Blue Phase Liquid Crystal Research Articles

Stretchable Blue Phase Liquid Crystal Lasers with Optical Stability Based on Small-Strain Nonlinear 3D Asymmetric Deformation.

Blue phase liquid crystal (BPLC) lasers exhibit exceptional optical quality and tunability to external stimuli, holding significant promise for innovative developments in the field of flexible optoelectronics. However, there remain challenges for BPLC elastomer (BPLCE) lasers in maintaining good optical stability during stretching and varying temperature conditions. In this work, a stretchable laser is developed based on a well-designed BPLCE with a combination of partially and fully crosslinked networks, which can output a single-peak laser under small deformation (44.429nm lasing shift at 32% strain) and a broad-temperature range (from -20 to 100°C). The superior performance can be attributed to the nonlinear 3D asymmetric deformation exhibited by the BPI lattice during stretching, particularly at low deformation rates below 40% strain, which effectively maintains the stability of the body-centered cubic structure (with the maximum strain of this BPLCE up to 220%). Moreover, the BPLCE exhibits excellent thermal stability over a temperature range from -180 to 70°C with a stopband shift of less than ±10nm. As a proof-of-concept, the application of BPLCE laser for morphology sensing and 3D mechanical perception is demonstrated, which paves the way for potential applications of flexible optoelectronics.

Independent Multiple‐Optical‐Parameter Modulations Enabled by Manipulating the Separate Levels of a Hierarchical Structure

AbstractOwing to their intrinsic multiple physical dimensions and high parallelism, photons are superior to electrons when they act as information carriers. The independent and dynamic spatial modulations of multiple optical parameters of light are highly pursued in vital fields such as supercomputing, constellation satellite and optical communications, virtual/augmented reality, and holographic displays. To date, it is still challenging to accomplish this urgent task with a single element. Here, multiple optical parameter modulations are carried out via manipulation of the separate levels of a hierarchical structure. Photopatterning, light irradiation, and an electric field are adopted to regulate the patterned crystallizations, lattice constants, and tilt angles of blue‐phase liquid crystals (BPLCs). As the optical parameters are associated with the individual structural features, it enables binary reflectance and spatial geometric phase modulations, reversable wavelength shifting, and continuous reflectance variations with excellent independency. This work unlocks the multi‐degree modulation of light and addresses the miniaturization, integration, and dynamic and multifunctional tendencies of rapidly growing optical informatics. Owing to its merits of omnidirectional, independent control, and dynamic response, it may dramatically upgrade the performance of existing optics.

Nematic host and alignment layer dependence on monodomain formation in the liquid crystal blue phase

Blue phases (BPs) of liquid crystals are highly valued in electro-optics for their fast, polarization-independent response and the advantage of not requiring alignment layers. While BP lattices do not need to be aligned to substrates, doing so can improve their electro-optic performance. Traditionally, rubbed polyimide films have been the preferred method for inducing monodomains in BPs. This study, using polarized optical microscopy, explores various BP compositions with different nematic hosts, chiral dopant concentrations, and alignment layer combinations, including polyimide, surfactants, and obliquely evaporated SiOx. The results show that while rubbed polyimide is effective for many BP compositions, it is not always the optimal choice for inducing monodomains. The research highlights that inorganic alignment methods can be more effective for BP compositions consisting of specific nematic hosts.

Photopatterned Anchoring Stabilizing Monodomain Blue Phases.

Blue phase liquid crystals (BPLCs) are chiral self-assembled three-dimensional (3D) periodic structures which have attracted a lot of attention due to their electro-optical properties, relevant for tunable soft photonic crystals and fast-response displays. However, to realize this application potential, controlling the BPLC alignment at the surfaces is crucial, and one way to obtain the desired alignment is by photoalignment patterning. In this article, monodomain BPLC samples with controlled orientation are achieved by imposing different alignment patterns that have a periodicity that is compatible with the size of the BPLC unit cell, using two-step photoalignment with polarized ultraviolet (UV) light. Experiments are complemented by numerical simulations to design striped surface alignment patterns, which induce specific director orientations on the boundary layer of the confined BPLC. By designing the patterns and matching the periodicity to a specific BP material, we can control the orientation of the blue phase unit cell lattice in the sample, including the azimuthal angle. The orientation is measured by the Kossel patterns and matches the optimal configuration predicted by stability analysis using Landau-de Gennes free energy modeling. The detailed structure and reduced symmetry of the BP near the surface are investigated, and the corresponding (meta)stable structures are demonstrated. Overall, we demonstrate that two-step photoalignment patterning is a reliable, relatively simple, and reconfigurable method to achieve a high-quality monodomain BP with controlled and tunable crystalline orientation.

