Polymer-stabilized Blue Phase Liquid Crystal Research Articles

Polymer-stabilized blue phase liquid crystal devices with ultra-low hysteresis and driving stability

Hysteresis is a critical factor that plays a significant role in determining the electro-optical performance of display devices, especially in polymer-stabilized blue phase liquid crystal devices (PSBPLCDs). The presence of hysteresis limits the accuracy of device operation and affects its long-term stability. To address this challenge, we have employed a few short-chain monofunctional methacrylate monomers at an appropriate concentration to form microscale network holes in PSBPLCDs. These PSBPLCDs with microscale network holes show low hysteresis (<0.5 %) for networks with non-smooth surfaces and even ultra-low hysteresis (∼0.02 %) for networks with smooth surfaces. The PSBPLCDs exhibit a wide temperature range exceeding 85 °C and have similar response times to that of conventional PSBPLCDs. Moreover, these PSBPLCDs have a low hysteresis and small residual birefringence even after undergoing 2,000,000 driving cycles. These research results are significant in determining the appropriate selection of monofunctional monomers for the design and development of PSBPLCDs.

A Review of Developments in Polymer Stabilized Liquid Crystals.

Polymer-stabilized liquid crystals (PSLCs) are multi-functional materials consisting of polymer networks in a continuous phase of liquid crystals (LCs), of which polymer networks provide anchoring energy to align the LCs. A number of improvements are detailed, including polymer-stabilized nematic liquid crystals (PSNLCs), polymer-stabilized cholesteric liquid crystals (PSCLCs), polymer-stabilized blue phase liquid crystals (PSBPLCs), polymer-stabilized smectic liquid crystals (PSSLCs), polymer-stabilized ferroelectric liquid crystals (PSFLCs), and polymer-stabilized antiferroelectric liquid crystals (PSAFLCs) in this review. Polymer stabilization has achieved multiple functionalities for LCs; in smart windows, a sufficiently strong electric field allows the LCs to reorient and enables switching from a scattering (transparent) state to a transparent (scattering) state. For broadband reflectors, the reflection bandwidth of LCs is manually tuned by electric fields, light, magnetic fields, or temperature. PSBPLCs open a new way for next-generation displays, spatial light modulators, sensors, lasers, lenses, and photonics applications. Polymer networks in PSFLCs or PSAFLCs enhance their grayscale memories utilized in flexible displays and energy-saving smart cards. At the end, the remaining challenges and research opportunities of PSLCs are discussed.

Sub-microsecond electro-optic response in polymer-stabilized dual-frequency blue phase liquid crystals

Sub-microsecond electro-optic response in polymer-stabilized dual-frequency blue phase liquid crystals

Formation of monodomain polymer-stabilized blue phase liquid crystals using surface acoustic waves.

This work uses surface acoustic waves (SAWs) that are generated by a piezoelectric substrate containing an interdigital transducer (IDT) to which a low voltage of 2 mV was applied at a frequency of 1 kHz to fabricate a polymer-stabilized blue phase liquid crystal (PS-BPLC) layer. The PS-BPLC layer has a more uniform optical microscope (OM) image at a voltage of 2 mV than at zero voltage, and its reflective spectrum exhibits a smaller full width at half maximum (FWHM) at the former than at the latter. The uniform OM image and small FWHM reveal that the lattices in the PS-BPLC layer have monodomain structure. The monodomain PS-BPLC layer is formed because the SAWs cause longitudinal and transverse vibrations of the PS-BPLC lattices in the vertical plane along their traveling direction. The proposed method for fabricating the monodomain PS-BPLC layer using the SAWs has potential for the development of reflective optical devices that consume low power during their fabrication.

Over 200 °C Broad-Temperature Lasers Reconstructed from a Blue-Phase Polymer Scaffold.

