Liquid Crystal Phase Research Articles

Concentration-Dependent Control of the Band Gap Energy of a Low-Dimensional Lepidocrocite Titanate.

Recently, we reported on the simple, scalable synthesis of quantum-confined one-dimensional (1D) lepidocrocite titanate nanofilaments (1DLs). Herein, we show, using solid-state UV-vis spectroscopy, that reducing the concentration of aqueous 1DL colloidal suspensions from 40 to 0.01 g/L increases the band gap energy and light absorption onset of dried filtered films from ≈3.5 to ≈4.5 eV. This range is ascribed to quantum confinement as the system transitions from two-dimensional (2D) into 1D with dilution. It is only after the colloidal suspensions are dried and the 1DLs start to self-assemble into ribbons and sheets that the band gap values change. This self-assembly is manifested in the X-ray diffraction patterns and the emergence of a Raman band characteristic of 2D lepidocrocite titanates. In colloidal form, 1DLs exhibit a lyotropic liquid crystal phase with a critical concentration of between 10 and 1 g/L. Additionally, the Beer-Lambert law applies with a mass absorbance coefficient of 2 ± 0.4 Lg-1 cm-1. The optical absorbance edges of the colloidal suspensions are not a function of concentration. The experimental findings are theoretically supported by density functional theory calculations of the Raman vibrational modes and electronic band structures of the 1D and 2D lepidocrocite titanate atomic structures.

Panchromatic Absorption of Unsymmetrical Donor-Acceptor Dyes Based on a Meta-conjugated 1,3,5-Heteroaryltriazine Core.

Attachment of three different heterocycles with electron donor or acceptor character to a central 1,3,5-triazine core generates readily soluble side-chain free dyes with two displaying soft crystalline mesomorphism and one displaying a nematic liquid crystal phase as confirmed by polarized optical microscopy, calorimetry, gravimetric analysis, and powder X-ray diffraction. Equally intriguing is the dyes' relatively strong electronic communication between donor and acceptor subchromophores that are meta-conjugated to one another, which is experimentally observed as a broad intramolecular charge-transfer absorption that can extend over 100 nm past the most intense absorption event and is computationally confirmed through density functional theory (DFT) evaluations of the molecular ground- and excited-state properties. This molecular design permits the preparation of dyes with panchromatic absorption not just based on the additive absorption of individual subchromophores.

Cholesteric liquid crystal mixtures for the switchable smart windows and light shutters: Electro-optical and dielectric behaviour

Abstract Cholesteric liquid crystal (CLC) mixtures with variable pitch lengths were prepared for the electrical switchable smart window and light shutter applications by taking varied concentrations (2.6, 3.0, 4.0, and 5.0 wt%) of chiral dopant (R1011) having helical twisting power (HTP) 37.6 μm−1 and nematic E7 liquid crystal (LC). The morphological and electro-optical analysis of these CLC mixtures filled in 10µm thick cells were observed and reported herein, the switching of initial planar (P) and initial focal conic (FC) to homeotropic (H) states as well as vice-versa. The operating voltage of the 2.6 wt% of chiral doped CLC cell was relatively lower among all the sample cells compared with other concentrations. The maximum contrast ratio (CR) was observed for 5.0 wt% chiral doped CLC cell with initial planar state. However, the best CR was observed in 2.6wt% CLC cell with initial FC state. The comparative macroscopic views of the P, FC, and H states in the OFF and ON conditions of applied voltage for prepared CLC cells were observed for transparent and opaque states. Further, UV-visible spectroscopy was performed in the P, FC, and H states under the application of an externally applied field to observe the absorbance and band gap behavior of the fabricated CLC cells. Additionally, chiral concentration-dependent dielectric parameters with variable frequency in initial P and FC states of the fabricated cells were also reported. The temperature-dependent phase behavior of all the prepared cells exhibited a slight decrease in the isotropic phase of LC due to the doping of chiral dopants.

Ferroelectric Nematic Liquid Crystals Showing High Birefringence.

High birefringence nematic liquid crystals are particularly demanded for adaptive optics applications in the infrared spectrum because it enable a thinner cell gap for achieving fast response time and improved diffraction efficiency. The emerging ferroelectric nematic liquid crystals have attracted widespread interest in soft matter due to their unique combination of ferroelectricity and fluidity. However, the birefringence, which is one of the most important optical parameters in electro-optic devices, is not large enough (<0.25) in most ferroelectric nematic materials. Here, a polar liquid crystal molecule library containing more than 60 molecules with a highly rigid and fluorinated nature is developed. The introduction of triple bonds constructs a long π-electron conjugated mesogen skeleton, significantly improving the birefringence of polar liquid crystal phases. The birefringence and dispersion properties are systematically studied, demonstrating a strong dependence on chemical structures and the type of polar phases. Furthermore, through multi-component mixing, polar liquid crystal mixtures with ultra-wide temperature range and excellent stability at or near room temperature are obtained. They possess much higher birefringence than the existing ferroelectric liquid crystal materials. The unique combination of high birefringence and fluidic ferroelectricity is expected to promote the application of polar liquid crystals in electro-optic technologies.

