Liquid Crystal Materials Research Articles

Constructing a cellulose based chiral liquid crystal film with high flexibility, water resistance, and optical property

Cellulose nanocrystal (CNC) derived from cellulose can form a liquid crystal film with bright structural color by evaporative-induced self-assembly (EISA). As a new class of photonic liquid crystals material, it has attracted much attention because of its intrinsic unique structural characteristics and excellent optical properties. However, the brittleness and water sensitivity of CNC film have hindered its practical application. Herein, multiple cross-linked networks CNC/(polyethylene glycol diacrylate:polyethylene oxide) (PEGDA:PEO) composite film was prepared through EISA and UV irradiation strategies. The as-prepared film exhibits high-flexibility with a fracture strain of up to 36.40 % and strong water resistance, with water absorption at an equilibrium of only 17.41 %. Moreover, the film retains its structural color in aqueous solution for a long time due to its water stability. The outstanding flexibility and water resistance of CNC composite film are attributed to multiple crosslinked networks (i.e. PEGDA, PEO, and PEDGA-PEO networks), which endow the film with excellent stress dispersion and transferability when stretched and limit film swelling in water without affecting chiral nematic structures of CNC. Overall, this work provides a promising strategy to prepare CNC-based film with high-flexibility, water resistance, and optical property for applications like decoration, sensor, and anti-counterfeiting.

Multi-stable dye-doped dual-frequency twisted nematic liquid crystal smart window.

In this study, a novel, to the best of our knowledge, dye-doped dual-frequency liquid crystal multi-stable smart window is proposed. A chiral dopant with appropriate content was introduced into dye-doped dual-frequency liquid crystals to achieve an initial 180° twisted state. These liquid crystals can be switched to a nematic phase or a 360° twisted state by controlling the magnitude and frequency of the applied voltage. These nematic phase and 360° twisted states can exist stably for a long time because of the backflow effect and the anisotropic nature of the dual-frequency liquid crystal material. Due to the optical waveguide effect of dye-doped liquid crystals in the long-pitch state, the transmittance was different in nematic phase, 180°, and 360° twisted three zero-field stabilized absorption states. Finally, a multi-stable smart window is developed to switch between three zero-field stabilized absorption and scattering states.

Indium tin oxide nanoparticles induced molecular rearrangement in nematic liquid crystal material

In the present article, we report the influence of indium tin oxide (ITO) nanoparticles (NPs) on the macroscopic molecular arrangement of a nematic liquid crystal (NLC) material namely 4 cyano-4ʹ-pentylbiphenyl (5CB). To achieve the objective, we have adopted various concentrations (0.25, 0.5 and 1 wt%) of ITO NPs in 5CB and filled them in the homogeneously aligned sample cells to observe their influence on the dielectric and optical texture of the NLC under investigation. Firstly, polarizing optical micrographs under crossed polarizers were recorded to observe the uniform dispersion and miscibility of ITO NPs in the nematic phase of 5CB. These micrographs also infer the molecular rearrangement of 5CB material that is occurred under the simultaneous and cumulative anchoring effect induced by ITO NPs and aligning layers. Furthermore, the dielectric parameters (permittivity, loss and dielectric loss factor) of pristine and composites as the function of frequency, temperature and DC biasing have been studied. Surprisingly, dielectric permittivity and relaxation frequency of 0.25 wt% ITO NPs composite was found to be the maximum that is decreased with further increment in the concentration of ITO NPs. We have also confirmed the thermal stability of 0.25 wt% ITO NP-induced changes in 5CB. Apart from it, by virtue of temperature-dependent dielectric anisotropy and optical textures, we have reported a significant decrement (∼14 %) in clearing temperature of 5CB. These results will pave the way to devise a system with ITO NPs as the dopant in order to obtain desired phase transition temperature of liquid crystal materials.

Eliminating Ambiguities in Electrical Measurements of Advanced Liquid Crystal Materials

Existing and future display and non-display applications of thermotropic liquid crystals rely on the development of new mesogenic materials. Electrical measurements of such materials determine their suitability for a specific application. In the case of molecular liquid crystals, their direct current (DC) electrical conductivity is caused by inorganic and/or organic ions typically present in small quantities even in highly purified materials. Important information about ions in liquid crystals can be obtained by measuring their DC electrical conductivity. Available experimental reports indicate that evaluation of the DC electrical conductivity of liquid crystals is a very non-trivial task as there are many ambiguities. In this paper, we discuss how to eliminate ambiguities in electrical measurements of liquid crystals by considering interactions between ions and substrates of a liquid crystal cell. In addition, we analyze factors affecting a proper evaluation of DC electrical conductivity of advanced multifunctional materials composed of liquid crystals and nanoparticles.

