Jiunn-Yih Lee

Preparation of dye-doped polymer-dispersed liquid crystals using acrylic monomers, and enhancement of contrast by using THF solvent as a cleaning agent

Polymer-dispersed liquid crystal (PDLC), with characteristics of high contrast and low driving voltage, has found many product applications and is an important material for new generations. In this experiment, we used 2-phenoxy ethyl acrylate (2-PEA) and tripropylene glycol diacrylate, two acrylic monomers, to prepare PDLC, and we compared various preparation conditions in order to investigate the impact of structural properties on the optical behavior of PDLC. While maintaining the low driving voltage and high contrast of a PDLC, a dichroic dye was added to turn the device into a dye-doped PDLC. Using a polarized light microscope, it was observed that direct injection of the dye resulted in an overflow of the dichroic dye outside the thin film, reducing the contrast of the PDLC. Therefore, we utilized tetrahydrofuran solvent to wash away the liquid crystal (LC) from the PDLC, followed by re-addition of the dye-containing LC. This successfully solved the dye overflow problem and was found to enhance the PDLC contrast effectively.

Blend Uniformity of a Filament and Staple Composite Yarn and Its Effect on Dyeing

This study describes the effect of spread width and spreading behavior on the blend uniformity of a cotton/polyester filament blend yarn and the latters effect on dyeing. The results show the wider the spread width, the more uniform the spreading among individual filaments. Higher blend uniformity also ultimately results in more uniform dyeing. The spread width of polyester multifilament yarn is controlled while passing through the spreading electrode and condenser during the spinning process, which greatly improves blend uniformity and ultimately dyeing evenness.

Effect of oil composition on physical properties and spread width of polyester multifilament for spinning a composite yarn

Abstract This study examines the effect of oil composition (including the anti‐static agent ‐ alkyl ether sulfate) on the physical properties and spread width of polyester multifilament for spinning a composite yarn. The results show that the solid content and viscosity of a special oil are slightly lower than normal oil, which reduces the stickiness of the spreading multifilament. Also, the coefficient of kinetic friction μk and electrical conductivity of oiled polyester multifilaments are higher than normal oil in order to conduct and store charges, and to divide easily and spread widely to maintain good spreading performance. The content of the anti‐static agent is the most important component of a special oil. For example, the amount of alkyl ether sulfate (RO(CH2CH2O)nSO3Na) should be 14% to reduce electrical resistance, and increase spreading performance. Furthermore, the number n of oxyethylene groups(CH2CH2O) on alkyl ether sulfate is 2 or 3 in order to maintain a lower electrical resistance and w...

Optimizing the SmCP phase bent-core mesogen characteristics by introducing dimeric liquid crystals

This article demonstrates a method to simultaneously enhance the electro-optical properties and decrease the mesophase temperature of MD-H bent-core liquid crystals by introducing organosiloxane dimeric liquid crystals, C11Si2C11 and C11Si3C11. The differential scanning calorimetry, spontaneous polarization, and switching time were systematically studied. It has been shown that the MD-H bent-core liquid crystals doped with 20% dimeric liquid crystals have lower mesogen temperatures, faster switching times, and lower rotational viscosities.

Synthesis and mesomorphic properties of novel liquid crystal series with two chiral centres and their electro‐optic characteristics

Abstract Three series of novel chiral liquid crystals containing biphenyl moiety with two chiral centres (diastereomer) were synthesized and characterized. The structures and thermal phase behaviour of target compounds were characterized using 1H nuclear magnetic resonance, mass spectroscopy, elemental analysis, differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. All the compounds exhibit enantiotropic mesomorphic behavior. In this case, the chiral liquid crystalline molecules bearing the shorter length of alkyl chain (m = 3 and 4) show a mesomorphic dimorphism SmA*‐N* and the analogous compounds bearing the longer length of alkyl chain (m = 5 and 6) exhibit only one SmA* mesophase. Furthermore, the potential of SmA* mesophase for electro‐optics applications exploiting the electroclinic effect was explored. The electro‐optical properties of the SmA* phase, such as voltage‐transmittance effect, electroclinic effect, and electro‐optical response were also measured. As a consequence, the correlation between their electro‐optical properties and chemical structures of these compounds were investigated.

The effects of chiral dopant and monomer concentration on the electro-optical characteristics of reverse-mode PSDFCT cells

Using chiral dopant and monomer in specific concentrations, a high-contrast bistable light shutter using reverse-mode polymer-stabilized dual-frequency cholesteric textures was successfully developed. On applying a low/high-frequency electric field, the light shutter was switched between transparent and non-transparent states, which were maintained even after the electric field was removed. Therefore, the proposed light shutter is extremely energy efficient and can be incorporated into the construction of smart windows for green buildings.

