Search Results (31)

A thermochromic cholesteric liquid crystal (CLC) mixture was prepared using epoxies. The structural color of the CLCN film was tuned by changing the concentration of a chiral dopant and the polymerization temperature. It was found the yellow CLCN film can be used as a sensor for the discrimination of methanol and ethanol which was proposed to be driven by the difference between the solubility parameters. Moreover, a colorful pattern was prepared based on the thermochromic property of the CLC mixture, which could be applied for decoration and as a sensor for chloroform. Full article

This study developed cholesteric liquid crystal broadband reflective films using zinc oxide nanoparticles (ZnO NPs) and homotriazine UV-absorbing dye (UV-1577) to enhance infrared shielding. Unlike benzotriazole-based UV absorber UV-327, which suffers from volatility and contamination, UV-1577 exhibits superior compatibility with liquid crystals, higher UV absorption efficiency, and enhanced processing stability due to its larger molecular structure. By synergizing UV-1577 with ZnO NPs, we achieved a gradient UV intensity distribution across the film thickness, inducing a pitch gradient that broadened the reflection bandwidth to 915 nm and surpassing the performance of previous systems using UV-327/ZnO NPs (<900 nm). We conducted a detailed examination of the factors influencing the reflective bandwidth. These included the UV-1577/ZnO NP ratio, the concentrations of the polymerizable monomer (RM257) and chiral dopant (R5011), along with polymerization temperature, UV irradiation intensity, and irradiation time. The resultant films demonstrated efficient ultraviolet shielding via the UV-1577/ZnO NPs collaboration and infrared shielding through the induced pitch gradient. This work presents a scalable strategy for energy-saving smart windows. Full article

The micro-phase segregation of two incompatible components on a nanometer scale results in a unique solvent-induced extended anisotropic arrangement. With the addition of a chiral dopant, lyotropic liquid crystals can be induced to adopt a helical structure, forming lyotropic cholesteric liquid crystals capable of reflecting incident light. In this study, to prevent fluid leakage in lyotropic materials, we encapsulated a series of hydrogel-stabilized lyotropic liquid crystals, presenting tunable structural colors visible in all directions, mimicking the color-changing characteristics of living organisms. Hydrogel scaffolds with controllable swelling behaviors were engineered by incorporating crosslinking monomers. To ensure stable integration of lyotropic liquid crystals, high-boiling-point ethylene glycol was employed as a fluid during the fabrication process. This study extensively explores the relationship between tensile force, temperature, and pressure and the color changes in lyotropic liquid crystals (LC). The results indicate that lyotropic LC membranes, stabilized by ethylene glycol and PDMS encapsulation, exhibit long-term stability, rendering them suitable for applications in temperature and pressure sensing. This approach ensures the continuous presence and stability of lyotropic liquid crystals within the hydrogel matrix. Full article

The realization of broad-wavelength tunability of the structural color in Double layered Cholesteric Liquid Crystal Elastomers (DCLCEs), along with good flexibility and processability, presents a significant challenge. This research introduces a facile and effective fabrication technique, Solvent Evaporation-Induced Self-Assembly (SEISA), for the production of DCLCEs exhibiting broad wavelength tunability, superior flexibility, and robust mechanical characteristics. Focusing on initial color tuning, bubble defect minimization, UV photopolymerization, and coating procedures, this research systematically optimizes the fabrication process through experimental investigation of factors like chiral dopant amount, temperature, UV exposure duration, coating thickness, and speed. The method enabled the successful fabrication of DCLCEs with uniform and controllable coloration, demonstrating the effectiveness of this controlled synthesis approach in significantly enhancing structural color features. Upon stretching to 2.8 times its original length, the center wavelength shifted from 613 nm to 404 nm, yielding a tunable bandwidth of up to 209 nm across the visible spectrum. Full article

This study focuses on the ionic contribution by a chiral dopant added into a nematic host for preparing cholesteric liquid crystals (CLCs). Chiral structures were designated by individually incorporating two enantiomers, R5011 and S5011, into the nematic E44 to construct right- and left-handed CLCs, respectively. Characterized by the space-charge polarization, the dielectric spectra of the CLCs were investigated in the low-frequency regime, where f  ≤  1 kHz. The role of the individual chiral dopant, R5011 or S5011, at concentrations of 0–4.0 wt.% in altering the ionic properties of the CLC material was analyzed by deducing the electrical conductivity, ion density, and ion diffusivity. Regardless of the cell structure to be antiparallel or twisted by 90°, a significant ionic response was observed in the right-handed CLCs in comparison with the left-handed counterparts, suggesting that excess ions originating from our R5011 were introduced into the mesogenic mixtures. This work alarms the potential contribution of notorious impurity ions by a chiral dopant, which is often ignored in fabricating CLCs for electro-optical applications. Full article