Blue-phase liquid crystal (BPLC) lasers have received extensive attention and have potential applications in sensors, displays, and anti-counterfeiting, owing to their unique 3D photonic bandgap. However, the working temperature range of such BPLC lasers is insufficient, and investigations are required to elucidate the underlying mechanism. Herein, a broad-temperature reconstructed laser is successfully achieved in dye-doped polymer-stabilized blue-phase liquid crystals (DD-PSBPLCs) with an unprecedented working temperature range of 25-230 °C based on a robust polymer scaffold, which combines the thermal stability and the tunability from the system. The broad-temperature lasing stems from the high thermal stability of the robust polymerized system used, which affords enough reflected and matched fluorescence signals. The temperature-tunable lasing behavior of the DD-PSBPLCs is associated with the phase transition of the unpolymerized content (≈60 wt%) in the system, which endows with a reconstructed characteristic of BP lasers including a U-shaped lasing threshold, a reversible lasing wavelength, and an obvious lasing enhancement at about 70 °C. This work not only provides a new idea for the design of broad-temperature BPLC lasers, but also sets out important insight in innovative microstructure changes for novel multifunctional organic optic devices.

Light-focusing phenomena of field-tuned micro-lens made of polymer-stabilized blue phase liquid crystals

The analytical distribution of the electric field in a micro-lens made of polymer-stabilized blue phase liquid crystals (PS-BPLCs) between two electrodes has been derived, and ray bending and focusing for the o (ordinary) and e (extraordinary) rays caused by the field-induced extended Kerr effect on the PS-BPLC have also been calculated. Those calculations show that the focal lengths of most o rays are longer than those of e rays. The o and e rays result in a focal length of 11.6 cm at a Kerr constant of 2.3768 nm/V2 close to the experimental data, and the calculated focal spot diameter is about 80.0 μm. If the Kerr constant is decreased to 2.14 nm/V2, we can obtain a focal length of 13.1 cm, the same as the experimental data. This reduction in the Kerr constant is reasonable because it is still within the experimental error. In summary, our calculations reveal an efficient and accurate way to discuss the focusing phenomena in the PS-BPLC micro-lens.

Low-voltage and fast-response polymer-stabilized blue-phase liquid crystals achieved using a new organosilicone monomer.

In this paper, two types of polymer-stabilized blue-phase liquid crystals (PS-BPLCs) with different monomers were designed and prepared. The morphology, temperature range and electro-optical properties of the blue phases were studied and discussed. The temperature range of both types of PS-BPLC is greater than 110 °C, and both samples can be stabilized well at room temperature. The organosilicone monomer 3-methacryloxypropyltrimethoxysilane (KH570), which contains double bonds, was introduced to a blue-phase system for the first time. Regarding the electro-optical performance, the on-state voltage of the PS-BPLCs with the KH570 monomer is reduced to 30 V compared with traditional C12A monomer systems in which the on-state voltage is 75 V at 458 nm. Meanwhile, a fast response and suppressed hysteresis are obtained. These results are helpful to the application of displays and photonic devices.

Effect of Amorphous Crosslinker on Phase Behavior and Electro-Optic Response of Polymer-Stabilized Blue Phase Liquid Crystals.

Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5–3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400–500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red.

Optimal content ratio and total content of polymer monomers in polymer stabilized blue phase liquid crystal displays

ABSTRACT In polymer-stabilised blue-phase liquid crystal (PSBPLC) display, we have obtained that the optimal content ratio of the polymer monomers RM257 and C12A is 1.225 according to the ideal bonding condition, and the total content of polymer monomers with the lowest hysteresis effect and residual birefringence is 7.5 wt.% through experiment. The polarising optical microscope and scanning electron microscope micrographs show that the polymer network structure of this ratio and this content is uniform, the spatial distribution is obvious, and the optical domain structure of the blue phase is uniform. The hysteresis effect and residual birefringence of the PSBPLC display are 0.84% and 0.55%, respectively. The research results have an important guiding significance for designing PSBPLC devices.