Phosphorescent Liquid Crystalline Polymer-based Circularly Polarized Luminescence Optical Waveguides for Enhanced Photonic Signal Processing and Information Encryption.

Efficient circularly polarized luminescence (CPL) optical waveguides have significant potential for advancing photonic and optoelectronic devices. However, the development of CPL optical waveguides materials (OWMs) with low optical loss coefficient remains a considerable challenge. To overcome this, we design and synthesize CPL OWMs based on room-temperature phosphorescent liquid crystalline polymers (LCPs). Experimental results demonstrate that these LCPs exhibit a nematic liquid crystal phase and a phosphorescence lifetime of approximately 0.145 ms. By introducing a chiral dopant, we induce a chiral arrangement in the LCPs, followed by crosslinking via photo-cycloaddition and removal of the chiral dopants through solvent soaking. The resulting polymers exhibit stable solvent resistance and highly efficient circularly polarized phosphorescence (CPP) properties, with dissymmetric factors (gRTP) in the range of 0.16 to 0.17. Notably, the CPP-active OWMs exhibit efficient circularly polarized photonic signal waveguiding, with an optical loss coefficient of approximately 0.175 dB/mm. Ultimately, these CPP-active OWMs are sucessfully applied in information encryption, decryption, and optical switching, paving the way for advanced photonic and optoelectronic devices.

Phosphorescent Liquid Crystalline Polymer‐based Circularly Polarized Luminescence Optical Waveguides for Enhanced Photonic Signal Processing and Information Encryption

Efficient circularly polarized luminescence (CPL) optical waveguides have significant potential for advancing photonic and optoelectronic devices. However, the development of CPL optical waveguides materials (OWMs) with low optical loss coefficient remains a considerable challenge. To overcome this, we design and synthesize CPL OWMs based on room‐temperature phosphorescent liquid crystalline polymers (LCPs). Experimental results demonstrate that these LCPs exhibit a nematic liquid crystal phase and a phosphorescence lifetime of approximately 0.145 ms. By introducing a chiral dopant, we induce a chiral arrangement in the LCPs, followed by crosslinking via photo‐cycloaddition and removal of the chiral dopants through solvent soaking. The resulting polymers exhibit stable solvent resistance and highly efficient circularly polarized phosphorescence (CPP) properties, with dissymmetric factors (gRTP) in the range of 0.16 to 0.17. Notably, the CPP‐active OWMs exhibit efficient circularly polarized photonic signal waveguiding, with an optical loss coefficient of approximately 0.175 dB/mm. Ultimately, these CPP‐active OWMs are sucessfully applied in information encryption, decryption, and optical switching, paving the way for advanced photonic and optoelectronic devices.

Freely suspended nematic and smectic films and free-standing smectic filaments in the ferroelectric nematic realm.

We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic (NF) phase and from the recently discovered polar, lamellar SmZA and SmAF phases. The NF films display two-dimensional, smectic-like parabolic focal conic textures comprising director/polarization bend that are a manifestation of the electrostatic suppression of director splay in the film plane. In the SmZA and SmAF phases, the smectic layers orient preferentially normal to the film surfaces, a condition never found in typical thermotropic or lyotropic lamellar LC phases, with the SmZA films exhibiting focal-conic fan textures mimicking the appearance of typical smectics in glass cells when the layers are oriented normal to the plates, and the SmAF films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The SmAF phase can also be drawn into thin filaments, in which X-ray scattering reveals that the smectic layer planes are normal to the filament axis. Remarkably, the filaments are mechanically stable even if they break, forming free-standing, fluid filaments supported only at one end. The unique architectures of these films and filaments are stabilized by the electrostatic self-interaction of the liquid crystal polarization field, which enables the formation of confined, fluid structures that are fundamentally different from those of their counterparts made using previously known liquid crystal phases.

Research on pointing accuracy of liquid crystal phase array based on the variable period grating method

Research on pointing accuracy of liquid crystal phase array based on the variable period grating method

Birefringence inversion in liquid crystalline poly(substituted methylene)s bearing side-on mesogens

Liquid crystalline poly(substituted methylene)s (PMs) with side-on mesogens exhibit reversible birefringence (Δn) inversion during liquid crystal (LC)-to-LC phase transitions as the temperature increases. The low-temperature LC phase exhibits a positive...