The results of an experimental investigation of the temperature and wavelength dependence of the Kerr constant (K) of mixtures with an increasing amount of chiral dopant in an isotropic liquid crystal phase are reported. The material was composed of a nematic liquid crystal (5CB) and a chiral dopant (CE2), which formed non-polymer-stabilized liquid crystalline blue phases with an exceptionally large value of K∼2 × 10⁻⁹ mV⁻². The measurements were performed on liquid and blue phases at several concentrations covering a range of temperatures and using three wavelengths: 532 nm, 589 nm and 633 nm. The work focused on changes caused by concentration and their impact on the increase in the value of K, and it was found that in the case of the 5CB/CE2 mixture these changes were significant and quite systematic with temperature and wavelength. It is shown that the dispersion relation based on the single-band birefringence model described K well in isotropic liquid crystal phases at all of the measured concentrations. In an isotropic fluid, both temperature-dependent parameters in the dispersion relation had a simple linear form and, therefore, the K-surface could be described by only four constants. In the blue phase, the expression reproducing the temperature variation of K depended on concentration, which could vary from being almost linear to quasi-linear and could be represented well by an inverse exponential analytic expression. Full article

The reverse-mode smart windows, which usually fabricated by polymer stabilized liquid crystal (PSLC), are more practical for scenarios where high transparency is a priority for most of the time. However, the polymer stabilized cholesteric liquid crystal (PSCLC) film exhibits poor spacing stability due to the mobility of CLC molecules during the bending deformation. In this work, a reverse-mode PSCLC flexible film with excellent bending resistance was fabricated by the construction of polymer spacer columns. The effect of the concentration of the polymerizable monomer C6M and chiral dopant R811 on the electro-optical properties and polymer microstructure of the film were studied. The sample B2 containing 3 wt% of C6M and 3 wt% R811 presented the best electro-optical performance. The electrical switch between transparent and opaque state of the flexible PSCLC film after bending not only indicated the excellent electro-optical switching performance, but also demonstrated the outstanding bending resistance of the sample with polymer spacer columns, which makes the PSCLC film containing polymer spacer columns have a great potential to be applied in the field of flexible devices. Full article

Nematic chiral liquid crystals (CLCs) are characterized by a helical arrangement of nematic LC molecules. A layer of CLC typically exhibits an optical reflection band due to Bragg reflection in the helical structure. When several layers of CLC are spin-coated and polymerized on top of each other without a barrier layer in between, defect modes can form in their reflection spectrum. By comparing experimental results and simulations, we investigate the origin of the defect modes, thereby revealing details on the behavior of the materials at the interfaces during deposition. Simulations show that these defect modes can originate from the migration of chiral dopant leading to a layer with a smaller pitch or from a discontinuity in the director orientation at the interface between two layers. Full article

We have designed new chiral smectic mesogens with the -CH₂O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics. Full article

Nematic liquid crystals (LCs) are known to undergo a phase transition to chiral nematic LCs possessing helices upon doping with enantiomeric molecules known as chiral dopants. The relationship between the helical pitch ($p$), the molar fraction ($x$), and the power of the chiral dopant to induce a helix in a nematic solvent (${\beta }_M$) is expressed as $p=1/\left(x·{\beta }_M\right).$ The helical pitch is easily controlled by the concentration of the chiral dopant when the dopant molecule is miscible with the host nematic LC. However, it has not yet been clarified what the miscibility of the chiral dopant molecules with the nematic LCs depends. Therefore, we performed all-atom molecular dynamics (MD) simulations for the system composed of both Δ and Λ isomers of a chiral dopant molecule dispersed in a nematic LC and investigated the relationship between the microdynamics of the chiral molecules and their miscibility with the nematic solvent. The miscibility of the chiral dopant molecules with the LC solvent was found to correlate with the diffusion coefficient of the LC solvent. In the system where the chiral dopant molecules with high miscibility were added, the diffusion coefficient of the LC solvents was comparable to that of the system in which the chiral molecule was not doped. Furthermore, it was confirmed that more elongated chiral dopants were more miscible with the nematic solvent consisting of calamitic molecules, and that these dopant molecules did not have a significant effect on the diffusion behavior of the LC molecules. Full article