Polymer-stabilized blue phase liquid crystal sensor for sensitive and selective detection of organic vapors

ABSTRACT Polymer-stabilised blue-phase liquid crystal (PS-BPLC) is a soft artificial three-dimensional photonic crystal (PC) functional material for optics and optoelectronics because of its superior optical properties. In this work, we demonstrated that PS-BPLC film could sense and selectively detect the xylene, heptane, cyclohexane, dichloromethane and ethyl alcohol vapours rapidly and accurately. When the PS-BPLC film was alternately exposed to volatile vapours and air, the Bragg reflection wavelength of the PS-BPLC could reversibly and significantly shift because of the adsorption and desorption of the volatile vapours. Different organic vapours could be well discriminated by the linearity and the critical concentration at which the Bragg reflection disappeared. This organic vapour sensor also had a good sensitivity, high repeatability, humidity independence and long-term stability, which promote a widespread use in environmental monitoring, point-of-care biomedical analysis and optical security coatings.

Effect of a Trifluorophenyl-Based Monomer on the Electro-optic Performances of Polymer-Stabilized Blue Phase Liquid Crystals

We synthesized one novel mono-functional acrylate monomer. The effect of the new monomer on blue phase liquid crystal stabilization and electro-optical properties was investigated with different reactive polymer concentration and combination. The temperature range of blue phase samples was widened over 50 ° C including room temperature through the use of polymer stabilization. Electro-optical properties including lower driving voltage (69.8 V), lower hysteresis (3.9%), lower response time (0.468 ms), and higher Kerr constant (9.4 nm/V2) were obtained by optimizing the concentration of different composites. They are strongly influenced by the interface energy between the liquid crystal molecules and polymer combination system. It is found that hysteresis is sensitive to the polymer concentration.

P‐146: Electrically Tunable Bandpass Filter with Narrow Bandwidth of 27 nm

We propose an electrically tunable narrow bandwidth bandpass filter in which the band gap of polymer stabilized blue phase liquid crystal (PS‐BPLC) with distinct crystallographic orientations can be tuned on electric field sweeps from red to blue with a narrow bandwidth (27 nm). Owing to the narrow bandwidth which can cut specific wavelength, it could be used as a filter to enhance color gamut in LCDs. In addition, the proposed bandpass filter exhibits much wider viewing angle property than Cholesteric LC bandpass filter.

Chiral polymer network stabilised blue phase liquid crystals

ABSTRACT The effect of chiral polymer network in polymer-stabilised blue phase liquid crystals (PS-BPLCs) is investigated. Compared with the conventional polymer network, the chiral polymer network can induce and stabilise the blue phase with less proportion of chiral dopant and monomer. Benefiting from twisting power and good compatibility of the chiral monomer, the driving capability of chiral PS-BPLC can be much improved by 65% compared with that of conventional PS-BPLCs. The hysteresis and residual birefringence issues also can be improved by introducing a chiral monomer with high stiffness and small molecule weight.

Thermal stability and electro-optical characteristics of polymer stabilised blue phase liquid crystalline materials: a role of polymer concentration

ABSTRACT Polymer stabilised blue phase liquid crystals (PSBPLCs) perpetually boost the advancement for next-generation display technologies and optoelectronics. Herein, a series of polymer concentration dependent PSBPLC samples have been prepared using nematic liquid crystal (BL036), chiral dopant (CB15) and mono, di-functional monomers (EHA, RM257). A systematic and detailed study of polymer concentration effect on textures and electro-optic properties have been investigated. Platelets like textures with considerable BPs range were perceived for three polymer concentrations (6.5 wt.%, 8.5 wt.%, 10.5 wt.%) whereas no such BPs were recognised for 5.0 wt.% and 12.5 wt.% precursors. Interestingly, a noteworthy wide BP temperature range of ~ 38°C was observed in 8.5 wt.% precursor based PSBPLC sample. The electro-optical parameters like induced birefringence, residual birefringence, hysteresis, operating voltage and Kerr constant were also measured to support the applicability of the present material.