Spatiotemporal Programmability of 3D Chiral Color Units Driven by Ink Spontaneous Diffusion toward Customized Printing.

Blue phase liquid crystals (BPLCs) have exhibited promising applications in 3D flexible displays due to their molecular-level self-assembled chiral structures, fast response, and tunable polarized colors. However, there remain challenges for spatiotemporal programming of 3D chiral color units for BPLC dynamic patterning. Herein, the programmable temporal evolution of micrometer-scale color units and spatial configuration switch of chiral modes are achieved by spontaneous ink diffusion-driven asymmetric lattice deformation in dual-chiral polymer-templated blue phases. Custom-printed colorful patterns are designed by machine learning-assisted parameter optimization, which displays programmable multidimensional encrypted information that incorporates temporal evolving colors (wavelength), spatial distribution (depth), chiral modes (L/R). The quantitative relationship between ink diffusion kinetics and blue-phase dynamic 3D structural optics is established by in situ characterization, finite element analysis, and mathematical geometry modeling. This work provides insights into the microgeometric manipulation of 3D chiral color of BPLCs in the application of information security and self-adaptive indicators.

In Situ Characterization of Thermal‐Induced Evolution of Structure/Optical Properties of Heterogeneous 3D Chiral Soft Photonic Crystal Polymer

AbstractPolymer stabilized blue phase (PSBP) liquid crystal has aroused wide attention due to its broad temperature range and potential applications in flexible display, multi‐mode monitor, and mirrorless laser based on its well‐compatible stability and multi‐responsiveness, such as electricity, humidity, and temperature. Temperature produces an important effect on the structure/optical properties of PSBP, but there lack of detailed investigation on thermal‐induced deformation and its influence on the optical performance of PSBP. Here, the thermal‐induced evolution of structure/optical properties of PSBP with different polymer content is in situ characterized by variable‐temperature ultra‐small‐angle X‐ray diffraction, Kossel diffraction, and polarized optical microscopy. A restricted deformation of PSBP cubic lattice is revealed by the shift of reflective wavelength and evolution of Kossel diagrams, which is mainly attributed to the thermal‐induced phase transition/separation of non‐polymerized components. The thermal stability of PSBP is improved by increased polymer content based on the limited deformation ability. This work is significant for the design of novel functional material, which paves the way for the preparation of photonic crystal soft materials with high stability and optical quality.

Directed crystalline symmetry transformation of blue-phase liquid crystals by reverse electrostriction

Soft-matter-based photonic crystals like blue-phase liquid crystals (BPLC) have potential applications in wide-ranging photonic and bio-chemical systems. To date, however, there are limitations in the fabrication of large monocrystalline BPLCs. Traditional crystal-growth process involves the transition from a high-temperature disordered phase to an ordered (blue) phase and is generally slow (takes hours) with limited achievable lattice structures, and efforts to improve molecular alignment through post-crystallization field application typically prove ineffective. Here we report a systematic study on the molecular self-assembly dynamics of BPLC starting from a highly ordered phase in which all molecules are unidirectionally aligned by a strong electric field. We have discovered that, near the high-temperature end of the blue phase, if the applied field strength is then switched to an intermediate level or simply turned off, large-area monocrystalline BPLCs of various symmetries (tetragonal, orthorhombic, cubic) can be formed in minutes. Subsequent temperature tuning of the single crystal at a fixed applied field allows access to different lattice parameters and the formation of never-before-seen monoclinic structures. The formed crystals remain stable upon field removal. The diversity of stable monocrystalline BPLCs with widely tunable crystalline symmetries, band structures, and optical dispersions will significantly improve and expand their application potentials.

A Halogen-Bonded Fluorescent Molecular Photoswitch: Transition from 3D Cubic Lattice to 1D Helical Superstructure for Polarization Inversion of Circularly Polarized Luminescence.

The fabrication of materials that can switch between circularly polarized luminescence (CPL) signals is both essential and challenging. Here, two new halogen-bonded fluorescent molecular photoswitches, namely, HB-switch 1 and HB-switch 2, containing α-cyano-substituted diarylethene compounds with different end groups were developed. Upon exposure to specific UV or visible light wavelengths, they exhibited controllable and reversible Z/E photoisomerization. When these switches were integrated into blue-phase liquid crystals (BPLCs), the temperature range of BP significantly expanded. Notably, the BP system incorporating HB-switch 1 exclusively achieved reversible polarization inversion of CPL signals under irradiation with specific UV/Visible light and during cooling/heating. The photo/thermal dual-response behavior of the CPL signals can be attributed to the phase transition from a high-symmetry 3D BP Icubic lattice to a low-symmetry 1D helical superstructure induced by the Z/E photoisomerization of HB-switch 1 and temperature changes. This study underscores the significance of employing halogen-bond assembly strategies to design materials with switchable CPL signals, opening new possibilities for CPL-active systems.