BIOPHYSICAL INVESTIGATION OF MOLECULAR INTERACTIONS BETWEEN ALLIIN AND ANIONIC DMPG MODEL MEMBRANE: AN FTIR STUDY

Garlic, which contains bioactive compound alliin, is a medicinal herb that has been traditionally utilized for its therapeutic properties against a range of illnesses. Our aim is to investigate the interactions between alliin and anionic dimyristoyl phosphatidylglycerol (DMPG) multilamellar vesicles (MLVs) at various temperatures and alliin concentrations (1, 3, 6 and 9 mol%) using Fourier transform infrared (FTIR) spectroscopy. The PerkinElmer Frontier spectrometer was used to collect spectra within the region of 4000-1000 cm-1. The specimens were subjected to scanning within a temperature range of 0 to 40 °C using the Specac temperature control device. The analyses were conducted utilizing the Spectrum v10.3.7 program. By introducing both low and high concentrations of alliin to DMPG MLVs, the wavenumber values of the CH2 antisymmetric stretching band decreased, while the bandwidth values increased, both in the gel and liquid crystal phases. During the gel phase, the presence of alliin resulted in a downward shift of the C=O stretching bands' wavenumber values. Opposite evidence occurred in the liquid crystal phase. The wavenumber values of the PO2- antisymmetric stretching band exhibited a shift towards lower values both in the gel and liquid crystal phases. In the present study, we investigated the biophysical effects of alliin on DMPG model membranes using parameters such as lipid order, dynamics and hydrogen bonding ability. The addition of alliin altered the physical characteristics of the DMPG MLVs by ordering the system, enhancing its dynamics, and promoting hydrogen bond interactions between the phosphate group of DMPG and alliin or water molecules, both in the gel and liquid crystalline phases. Moreover, alliin enhanced the strength of hydrogen bonding in proximity to carbonyl groups in the gel phase.

A Self-Assembled Periodic Nanoporous Framework in Aqueous Solutions of the DNA Tetramer GCCG.

The collective behavior of the shortest DNA oligomers in high concentration aqueous solutions is an unexplored frontier of DNA science and technology. Here we broaden the realm of DNA nanoscience by demonstrating that single-component aqueous solutions of the DNA 4-base oligomer GCCG can spontaneously organize into three-dimensional (3D) periodic mesoscale frameworks. This oligomer can form B-type double helices by Watson-Crick (WC) pairing into tiled brickwork-like duplex strands, which arrange into mutually parallel arrays and form the nematic and columnar liquid crystal phases, as is typical for long WC chains. However, at DNA concentrations above 400 mg/mL, these solutions nucleate and grow an additional mesoscale framework phase, comprising a periodic network on a three-dimensional body-centered cubic (BCC) lattice. This lattice is an array of nodes (valence-8, each formed by a pair of quadruplexes of GCCG terminal Gs), connected with a separation of 6.6 nm by struts (6-GCCG-long WC duplexes). This 3D-ordered DNA framework is of low density (DNA volume fraction ∼0.2), but due to its 3D crystal structure, it is osmotically incompressible over its phase range. Atomistic simulations confirm the stability of such structures, which promise to form the basis of families of simply and inexpensively made nanoscale frameworks for templating and selection applications.

Marangoni flow across different phases in cyanobiphenyl liquid crystals under temperature gradient

ABSTRACT Marangoni flows driven by temperature gradient in two-phase coexisting states are investigated in this study, using several liquid crystals of the cyanobiphenyl (CB) series. The flow field is measured using the fluorescence photo-bleaching method in sandwich cells, and the characteristic flow is observed near the air interface in all samples. The flow direction is from the isotropic phase to the nematic phase in 5CB and 6CB and from the nematic to the smectic phase in 8CB, which is the case for the three different coating materials of the cell substrates. However, the flow direction observed in 7CB and 8CB changes depending on the coating material in the coexisting state of the nematic and isotropic phases. These results can be explained by the temperature dependence of surface tension γ and the air-interface shape l s near phase-transition temperatures.

Liquid Crystal/Carbon Nanotube/Polyaniline Composites and Their Coating Orientation Patterning Applications

In this work, a coating method was used to prepare a liquid crystal physical gel with a high orientation of liquid crystal molecules, excellent electrical conductivity, and mechanical stability. The liquid crystal matrix used was nematic phase liquid crystal (5CB), the gel factor was polyvinyl alcohol (PVA), and the conductive filler was carbon nanotubes/polyaniline (CNT/PANI). Chemical in situ polymerization was used to create CNT/PANI composites, wherein polyaniline encapsulates the carbon nanotubes to enhance their dispersion. At 4 mm/s, 7.2 N of coating pressure, and 72 s of interval duration, the shear flow-induced orientation was achieved. The consistent and large-area orientation of the liquid crystal molecules was realized and the orientation direction of the liquid crystal molecules was parallel to the coating direction. Additionally, a type of stress sensor assembly based on multiple coating demonstrated a good sensor performance in the 90° bending test and high sensitivity in the 20% tensile test, with a sensor sensitivity of 23.25. Regarding the use of liquid crystal materials in flexible electronic devices, it is quite important.

