Polymer-stabilized Blue Phase Research Articles

Study of polymer-stabilised blue phase liquid crystal on a single substrate

ABSTRACTOne outstanding feature of the polymer-stabilised blue phase (PSBP) is that it is unnecessary to form an alignment film, which requires a high-temperature baking process. Therefore, PSBPs may enable flexible liquid crystal displays (LCDs) on plastic substrates. In this study, polymer stabilisation of a blue phase (BP) on a single substrate was performed without using a conventional sandwich-type cell, and the electro-optical properties are demonstrated to be similar to those of a sandwich-type PSBP LCD cell. It was experimentally shown that the oxygen which inhibits radical polymerisation is required to be excluded in order to complete the polymer stabilisation in blue phase.

Comparison of electro-optical switching between polymer-stabilised cubic and amorphous blue phases

We prepared polymer-stabilised cubic and amorphous blue phase liquid crystals consisting of the same materials at different UV-curing temperatures using photopolymerisation. Then we investigated the effects of polymer stabilisation on their physical properties. The UV-curing temperature does not affect phase stabilisation of the polymer-stabilised amorphous BPIII (PS-BPIII). Temperatures of the PS-BPIII were found to be extended to more than 50 K. However, a critical temperature exists in the polymer stabilisation process for the PS-cubic BP. Although no substantial difference in response speed was found between the polymer-stabilised cubic and amorphous structures, larger hysteresis and higher residual birefringence were observed in the PS-cubic BP than in the PS-BPIII. Amorphous BPIII with an amorphous network of disclination lines has no critical temperature for the polymer stabilisation and realises a high-performance display.

Polarization-independent refractive-index change of a cholesteric liquid crystal

Refractive index of a cholesteric liquid crystal (chiral pitch: 5 μm) was evaluated in the infrared region to realize a polarization-insensitive device. The liquid crystal exhibited an isotropic refractive index, since its helical microstructure was too small to recognize with a long-wavelength infrared beam (2–8 μm). No polarization dependence appeared in interference spectra of a Fabry-Perot filter that consisted of the liquid crystal and silicon plates. The refractive index of the LC, which was evaluated from the interference peak wavelengths, changed from 1.58 to 1.49 as applied voltage increased from 0 to 18 V. This index change was close to theoretical prediction and greater than that of a polymer-stabilized blue-phase LC.

P‐167L: Late‐News Poster: Enhanced Stability, Hysteresis, and Dark State of Polymer‐Stabilized Blue Phase III

A polymer‐stabilized blue phase (PSBP) III mode device has demonstrated a wide temperature range (> 80 K) of BP III, enhanced dark state level, and hysteresis‐free. At zero electric field, PSBP III exhibits excellent dark state because of no selective Bragg reflection. The strong interactions between the amorphous BP III structure and polymer network, i.e., random morphology of PSBP III implies no preferential orientation or periodicity, enable PSBP III mode device with superior electro‐optical performance and high resistance to aging as well as fast switching.

Effect of Reactive Monomer Concentration on Electro-Optical Properties in Polymer-Stabilized Blue Phase Liquid Crystals with Identical Chiral Dopant Concentrations

The effects of reactive monomer concentration on electro-optical properties were investigated using polymer-stabilized blue phase (PS-BP) liquid crystals (LCs) with different reactive monomer concentrations but identical chiral dopant concentrations. We found that the driving voltage was increased with increase in the reactive monomer concentration, whereas the switching hysteresis and Kerr coefficient were decreased with increase in the reactive monomer concentration in PS-BP LCs with identical chiral dopant concentrations. In addition, we found that the activation energy of electro-optical rising time was increased with increase in the reactive monomer concentration, whereas that of electro-optical decay, time was slightly decreased with increase in the reactive monomer concentration in PS-BP LCs.

Anisotropy of the electro-optic Kerr effect in polymer-stabilized blue phases.

Liquid crystalline polymer stabilized blue phases (PSBPs) are candidate materials for next generation electro-optic switching devices because they form a self-organized three-dimensional periodic structure and exhibit a fast response time of submillisecond order. Considering the crystallographic structures of PSBPs, it is intuitive to believe that the electro-optic effect would depend on the direction of the applied electric field; however, this relationship has not yet been investigated. In this study, we prepared two kinds of samples in which the (110) and (200) planes were oriented parallel to the substrates, and investigated the electro-optic Kerr effect as a field was applied between the two substrates. The two samples exhibited differing behaviors, with the Kerr coefficient of the (110)-oriented sample being larger by 20% than that of the (200)-oriented sample. These results imply that the electro-optic Kerr effect of PSBPs is not isotropic but anisotropic, just like cubic optical crystals.