A Halogen‐Bonded Fluorescent Molecular Photoswitch: Transition from 3D Cubic Lattice to 1D Helical Superstructure for Polarization Inversion of Circularly Polarized Luminescence

AbstractThe fabrication of materials that can switch between circularly polarized luminescence (CPL) signals is both essential and challenging. Here, two new halogen‐bonded fluorescent molecular photoswitches, namely, HB‐switch 1 and HB‐switch 2, containing α‐cyano‐substituted diarylethene compounds with different end groups were developed. Upon exposure to specific UV or visible light wavelengths, they exhibited controllable and reversible Z/E photoisomerization. When these switches were integrated into blue‐phase liquid crystals (BPLCs), the temperature range of BP significantly expanded. Notably, the BP system incorporating HB‐switch 1 exclusively achieved reversible polarization inversion of CPL signals under irradiation with specific UV/Visible light and during cooling/heating. The photo/thermal dual‐response behavior of the CPL signals can be attributed to the phase transition from a high‐symmetry 3D BP Icubic lattice to a low‐symmetry 1D helical superstructure induced by the Z/E photoisomerization of HB‐switch 1 and temperature changes. This study underscores the significance of employing halogen‐bond assembly strategies to design materials with switchable CPL signals, opening new possibilities for CPL‐active systems.

When quantum dots meet blue phase liquid crystal elastomers: visualized full-color and mechanically-switchable circularly polarized luminescence

Polymer-based circularly polarized luminescence (CPL) materials with the advantage of diversified structure, easy fabrication, high thermal stability, and tunable properties have garnered considerable attention. However, adequate and precise tuning over CPL in polymer-based materials remains challenging due to the difficulty in regulating chiral structures. Herein, visualized full-color CPL is achieved by doping red, green, and blue quantum dots (QDs) into reconfigurable blue phase liquid crystal elastomers (BPLCEs). In contrast to the CPL signal observed in cholesteric liquid crystal elastomers (CLCEs), the chiral 3D cubic superstructure of BPLCEs induces an opposite CPL signal. Notably, this effect is entirely independent of photonic bandgaps (PBGs) and results in a high glum value, even without matching between PBGs and the emission bands of QDs. Meanwhile, the lattice structure of the BPLCEs can be reversibly switched via mechanical stretching force, inducing on-off switching of the CPL signals, and these variations can be further fixed using dynamic disulfide bonds in the BPLCEs. Moreover, the smart polymer-based CPL systems using the BPLCEs for anti-counterfeiting and information encryption have been demonstrated, suggesting the great potential of the BPLCEs-based CPL active materials.

All-optical 3D blue phase photonic crystal switch with photosensitive dopants

Blue phase (BP) liquid crystals (LC) have lately become the focus of extensive research due to their peculiar properties and structure. BPs exhibit a highly organized 3D structure with a lattice period in the hundreds of nm. Owing to such structure, BPs are regarded as 3D photonic crystals. The unique properties of this complex LC phase are achieved by the self-assembly of the LC molecules into periodic cubic structures, producing bright selective Bragg reflections. Novel applications involving 3D photonic crystals would certainly benefit from enhanced ground-breaking functionalities. However, the use of BPs as 3D has been traditionally curtailed by the BP crystals trend to grow as random polycrystals, making it difficult to develop practical BP-based photonic devices. The possibility of generating mm-sized BP monocrystals was recently demonstrated. However, besides increasing the scarce number of 3D photonic structural materials, their applications as 3D photonic crystals do not show apparent advantages over other solid materials or metamaterials. Having a tunable BP monocrystal, where crystals could be switched, modulating simultaneously some of their properties as 3D photonic crystals, they would constitute a new family of materials with superior performance to other existing materials, opening up a plethora of new applications. In this work, an all-optical switchable 3D photonic crystal based on BPs doped with tailored photoactive molecules is demonstrated. Two switching modes have been achieved, one where the BP reversibly transitions between two BP phases, BPI and BPII, (two different cubic crystal systems) while maintaining the monocrystallinity of the whole system. The second mode, again reversible, switches between BPI and isotropic state. None of these modes are related to the regular thermal transitions between LC phases; switching is triggered by light pulses of different wavelengths. This all-optical approach allows for a seamless fast remotely controlled optical switch between two 3D photonic crystals in different cubic crystal systems and between a photonic crystal and an isotropic matrix. Applications of switchable BPs for adaptive optics systems or photonic integrated circuits would make great advances using 3D photonic crystal switches. All-optical photonic systems such as these hold great promise for the development of tunable and efficient photonic devices such as dynamic optical filters and sensors, as they enable light-driven modulation and sensing applications with unprecedented versatility.