Liquid Crystal Materials for Biomedical Applications.

Liquid crystal is a state of matter being intermediate between solid and liquid. Liquid crystal materials exhibit both orientational order and fluidity. While liquid crystals have long been highly recognized in the display industry, in recent decades, liquid crystals provide new opportunities into the cross-field of material science and biomedicine due to their biocompatibility, multifunctionality, and responsiveness. In this review, the latest achievements of liquid crystal materials applied in biomedical fields are summarized. The start is made by introducing the basic concepts of liquid crystals, and then shifting to the components of liquid crystals as well as functional materials derived therefrom. After that, the ongoing and foreseeable applications of liquid crystal materials in the biomedical field with emphasis put on several cutting-edge aspects, including drug delivery, bioimaging, tissue engineering, implantable devices, biosensing, and wearable devices are discussed. It is hoped that this review will stimulate ingenious ideas for the future generation of liquid crystal-based drug development, artificial implants, disease diagnosis, health status monitoring, and beyond.

A Review on Physical, Chemical and Optical Properties of Liquid Crystal

The foundation of the upcoming generation of cutting-edge gadgets and digitally augmented technologies is expected to be smart soft materials. Because of their responsiveness and adaptability, liquid crystals (LCs) are promising smart soft materials. In the 20th century, LCs were crucial to changing the information display sector. However, several beyond-display uses for LCs have been proven at the turn of the twentieth century, neatly using their controlled stimuli-responsive and adaptable properties. New LC materials have been developed and engineered for such applications. The review comes close with a summary and viewpoints on the potential and problems facing LCs as smart soft materials. This review is expected to inspire a wide range of concepts for the application of nature's delicate phase of matter in the generation and beyond of smart and augmented devices.

Beam scanning leaky wave antenna based on liquid crystals with gesture-controlled system

ABSTRACT Controlling objects with body language is an extremely interesting ability for human beings. Recognizing different gestures is an effective way to collect valuable information, which is used to switch the radiation characteristic of beam scanning antennas. However, most existing beam scanning antennas are wire-connected and manually controlled by users. Thereby, a novel framework of gesture-controlled antennas is proposed in this paper. Rather than DC voltages supplied by powers or AC voltages supplied by signal generators, the beam scanning antenna can be effectively controlled by different gesture commands collected in real time from the user. On this basis, considering the advantages of the low cost and wide frequency band of liquid crystal (LC) materials, a LC-based fixed-frequency beam scanning leaky wave antenna (LWA) with gesture-controlled systems is demonstrated as one example. Different gestures can be recognised as controlled information to supply corresponding output signals by field programmable gate arrays (FPGAs) for the LC-based LWA. Based on the proposed framework, a verification system is tested, which demonstrates that the radiation characteristic can be effectively controlled by the user’s gesture. This work supplies a novel way for intelligent beam scanning antennas with potential applications in the internet of things (IoT), satellite and 5 G/6 G communications.

Chemically and biochemically responsive liquid crystal polymer networks and elastomers

AbstractChemically responsive liquid crystal (LC) based polymers can change their mechanical or optical properties when exposed to chemical triggers. The anisotropy inherent in LC materials allows the programming and control of predictable changes in shape, stiffness, and/or color. By further incorporating ionizable moieties into the polymer formulation, these materials may exhibit a response to chemical stimuli such as pH, solvents, or specific analytes. This mini‐review highlights seminal papers and recent advances in the use of chemoresponsive LC polymers for sensing and actuation. We also discuss how these materials can respond to biochemical stimuli through the immobilization of enzymes into the network, and provide examples of different types of responses (e.g., shape reconfigurations and color transitions). Multiple ways of modulating the response, such as chemical gating and enzyme patterning, are also reviewed. Finally, we illuminate some of the challenges and opportunities in the use of these materials for state‐of‐the‐art applications, including shape‐controllable medical implants and real‐time field‐deployable sensors. © 2023 Society of Industrial Chemistry.

Solid-Liquid Crystal Biphasic Ferroelectrics with Tunable Biferroelectricity.