Optical discrepancy in the mosaic texture of NOA65 photopolymer transfer printed using phase-separated PS/PMMA surface structures treated with cyclohexane

In this paper, we studied the physical and optical properties of the mosaic-textured surface of NOA65 photopolymer transfer printed indirectly using thin layers of phase-separated PS/PMMA blend. The immiscible, phase-separated PS/PMMA blend was spin-coated onto a glass surface and treated with cyclohexane to form the mosaic texture, then the texture was used to transfer print onto UV-curable NOA65 photopolymer with PDMS used as an indirect transfer bridge. The PS/PMMA membrane had three phase-separated sub-thin layer structures: the top PS-rich layer, the interlayer PS/PMMA blend, and the underlying PMMA-rich layer. Using a selective solvent (cyclohexane), the PS phase of the membrane surface was dissolved to form the mosaic structure. By transfer printing the mosaic structures of different textures indirectly onto NOA65, three varieties of surface structure were formed: Non-continuous mosaic textures, smooth surfaces with many interior indentations, and more obvious mosaic structures. The NOA65 photopolymer not only has favorable elasticity, rendering it rollable and malleable, but our experimental observations also revealed that as there are samples with 60% PS and samples with 40% PMMA, transfer printing onto the more evenly distributed mosaic texture on the NOA65 surface enabled it to have self-cleaning effects, such as hydrophobicity and not easily attracting dust (the so-called lotus effect) as well as possessing high optical transmittance, and low reflectance with minimal HAZE value (HAZE value often is expressed as clarity). These features can be applied to many common optical components such as screens or glass display cabinets.

The study of the helical pitch of cholesteric liquid crystals by introducing achiral rod-like molecules

To design and synthesize achiral rod-like ester compounds, 4-n-octyloxybiphenyl-4′-octyloxybenzoate. The compound is similar to 4-octyloxyphenyl 4-octyloxybenzoate, which could provide expectantly with effects like chiral materials. n-4′-methoxybenzylidene-n-butylaniline (MBBA) is also an achiral rod-like molecule, which is not chiral in terms of conformation. Two compounds were added to a mixture with several types of cholesteric liquid crystals that are liquid crystals at room temperature, and it was found that the helical pitch of cholesteric crystals that were mixed with 4-n-octyloxybiphenyl-4′-octyloxybenzoate was inclined to become longer. The other compound, MBBA, added in cholesteric liquid crystals made helical pitch shorter. The results are the same as when chiral molecules are added to cholesteric liquid crystals.

Studies of the bistable mechanism in electro-thermal switching polymer-stabilized cholesteric texture light shutters

Our research studied the bistable mechanism in electro-thermal switching reverse polymer-stabilized cholesteric texture (ET-RPSCT) light shutters. The bistable mechanism in ET-RPSCT is a result of a polymer distortion effect induced by applying a high-voltage pulse. It was found that long-pitch cholesteric liquid crystals will maintain a focal conic texture by a distorted polymer network which exhibits a translucent state. An annealing treatment method was used to recover cholesteric liquid crystals back to the planar texture through alignment layers. We compared the ET-RPSCT cells in different polymer network structures, which were built from different UV curable diacrylate monomers and concentrations, resulting in different anchoring forces and polymer distortion effects. We found that when the polymer network structure is tight and fiber-like, the long-pitch cholesteric liquid crystals are more stable in the focal conic texture because of polymer distortion, and are resistant to switching states. On the other hand, the long-pitch cholesteric liquid crystals recover to the planar texture easily by thermal switching due to a loose and grain-like polymer network structure. Furthermore, the effects of polymer structure on the electro-optical performance of ET-RPSCT were also investigated.

The mixtures of chiral and non-chiral tilted smectic C liquid crystals which contain wide ferroelectric phase

A new liquid crystal of a siloxane dimer with an achiral swallow-tail, C11Si3C11, was synthesized and mixed with a chiral material as a chiral dopant, 4′-[11-(1,1,2,2,3,3,3-heptamethyltrisiloxanyl) undecyloxy) biphenyl-4-carboxylate, C11Si3 , to prepare binary mixtures for this study. The mesophases under consideration were investigated by means of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and electro-optical experiments. The influence of the mixture proportion of C11Si3 on the occurrence of the chiral smectic C (SmC*) phase was investigated. Finally, the electro-optical properties of the SmC* phase such as tilt angle, dielectric permittivity, and switching behavior were also measured. As a consequence, the correlation between the electro-optical properties and mixture proportion was determined.