼10ms in general), and high contrast (∼200:1 in general) has demonstrated. By controlling the spatial distribution of the density of polymer networks through fabrication process, gradient dye-doped LC gels can be a multi-switch. The gradient dye-doped LC gel is bright without applied voltage and is dark at a high voltage. It appears the colored pattern when LCs are partially reoriented due to the gradient density of polymer networks. The optical analysis of dye-doped LC gels is also discussed. The potential applications are flexible display and decorative displays.

Polarizer-free liquid crystal displays

A reflective polarizer-free liquid crystal display (LCD) using dye-doped LC gels is demonstrated. The main mechanism is to combine dye absorption and polydomain scattering. The potential applications are electronic papers and flexible displays.