Ferroelectricity has been separately found in numerous solid and liquid crystal materials since its first discovery in 1920. However, a single material with biferroelectricity existing in both solid and liquid crystal phases is very rare, and the regulation of biferroelectricity has never been studied. Here, solid-liquid crystal biphasic ferroelectrics, cholestanyl 4-X-benzoate (4X-CB, X = Cl, Br, and I), which exhibits biferroelectricity in both the solid and liquid crystal phases, is presented. It is noted that the ferroelectric liquid crystal phase of 4X-CB is a cholesteric one, distinct from the ordinary chiral smectic ferroelectric liquid crystal phase. Moreover, 4X-CB shows solid-solid and solid-liquid crystal phase transitions, of which the transition temperatures gradually increase from Cl to Br to I substitution. The spontaneous polarization (Ps ) of 4X-CB in both solid and liquid crystal phases can also be regulated by different halogen substitutions, where the 4Br-CB has the optimal Ps because of the larger molecular dipole moment. To the authors' knowledge, 4X-CB is the first ferroelectric with tunable biferroelectricity, which offers a feasible case for the performance optimization of solid-liquid crystal biphasic ferroelectrics.

Metallomesogens as potential materials for improvement of electro-optical properties of commercial liquid crystals

We present a new approach to utilize the eutectic metallomesogen (MOM) mixtures to improve the electro-optical properties of commercial nematic liquid crystal (NLC) materials. Accordingly, we studied the phase diagrams of rod-like MOM models structures, including alkyl/alkoxy-azobenzene with Pd complex and salicylal-diaminates with Cu, Ni and Pd complexes. These phase diagrams we utilized the eutectic MOM mixtures and mixed them with few commercial NLC hosts. The results showed a complete mesogenic miscibility and wide mesogenic range. Although the studied MOM model materials are not the optimum structures and we did not study the electro-optical properties of MOM-NLC mixtures, the present results indicate the potential application of MOMs to improve the performance of commercial NLC, which require further future studies.

Photoaligned Liquid Crystalline Structures for Photonic Applications

With the advancement of information display technologies, research on liquid crystals is undergoing a tremendous shift to photonic devices. For example, devices and configurations based on liquid crystal materials are being developed for various applications, such as spectroscopy, imaging, and fiber optics. One of the problems behind the development of photonic devices lies in the preparation of patterned surfaces that can provide high resolution. Among all liquid crystal alignment techniques, photoalignment represents a promising non-contact method for the fabrication of patterned surfaces. In this review, we discuss the original research findings on electro-optic effects, which were mainly achieved at the Department of Electronic and Computer Engineering of the Hong Kong University of Science and Technology and the collaborating research laboratories.

SYNTHESIS, PROPERTIES, AND APPLICATIONS OF SUPRAMOLECULAR LIQUID CRYSTAL MATERIALS AND ACRYLAMIDE PORPHYRIN POLYMERS

A review of the work in the field of design, study of properties, and application of liquid crystal materials and acrylamide porphyrin polymers, performed at the Department of Chemistry and Technology of High-molecular Compounds, in the laboratory of Supramolecular and liquid crystal systems and in the laboratory of Polymer materials of the Research Institute of Macroheterocyclic compounds of the Ivanovo State University of Chemical Technology over the past 10 years, is presented. Synthetic methods were developed, mesogenic compounds and mixed liquid crystal compositions based on classical and supramolecular mesogens doped with additives containing polar, amphiprotic and chiral groups were obtained and studied. The mechanisms of chiral transport in the mesophase were studied. The results on the use of liquid crystals as light and heat stabilizers of polymeric materials are presented. Stationary phases for gas-liquid chromatography based on supramolecular mesogens, macroheterocyclic compounds with high structural selectivity with respect to various isomers were developed. Methods have been developed for the synthesis of water-soluble porphyrin polymers and porphyrin-containing hydrogels based on acrylamide and synthetic porphyrin monomers, realizable both under thermal heating and under microwave radiation. It is shown that a change in the ratio and nature of the components, as well as the polymerization conditions in the synthesis of porphyrin polymers provides targeted control of the properties of the resulting compounds. The molecular-mass and spectral characteristics of the obtained polymers, their surface morphology and sorption properties of porphyrin-containing acrylamide hydrogels are investigated. For citation: Burmistrov V.A., Aleksandriiskii V.V., Novikov I.V., Pechnikova N.L., Shilov I.V., Lyubimtsev A.V., Ageeva T.A., Koifman O.I. Synthesis, properties, and applications of supramolecular liquid crystal materials and acrylamide porphyrin polymers. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 31-51. DOI: 10.6060/ivkkt.20236607. 6832j.

Optimizing liquid crystal cell thickness in electro-optical Fresnel lenses through theoretical calculations and experimental validation.