Electrically switchable band-edge laser based on polymer-stabilized blue phase liquid crystal

ABSTRACT An electrically switchable band-edge laser has been demonstrated in a dye-doped polymer-stabilised blue phase liquid crystal. The light intensity of the laser can be tuned in three-dimensional space with a switching time of submillisecond, which promotes this band-edge laser widespread use in displays, point-of-care biomedical analysis, and optical security coatings.

Polymer‐Stabilized Monodomain Blue Phase Diffraction Grating

AbstractThe structural beauty of liquid crystalline blue phases is attested not only by their colorful optical micrographic textures but also by optical isotropy. More importantly, the homogeneity of the structures influences greatly to the electro‐optic properties. In this work, how the lattice orientation in polymer‐stabilized blue phase liquid crystal (PS‐BPLC) diffraction grating affects phase‐modulated diffraction efficiency is elaborated. A well‐arranged monodomain structure of blue phase is achieved and its diffraction capability is compared with multidomain PS‐BPLC. The diffraction efficiency in the zeroth order of monodomain PS‐BPLC is improved by 9% compared to that of multidomain structure. In addition, both driving and threshold voltages in monodomain PS‐BPLC are decreased by 29% and 30%, respectively, compared to those in multidomain PS‐BPLC owing to the regular arrangement of cubic lattices that give rise to increase in the coherence length and unified response in molecular reorientation under electric fields. Furthermore, the monodomain PS‐BPLC shows an efficient polarization conversion of linear polarization into circular polarization. It is believed that the device exhibits great potential to be used as a polarization converter or beam steering devices.

Spatially and electrically tunable random lasing based on a polymer-stabilised blue phase liquid crystal-wedged cell

ABSTRACTWe demonstrate a spatially and electrically tunable random lasing based on polymer-stabilized blue phase liquid crystal (PS-BPLC)-wedged cell. The spatially tunable random lasers can be obtained from the laser dye-doped PS-BPLC-wedged cell through changing the pump positions, where the emission wavelength of the random laser can be tuned due to the thickness gradient of the wedged cell, which affects the scattering mean free path. Additionally, applying different electric fields can also tune the laser emission wavelength. The changing of refractive index due to the Kerr effect leads to a change in the scattering mean free path, resulting in shift of lasing wavelength. This PS-BPLC-wedged cell device has a great potential in applications of speckle-free imaging, document coding, biomedicine and other photonic devices.

Hysteresis-free and fast response polymer-stabilised blue phase liquid crystals

ABSTRACTThe electro-optical properties of γ-Fe2O3 nanoparticles doped polymer-stabilized blue phase liquid crystals are investigated. The experimental results show that the hysteresis were effectively suppressed by doping γ-Fe2O3. When doped with γ-Fe2O3 of 1.0 wt. %, hysteresis-free and fast response were achieved by the coupling effect of polymer and nanoparticle. Our research provides excellent guidance for the development of electro-optical devices with high grey scale accuracy and fast response.

Effect of a Dual Functional Polymer on the Electro-Optical Properties of Blue Phase Liquid Crystals.

The effects of the fluorinated monomer with an ethynyl group on the electro-optical properties of polymer-stabilized blue phase liquid crystals (PSBPLCs) were investigated in different polymer systems. In rigid polymer systems, the Kerr constant can be increased by about 27.6%, while keeping a microsecond response time. In soft polymer systems, hysteresis decreased by about 45.5% and residual birefringence can be reduced from 1.85% to 0.6%. The above phenomena exhibited dual functions of affecting the anchoring energy and the viscosity of the system simultaneously. The results provide a potential value for the ethynyl-containing monomers in PSBPLC systems.

P‐148: Chiral Polymer Network of Polymer‐stabilized Blue Phase Liquid Crystals

The effect of chiral polymer network in polymer‐stabilized blue phase liquid crystals (PS‐BPLCs) was investigated. Compare with the conventional polymer network, the chiral PS‐BPLCs may induce and stabilize the blue phase with less proportion of chiral dopant resulting in a higher Kerr constant. The hysteresis and residual birefringence may be improved by introducing a chiral monomer with more rigid structure. And the response time is little effected by the chiral polymer network.