Influence of an Imposed Network on One- and Three-Dimensional Photonic Liquid Crystal Structures through the Polymer Template Technique.

We describe the first investigations on the influence of an imposed network on the photonic band gap (PBG) structure of the liquid crystal (LC) phase through the polymer template technique. The technique consists of using a cholesteric (Ch) phase as a base for photopolymerizing a difunctional monomer, which is then removed after polymerization, leaving only the polymer scaffold template. The templated structure obtained is utilized to adjust the PBG structure of the filled LC material, exhibiting both a one-dimensional PBG (Ch phase) and a three-dimensional PBG structure (TGBC* phase with smectic C* blocks). Selective reflection measurements indicate that the imprint polymer network of the template impacts the pitch of the Ch and TGBC* phases. The absorption peaks are visible because of two distinct twisted arrangements, one originating from the template and the other from the refilled chiral substance. In the templated cell, the central wavelength (λmin) of PBG of the refilled sample red-shifts, as well as the width of the PBG gets enhanced compared to that for the sample in the regular (nontemplated) cell. For example, in the TGBC* phase, the λmin value red-shifts by 369 nm, and the width of the PBG enlarges by 50%. Additionally, the lattice spacing arising due to the periodicity of the SmC* helix in 2-dimension in the TGBC* phase gets enhanced. These findings demonstrate the polymer template method's effectiveness in tuning the mesophase's PBG in all three dimensions.

The Role of Thermotropic Liquid Crystals in the Detection of Gases that Adversely Affect the Nervous System

In this study, the aim was to develop an innovative and user-friendly sensor capable of quickly detecting the gases phenol, toluene, and 1,2-dichloropropane, which negatively affect brain functions when inhaled over extended periods. To achieve this, the thermotropic phase of liquid crystals, which possess thermotropic and lyotropic phases, was used, and a thermotropic cholesteric liquid crystal(CHLC) sample was formulized. The changes occurring in the presence of these gases were examined optically. In this context, the thermotropic ChLC sample, composed of E7 thermotropic liquid crystal and a chiral mixture made from chiral dopants CB15, R1011, and R811, was placed into a cell created using the sandwich method with glass surfaces modified with lecithin. The mentioned gases, evaporated at different temperatures, were introduced into the cells containing the liquid crystal sample over varying durations, and the resulting changes in the wavelength of the liquid crystal were analyzed. Thus, it was demonstrated that these gases, which have a detrimental impact on human health, can be detected at the lowest concentration levels using a sensor containing thermotropic liquid crystal.

Topologically Protected Vortex Knots in an Experimentally Realizable System.

Ordered media often support vortex structures with intriguing topological properties. Here, we investigate non-Abelian vortices in tetrahedral order using the mathematical formalism of colored links. Due to the generality of our methods, the results apply to all physical systems governed by tetrahedral order, such as the cyclic phase of spin-2 Bose-Einstein condensates and the tetrahedratic phase of bent-core nematic liquid crystals. Using these vortices, we construct topologically protected knots in the sense that they cannot decay into unlinked simple loop defects through vortex crossings and reconnections without destroying the phase. The discovered structures are the first examples of knots bearing such topological protection in a known experimentally realizable system.

Highly conductive broadband transparent DMSO-doped PEDOT: PSS electrodes.

The conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) is considered as a flexible electrode material that can replace traditional electrodes. However, its performance optimization, practical application, and related research are primarily focused on a single band. In this study, we designed and prepared a broadband transparent electrode with a conductivity of up to 1300 S cm-1 based on dimethyl sulfoxide (DMSO)-doped PEDOT: PSS. The as-fabricated PEDOT: PSS electrode achieved high transmittance in a wide range from a visible to terahertz band. The physical mechanism of its high conductivity and broadband transparency is studied by using a first-principle calculation. Furthermore, the transparent electrode exhibited excellent stability after 100,000 cycles of electrical cycling and 200°C of heating. Based on the transparent electrode, we fabricated a liquid crystal phase shifter with an extended operating range, showing its efficient driving performance as an electrode. The characterization and optimization of the properties of PEDOT: PSS in this work provide guidance for the application of PEDOT: PSS in broadband optical devices.

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.

Development of a Spatial Resolution-Enhanced Digital-Hologram Microscope With a Liquid Crystal Phase Modulator

Development of a Spatial Resolution-Enhanced Digital-Hologram Microscope With a Liquid Crystal Phase Modulator