Tunable liquid crystal (LC) lenses have gained significant attention in recent decades due to their lightweight, low cost, and versatility in applications such as augmented reality, ophthalmic devices, and astronomy. Although various structures have been proposed to improve the performance of LC lenses, the thickness of the LC cell is a critical design parameter that is often reported without sufficient justification. While increasing the cell thickness can lead to a shorter focal length, it also results in higher material response times and light scattering. To address this issue, the Fresnel structure has been introduced as a solution to achieve a higher focal length dynamic range without increasing the cell thickness. In this study, we numerically investigate, for the first time (to our knowledge) the relationship between the number of phase resets and the minimum required cell thickness to achieve a Fresnel phase profile. Our findings reveal that the diffraction efficiency (DE) of a Fresnel lens also depends on the cell thickness. Specifically, to achieve a fast response Fresnel-structured-based LC lens with high optical transmission and over 90% DE using E7 as the LC material, the cell thickness should fall within the range of 13 to 23 µm.

Synthesis of Thiophene-Based Derivatives and the Effects of Their Molecular Structure on the Mesomorphic Behavior and Temperature Range of Liquid-Crystalline Blue Phases

The development of blue-phase liquid crystal (BPLC) materials with a wide temperature range is of great significance for practical applications in the optoelectronic field. In the study, bent-core derivatives with a 3-hexyl-2,5-disubstituted thiophene central ring in the λ-shaped molecular structure were designed and synthesized. Their mesomorphic behavior and effect on the blue-phase (BP) temperature range were investigated. Interestingly, a BP was achieved both during the heating and cooling processes by doping with a proper concentration of chiral compound into the thiophene bent-shaped molecule with high rigidity, while derivatives with fluorine atom substitution only exhibited cholesteric phase no matter how many chiral compounds were added. This result proved that BP is highly sensitive to the molecular structures of bent-shaped molecules. Moreover, the BP temperature range was broadened when adding these molecules into a BPLC host, which thus improved the BP temperature range from the initial value, no more than 4 °C, to as much as 24 °C. The experimental phenomena were reasonably explained through molecular simulation calculations. The study may provide some experimental basis and theoretical guidance for the design of novel bent-shaped molecules and BPLC material with a wide temperature range.

P‐87: New Liquid Crystal Materials for Outdoor Displays

Outdoor displays are widely applied in markets, rail transits and bus stations as a replacement for traditional posters. Due to the relatively harsh operation environment, materials for outdoor displays, such as liquid crystals (LCs), require better stability and reliability than normal indoor products. Herein, to evaluate the difference in reliability and optical properties between normal LCs and outdoor LCs, three LC materials including one normal LC, named LC‐Ref, and two outdoor LCs, LC‐1 and LC‐ 2, were assessed. Compared with LC‐Ref, LC‐1 and LC‐2 displayed wider nematic phase ranges and better reliability. Even though outdoor LCs exhibited right‐shifted V‐T curves, LC‐1 and LC‐2 could achieve similar transmittance ratios with LC‐Ref utilizing high driving voltage. Moreover, utilizing high‐ brightness backlight units (BLUs), outdoor LCs showed faster Toff than LC‐Ref with normal BLUs. Overall, LC‐1 and LC‐2 are potentially excellent LC materials for outdoor displays.

Phase degradation of liquid crystal variable retarders and preconfiguring method for high-power continuous-wave laser

The effects of laser-induced heat on the performance degradation of liquid crystal (LC) devices are critically important in applications involving laser systems. In this study, we investigated the influences of 1064-nm continuous-wave (CW) laser loading on an LC variable retarder (LCVR). The results show that thermal deposition initially causes an overall downward shift in the electronically controlled phase retardation curve. This phase retardation reduction is restored under a certain voltage and laser power by reducing the driving voltage. For common nematic LC wave plates that do not require voltage application, the decrease in phase retardation can be pre-compensated by increasing the corresponding LC cell thickness. For electrically controlled LC devices, the phase retardation under a high-power CW laser can be preconfigured by plotting phase response curves versus voltages at different laser powers. Based on these calibration curves, the LC devices can still service high-power CW lasers as long as the resulting temperature does not reach the clear point of the LC material. These results clarify the fundamental mechanisms of phase modulation variation induced by thermal deposition and could be useful for the fabrication optimization and effective implementation of LC devices in high-power laser systems.