Hysteresis-free polymer-stabilised blue phase liquid crystals comprising low surface tension monomers

Partial replacement of fluoroacrylates in the monomer composition is able to reduce the free energy of polymer-stabilised blue phase liquid crystal (PSBPLC) due to their low surface tension. The ease of blue phase platelet texture formation is observed under fast cooling and short annealing time before ultraviolet irradiation. The peak driving voltages are dramatically decreased from 9% to 16% in the resulting PSBPLCs. In addition, the hysteresis is completely suppressed in the PSBPLC containing 3FM-M1. The other PSBPLC containing fluoroacrylates retain very small hysteresis (△V < 0.8 V) regardless the fluorine atom numbers. In comparison with current PSBPLCs, the fluoroacrylates serve as mesophase enhancer not only to promote the blue phase formation but also to improve the electro-optical properties.

基于多重掺杂的高科尔常数聚合物稳定蓝相液晶

基于多重掺杂的高科尔常数聚合物稳定蓝相液晶

A giant polymer lattice in a polymer-stabilized blue phase liquid crystal.

Ultrasmall-angle synchrotron X-ray scattering measurements showed that a three-dimensional polymer lattice of a few 100 nm order with body-centered cubic O(8-) symmetry was formed in a polymer-stabilized blue phase liquid crystal. We obtained clear experimental evidence that the polymer chains condensed selectively in the disclinations within the blue phase during photo-polymerization of monomers in the blue phase.

Low-voltage blue phase liquid crystal displays

Polymer-stabilised blue phase liquid crystal displays (PS-BPLCD) based on Kerr effect have become an increasingly important technology for information display applications. In comparison with conventional nematic LC devices, BPLCs exhibit several attractive features, such as sub-millisecond grey-to-grey response time, reasonably wide temperature range, no need for alignment layer, optically isotropic voltage-off state and large cell gap tolerance. However, some technical challenges such as high operation voltage, hysteresis, residual birefringence and relatively low transmittance remain to be overcome before their widespread applications can be realised. Recent progress on BPLC materials and devices has shown great promise. From material aspect, the electro-optical properties of blue phase liquid crystal material system are studied. To realise the electro-optic effect of PS-BPLC, novel device configurations that can dramatically improve the display performances are designed.

Electrically tunable high Q-factor micro-ring resonator based on blue phase liquid crystal cladding.

This work demonstrates an electrically tunable silicon nitride (SiN) micro-ring resonator with polymer-stabilized blue phase liquid crystals (PSBPLCs) cladding. An external vertical electric field is applied to modulate the refractive index of the PSBPLCs by exploiting its fast-response Kerr effect-induced birefringence. The consequent change in the refractive index of the cladding can vary the effective refractive index of the micro-ring resonator and shift the resonant wavelength. Crystalline structures of PSBPLCs with a scale of the order of hundreds of nanometers ensure that the resonator has a very low optical loss. The measured tuning range is 0.45 nm for TM polarized light under an applied voltage of 150V and the corresponding response time is in the sub-millisecond range with a Q-factor of greater than 20,000.

Electro-optic response of polymer-stabilized blue phase liquid crystals

The dynamic response of a polymer-stabilized blue phase liquid crystal (BPLC) is comprised of two distinct processes: Kerr effect-induced local reorientation and electrostriction-induced lattice distortion. A double exponential rise/decay model is proposed to analyze the underlying physical mechanisms. If the electric field is below a critical field (Ec), Kerr effect dominates and the response time is fast. However, when E &amp;gt; Ec electrostriction effect manifests, leading to an increased response time and a noticeable hysteresis. A higher polymer concentration helps suppress electrostriction, but the tradeoff is increased operation voltage. These results provide useful guidelines for future BPLC material and device optimizations.

Fast-Response Liquid Crystal Microlens

Electrically tunable liquid crystal microlenses have attracted strong research attention due to their advantages of tunable focusing, voltage actuation, low power consumption, simple fabrication, compact structure, and good stability. They are expected to be essential optical devices with widespread applications. However, the slow response time of nematic liquid crystal (LC) microlenses has been a significant technical barrier to practical applications and commercialization. LC/polymer composites, consisting of LC and monomer, are an important extension of pure LC systems, which offer more flexibility and much richer functionality than LC alone. Due to the anchoring effect of a polymer network, microlenses, based on LC/polymer composites, have relatively fast response time in comparison with pure nematic LC microlenses. In addition, polymer-stabilized blue phase liquid crystal (PS-BPLC) based on Kerr effect is emerging as a promising candidate for new photonics application. The major attractions of PS-BPLC are submillisecond response time and no need for surface alignment layer. In this paper, we review two types of fast-response microlenses based on LC/polymer composites: polymer dispersed/stabilized nematic LC and polymer-stabilized blue phase LC. Their basic operating principles are introduced and recent progress is reviewed by examples from recent literature. Finally, the major challenges and future perspectives are discussed.