Effect of High-Index Nanoparticles on the Emission Properties of a Dye-Doped Blue Phase Liquid Crystal

Effect of High-Index Nanoparticles on the Emission Properties of a Dye-Doped Blue Phase Liquid Crystal

Chiral monomer template for designing Low-Driving-Field blue phase liquid crystals

Blue phase liquid crystals (BPLC) are known to be useful for various non-trivial applications due to their nanoscale self-assembled cubic crystalline structures. Even though the BPLC exhibits an efficient optically isotropic phase due to the double helical confinement of liquid crystal (LC) molecules within a few hundred-nanometer range, this hinders the orientation of LC molecules along the applied field direction. Consequently, the BPLC demands larger driving fields to operate, degrading the device’s performance in real-world applications. In this context, we provide a chiral monomer template for BPLC that decreases the driving field by 52 % while the electro-optical responses remain unaffected. Furthermore, our approach provides higher thermal stability, with a broader BPLC phase range (42 °C), including near ambient temperature. As this approach potentially overcomes the fundamental challenges of BPLC, the proposed system could be useful for next-generation display devices.

Liquid crystal-induced tunable circular dichroism in CdSe and ZnSe nanoplatelets

Induced circular dichroism in CdSe and ZnSe nanoplatelets (NPLs) was demonstrated using chiral thermotropic liquid crystals (LCs). Firstly, NPLs were easily dispersed in cholesteryl oleyl carbonate (COC) LC via a simple intercalation chemistry-based approach. Extensive circular dichroism (CD) studies showed remarkably strong and reversible chiroptical properties for these composites as a function of temperature. NPL-COC composites displayed strong exciton-induced CD as well as high anisotropy g-factor values (in the case of CdSe NPLs). Secondly, induced chirality in CdSe NPLs was also demonstrated using right-handed (RH) and left-handed (LH) blue phase LCs. LC-induced chirality in nanoparticles was corroborated by theoretical studies which revealed coupling between the chiral molecular excitons and nonchiral nanocrystals. The temperature-tunability is a useful tool to switch the chirality on/off. This study presents an alternative approach to realize exciton-induced tunable circular dichroism in nanomaterials.

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.

Anisotropic crystal growth in blue phase I transitioned from a uniformly oriented cholesteric phase.

Phase transitions in blue phase liquid crystals (BPLCs) have attracted significant attention from the technical perspective of BP orientation control and the theoretical perspective of analogs with crystalline solids. The phase transition phenomena in BPs significantly depend on the phase state before the transition. In this study, we focused on the cholesteric (Ch)-BPI phase transition and found that BPI crystals exhibited a square shape upon the phase transition from the uniformly oriented Ch phase to the BPI phase. This square crystal shape was common across three BPLC materials with different elastic constants, and the shape reflected the crystal axis. The in-plane crystal orientation correlates with the easy axis on the substrate surface, suggesting that the [011] axis tends to coincide with the easy axis. However, the easy axis has little effect on the crystal growth rate. Furthermore, scratches on the substrate surface promoted nucleation. Based on this behavior, it was demonstrated that the nucleation position and density could be controlled by intentionally disturbing the Ch orientation by locally changing the easy axis using photoalignment. This study focused on the anisotropic crystal growth of BPI, providing interesting insights into LC phase transitions and soft matter crystal growth. In addition, it offers techniques for the fabrication of large BPI crystals, contributing to the enhanced electrical and optical performances of BPLC devices.

Characterization and mechanism investigation of layer-by-layer phase transition process in blue phase liquid crystals

Characterization and mechanism investigation of layer-by-layer phase transition process in blue phase liquid crystals

A blue phase liquid crystal film based on an interpenetrating network and its sensitive humidity response performance

A humidity-responsive blue phase liquid crystal polymer film (alkalized-acrylic-BP) based on an interpenetrating polymer system has been fabricated.

Spontaneous formation of liquid-crystalline nuclei in blue-phase liquid crystals based on different chirality

The self-assembly of three-dimensional nanostructures of blue-phase liquid crystals is becoming the spotlight of soft matter research and has potential applications in photonic crystals, sensors, electro-optic devices, and others.

Effect of blue-phase liquid crystals on the fluorescence properties of aggregation-induced emissive molecules

Effect of blue-phase liquid crystals on the fluorescence properties of aggregation-induced emissive molecules