Studies of temperature dependent Raman spectroscopy of two nematic liquid crystalline compounds of homologous series

Raman spectroscopy is an important tool to understand the structural and molecular behaviour of the liquid crystals when they undergo through different temperatures. It also helps to understand the different phase changes of the liquid crystal material as temperature changes. In this work, the structural properties of two nematic liquid crystals having relatively high clearing temperature namely 4 butylcyclohexyl-3, 5-difluoro-4- isothiocyanato biphenyl and 4-pentylcyclohexyl-3, 5-difluoro-4-isothiocyanato biphenyl are studied. The study is done using temperature dependent Raman spectroscopy. From the studies of the two compounds it has been found that the experimental values are agree well with the various functional groups and different bond assignments recorded in literature. This agreement validates the presence of different functional groups and different stretching bonds in the two studied liquid crystal compounds. Deformations of some of the peak positions of the two liquid crystal compounds have been observed with the change in phase at different temperature. Also to understand the behaviour of the Raman peak near the clearing temperatures of the liquid crystal compounds the linewidth of the different peak values at different temperature have also been studied. From the line width study, the various phase transition temperatures of the two liquid crystalline compounds can be confirmed.

Improve Perovskite Solar Cell Stability and Efficiency via Multifunctional Multiple‐Ring Aromatic Dopant Passivation

Organic–inorganic perovskite solar cells, as a representative of the new generation of solar cells, have made satisfactory advancements in development over the past few years. However, the low carrier transport characteristics and energy loss brought on by defects severely restrict its development. This study develops a new liquid crystal material 1‐naphthalene acetic acid potassium salt (C12H9KO2, K‐NAA) as a dopant into the MA0.6FA0.4PbI3−xClx material. The presence of free K+ ions in K‐NAA modifies the perovskite lattice gap, and the CO structure can efficiently passivate the Pb2+ defect caused by the absence of coordination. Therefore, the grain boundaries, which serve as points of moisture penetration become blurred, hence suppressing charge trapping/recombination centers and enhancing the film quality and stability. The naphthalene in K‐NAA has a conjugated multiple‐ring aromatic structure. The abundant π‐electron delocalization present in the conjugated structure of the benzene ring may provide an electron‐rich environment outside the connected crystal structure, resulting in field‐effect passivation and effectively enhancing carrier transport performance. Hence, the devices deliver a champion power conversion efficiency (PCE) of 19.86%. After 700 h under the dark at 25 °C and 30% humidity, the optimized unencapsulated device PCE maintains at 92% of its initial efficiency.

Diverse Synthetic Transformations Using 4-Bromo-3,3,4,4-tetrafluorobut-1-ene and Its Applications in the Preparation of CF2 CF2 -Containing Sugars, Liquid Crystals, and Light-Emitting Materials.

Organic molecules with fluoroalkylene scaffolds, especially a tetrafluoroethylene (CF2 CF2 ) moiety, in their molecular structures exhibit unique biological activities, or can be applied to functional materials such as liquid crystals and light-emitting materials. Although several methods for the syntheses of CF2 CF2 -containing organic molecules have been reported to date, they have been limited to methods using explosives and fluorinating agents. Therefore, there is an urgent need to develop simple and efficient approaches to synthesize CF2 CF2 -containing organic molecules from readily available fluorinated substrates using carbon-carbon bond formation reactions. This personal account summarizes the simple and efficient transformation of functional groups at both ends of 4-bromo-3,3,4,4-tetrafluorobut-1-ene and discusses its synthetic applications to biologically active fluorinated sugars and functional materials, such as liquid crystals and light-emitting molecules.

A Highly Sensitive Sensing Technique via Surface Plasmons With Tunable Prism Refractive Index

A new perspective using Kretschmann configuration is presented to excite surface plasmon polaritons (SPP) at liquid crystal (LC)/metal interface. The excitation of SPP takes place through the electrical tuning of the prism refractive index instead of the commonly used angular interrogation. The results show that the proposed methodology is 30% superior to the traditional angular interrogation. The 5CB (4-pentyl-4’-cyanobiphenyl) is one of the best suited nematic LC material for the proposed detection framework. Its refractive index is linearly tunable in the range 1.55 ~ 1.78 (at wavelength 1.55 μm) via an external applied electric field. In that range of refractive index variation, the SPP modes are efficiently excited; and hence any minute variation in the analyte refractive index can be detected reliably and accurately through a simple tuning of the refractive index of the prism LC material. The fundamental characteristics of the sensor are assessed through the evaluation of the linearity, sensitivity (S), the full width at half maximum (FWHM) of the reflectivity curve and the figure of merit (FOM). The variation of these characteristics over a whole range of analyte refractive index (1.3–1.4) are presented as well. The electrical tuning provides a well-matched design with micro-scale devices.