P‐111: Polymer Effect on Polymer‐Stabilized Blue Phase Liquid Crystals

AbstractWe have investigated the polymer effect on the thermal stability and electro‐optical properties of polymer‐stabilized blue phase (PSBP) liquid crystal. The temperature range of polymer stabilized blue phase liquid crystal samples expanded over 54°C including room temperature. The experimental results showed that polymer plays an important role in the thermodynamic stability of blue phase liquid crystals and reducing switching voltage.

Stabilization of cholesteric blue phases using polymerized nanoparticles.

This study explores the roles of UV-polymerizable silicon-based nanoparticles in polymer-stabilized blue phase (PSBP) liquid crystals. Our analysis reveals that the polymerized polymer leads to widening of the temperature range of the blue phase and stabilization of the reflection wavelength against temperature variations. A polymer morphology study of PSBP reveals the polydomain nature of the blue phase. In practical application, the advantage of the low-surface-energy property of the UV-polymerizable silicon-based nanoparticles leads to a significant reduction in switching voltage from 140 to 40V.

Secondary electro-optic effect in liquid crystalline cholesteric blue phases

The electro-optic Kerr effect in cubic blue phase liquid crystals comprises two components with different characteristic response times: one attributed to the primary (purely electro-optic) effect and another attributed to the secondary, or indirect (photoelastic) effect. Through simultaneous measurement of the polarized reflection spectrum and transmitted phase, we show that the contribution of the secondary electro-optic effect can be as large as 20% of the total change in refractive index, and that it is suppressed in the polymer-stabilized blue phase. Our results show the importance of stabilizing the lattice structure to realize blue-phase devices with fast response.

Effect of cyanobiphenyl homologue molecules on electro-optical properties in liquid crystal blue phases and polymer-stabilized blue phases

The effects of cyanobiphenyl (CB) homologue molecules on the electro-optical properties of low-molecular-weight liquid crystal blue phase (BP) and polymer-stabilized BPs are investigated using chiral nematic liquid crystal mixtures that include CB molecules. The driving voltage and switching hysteresis of BPs were found to increase by polymer stabilization of the BP. It was also confirmed that the electro-optical rising time and Kerr coefficient of BPs vary with the molecular parity, as determined by the alkyl chain length of the n-CB homologue molecule dissolved in a chiral nematic liquid crystal mixture. The electro-optical properties of the low-molecular-weight liquid crystal (LC) blue phase and the polymer-stabilized blue phase are investigated using the cyanobiphenyl homologue chiral nematic LC mixtures. It was found that the driving voltage and the switching hysteresis of blue phase were increased by polymer stabilization. Also, it was confirmed that the electro-optical rising time of blue phase was varied with the molecular parity of the n-CB homologue chiral nematic LC mixtures.

The essentials of the Kerr effect for polymer-stabilized blue phase liquid crystal

The essentials of the Kerr effect of the polymer-stabilized blue phase liquid crystal (PS-BPLC) are examined using the director model. The Kerr effect describes that the induced birefringence is proportional to the square of the magnitude of the electric field E. The formula should be corrected when E is large. In contrast, the director model can describe the induced birefringence for any magnitude of E. From the director model, it can be found that the birefringence value essentially has a linear relationship with the averaged direction cosine of the directors with respect to the direction of the electric field.

Electro-Optic Potential of Room and High Temperature Polymer Stabilised Blue Phase Liquid Crystal

In the field of liquid crystals, blue phases (BPs) are one of the most unique and interesting sub-phases. Blue-phase liquid crystal holds the potential to become next-generation display and photonics device because of its sub-millisecond gray-to-gray response time, alignment-layer-free process, optically isotropic dark state, and cell gap insensitivity. The BPLC is a highly chiral liquid crystal system possessing crystal like unit cell structure and exist over a small temperature range (0.5-2 °C) between isotropic and chiral nematic (N*) thermotropic phase. The narrow phase range has been an intrinsic problem for blue phase, and a useful strategy of widening the phase is by adding polymer to form a polymer stabilised blue phase liquid crystal. In this paper, we demonstrate polymer stabilization using two different cases: a room temperature mixture containing E8, PE-5CNF and CPP-3FF, and a high temperature mixture using a single molecule blue phase liquid crystal material, TCB5. Comparison of the polymer stabilization effects on these two cases will be discussed, in the perspective of their potential in electro-optic applications.

The Influence of polymer system on polymer-stabilised blue phase liquid crystals

The influence of polymer system on polymer-stabilised (PS) blue phase (BP) liquid crystal (LC) is investigated. After polymer stabilisation, anchoring energy appears between the polymer network and LC molecules, which is related with the stiffness of the polymer system. As the stiffness of polymer system decreases, the Kerr constant can be improved with the degradation of response time, hysteresis, and residual birefringence. Furthermore, the Kerr constant and response time can be improved simultaneously by polymer system with reactive diluents.