Nature is highly efficient at producing chiral compounds that are enantiomerically pure. The inherent chirality of naturally occurring biomolecules means that many have the potential to be used as chiral dopants for cholesteric liquid crystal (CLC) systems. Though many biomolecules have been identified as chiral dopants, many remain yet to be probed for their ability to function as chiral dopants. Here, 10 naturally occurring biomolecules comprised of steroids and bile acids were tested as chiral dopants for CLCs. Progesterone was identified as having high miscibility with nematic liquid crystals and was used in responsive liquid crystal devices. Progesterone-doped CLC devices were fabricated to exhibit either normal mode or reverse mode switchable behavior. Polymer stabilized CLCs (PSCLC) devices exhibiting dynamic electro-optic red- and blue-tuning behaviors were also fabricated. Furthermore, immiscible lithocholic acid was synthetically modified to afford two derivatives that were miscible at 10 wt. % in nematic liquid crystals. The two lithocholic acid derivatives were used as chiral dopants and incorporated into polymer stabilized CLCs which exhibited blue tuning behavior. Full article

Chromonic liquid crystals have recently received a lot of attention due to their spontaneous self-assembly in supramolecular columnar structures that, depending on their concentration in water, align to form a nematic liquid crystalline phase. The chirality may be induced in chromonics by adding chiral moieties to the nematic phase or enhanced by confining them in curved geometrical constraints. This review summarizes the recent research developments on chiral chromonic liquid crystals confined in spherical geometry, relating the results to what was observed for thermotropic liquid crystals in the same conditions. The review focuses on the studies carried out on commercially available nematic chromonics, investigating the effects on their topologies in different anchoring conditions and different chiral dopants and suggesting an application in the sensor field. Full article

The experimental and theoretical study of influence of the conformational state and association on the chirality of the stereochemically nonrigid biologically active bis-camphorolidenpropylenediamine (CPDA) and its ability to induce the helical mesophase of alkoxycyanobiphenyls liquid–crystalline binary mixture was carried out. On the basis of quantum-chemical simulation of the CPDA structure, four relatively stable conformers were detected. A comparison of the calculated and experimental electronic circular dichroism (ECD) and ¹H, ¹³C, ¹⁵N NMR spectra, as well as specific optical rotation and dipole moments, allowed to establish the most probable trans-gauche conformational state (tg) of dicamphorodiimine and CPDA dimer with a predominantly mutually parallel arrangement of molecular dipoles. The induction of helical phases in LC mixtures based on cyanobiphenyls and bis-camphorolidenpropylenediamine was studied by polarization microscopy. The clearance temperatures and the helix pitch of the mesophases were measured. The helical twisting power (HTP) was calculated. The decrease in HTP with increasing dopant concentration was shown to be connected with the CPDA association process in the LC phase. The effect of camphor-containing chiral dopants of various structures on nematic LCs was compared. The values of the permittivity and birefringence components of the CPDA solutions in CB-2 were measured experimentally. A strong effect of this dopant on the anisotropic physical properties of the induced chiral nematic was established. A significant decrease in the dielectric anisotropy was associated with the 3D compensation of the LC dipoles during the formation of the helix. Full article

Cholesteric liquid crystals (CLC) were widely used in optical devices as one-dimensional photonic crystals. However, their reflective bands cannot be adjusted, which limits their wide application in many fields. In this paper, a series of ionic chiral ferrocene derivatives (CD-Fc⁺) as dopants were designed and prepared, and their doping into negative liquid crystal matrix was investigated to develop cholesteric response liquid crystal composites with electrically tunable reflective bands. The effects of electric field frequency, voltage, retention time of voltage and molecular structure on the broadening of reflection bandwidth were investigated in detail. Full article

Cholesteric liquid crystals (CLCs) are a significant class of temperature-responsive photonic materials that have the ability to selectively reflect light of a specific wavelength. However, the fabrication of main-chain CLC oligomers with dramatic reflection band variation upon varying the temperatures remains a challenge. Here, a feasible method for improving and controlling the responsiveness of main-chain cholesteric liquid crystal oligomers by the incorporation of a smectic monomer is reported. The smectic monomer strengthens the smectic character of the oligomers and enhances the magnitude of the change of the pitch as a function of temperature upon approaching the cholesteric–smectic phase transition temperature. The central wavelength of the reflection band can be easily modified by mixing in an additional chiral dopant. This promising method will open the door to the preparation of temperature-responsive photonic devices with excellent responsiveness. Full article