Liquid Crystal Systems Research Articles

Micro/nanogroove-structured graphene-oxide-doped indium gallium yttrium oxide alignment layer with improved electrical characteristics

Graphene oxide (GO)-doped indium gallium yttrium oxide (InGaYO) alignment layers formed by a brush-based solution-coating process are reported in this study. The doping concentrations were adjusted to 0, 5, and 15 wt%. The alignment layers obtained thus showed anisotropic micro/nanogroove structures having induced by shear stress originating from the brush-hair movements. This structure enabled uniform and homogeneous liquid crystal (LC) alignment on the film surface with geometric constraints. The alignment state was verified by polarized optical microscopy and pretilt angle analysis. The GO-doped InGaYO alignment layer demonstrated enhanced 1.92 × 10−4 Jm−2 polar anchoring energy of the LCs and reduced hysteresis property, which aid in lower image-sticking effects. The LC device operation was verified with 1.7 V in a twisted-nematic LC system along with stable optical transmittance control. From these results, GO doping of the metal-oxide alignment layer shows the potential for functional LC device applications.

Low-voltage electrochromic behaviour of polymer-stabilised liquid crystal with considerable broadband reflection

ABSTRACT In this work, a novel method was proposed to achieve electric-induced colouration of polymer-stabilised liquid crystal (PSLC) with considerable broadband reflection. The formation of broadband reflection was due to the introduction of the UV absorber that induced a light intensity gradient within the liquid crystal system and promoted the non-uniform distribution of the pitch. Experiments were performed to optimise the components and polymerisation conditions, allowing the bandwidth to be broadened from 252 nm to 906 nm. The texture of PSLC was characterised using POM, revealing that the planar texture was not disrupted. Thereafter, the addition of ionic liquid as supporting electrolyte enabled the PSLC to be switched from colourless to coloured at DC voltage as low as 1.7 V and the colouration behaviour can be independently modulated by changing the voltage level and the duration. Meaningfully, after the DC electric field was removed, the colour of the PSLC can also disappear gradually. In addition, the as-prepared electrochromic PSLC presented enhanced UV shielding, IR thermal control efficacy and good colouration performance on flexible substrates, which can be applied to low-energy smart glass and thermal management of buildings. This study provided a promising approach for the development of smart optical devices.

High-Δn tolane-liquid crystal diluters with low melting point and low rotational viscosity

High birefringence (Δn) and low melting point (Tm), high Δn and low rotational viscosity (γ1) are two pairs of contradictory performance parameters. In this work, two high-Δn LC diluters 3PTPF2V and 3PTPFOV are proposed to achieve a fine balance between them. These target compounds containing a rigid tolane core, a lateral fluorine substituent and a buty-3-enyl or allyloxy terminal group were further synthesized. Some experimental instruments, such as POM, DSC, Abbe refractometer, multi-channel liquid crystal evaluation system, were adopted to investigate their properties of mesomorphic phase behavior, Tm, Δn and γ1 by comparing with classical LC diluters 3HHV and V2PTP2V. Meanwhile, density functional theory (DFT) calculations were employed to correlate the experimental results, and their comprehensive effects on two high-Δn LC mixtures were further evaluated. Research results indicated that both target compounds possess low Tm (∼20 °C), low γ1 (∼6.5 mPa·s), and high Δn (>0.26). Performance in high-Δn LC mixture demonstrated that they could effectively decrease Tm and γ1, meanwhile maintain high Δn and Tc values, meaning their potential application prospects in fast-response LC optical devices.

Enhanced dielectric, electrical and electro-optical properties: Towards understanding the interaction in mesophases of 8OCB liquid crystal dispersed with CdSe/ZnS quantum dots

The current advancements in developing new liquid crystalline materials for the next generation applications focus mainly on improving the physical characteristics of the liquid crystal (LC) systems. Recent progress has shown that the functionalized nanoparticles embedded in LC matrices can significantly alter the characteristics of the LC material based on the mutual interaction between the host molecules and guest particles. In this aspect, the present study reports the impact of dispersing core-shell type CdSe/ZnS quantum dots (QDs) on the dielectric, electrical and electro-optical properties of the 8OCB LC doped at various concentrations. The doped samples exhibit an ion releasing behavior and this effect becomes more evident as the doping concentration increases up to 0.2 wt% in the LC system. It is explained as a result of the growing tactoid-like ellipsoidal form acquired by QDs owing to the enhanced mutual interaction among QD ligands and rod-like LC molecules. The temperature variation of the diffusion constant, conductivity, ionic mobility and mean relaxation time of ions significantly follows each other in all the studied samples. Moreover, thermal profiles of the dielectric anisotropy, threshold voltage and splay elastic constant show a decreasing pattern with an increment in doping concentration. A dual-relaxation regime is experimentally investigated, corresponding to the contribution of nematic director and dimers, providing two kinds of rotational viscosity in the pristine and QDs dispersed LC samples. The transmittance-voltage curve reveals the presence of residual value in the dispersed samples and is related to the volatile memory effect. A slight enhancement is observed in the photoluminescence intensity for the lower doped sample and reduces further with increasing doping concentration in the pristine LC system. All these findings suggest the considerable contribution of functionalized QDs to the studied properties in terms of interaction between the LC and dopant material. This study will further elucidate the selection of optimal QDs concentration based on the required properties for their potential applications in futuristic devices based on LCs.

Lamellar liquid crystals formed from sucrose ester and Brij97 solutions for curcumin delivery

Abstract In this paper, the lamellar liquid crystals formed in S1570-Brij97/isopropyl myristate/PEG400 aqueous system were prepared at 37 °C. The effects of PEG400 and curcumin on the S1570-Brij97 lyotropic liquid crystal systems were studied by phase diagram, polarized optical microscopy, small angle X-ray scattering, and rheology. The prepared lamellar liquid crystals show stable structures at 37 °C. The encapsulation of curcumin improves the structural stability of the lamellar liquid crystals, which can be confirmed by their higher η γ=0.013 and σ y values, suggesting that the S1570-Brij97 lamellar liquid crystals are good carriers for curcumin. In addition, the prepared lamellar liquid crystals can effectively protect curcumin from decomposition, and curcumin can be released slowly in the liquid crystals. Therefore, based on the structural stability, protective effect on curcumin, and slow-release behavior, the constructed S1570-Brij97 lamellar liquid crystals have good potential for drug delivery.

AI on the Road: NVIDIA Jetson Nano-Powered Computer Vision-Based System for Real-Time Pedestrian and Priority Sign Detection

Advances in information and signal processing, driven by artificial intelligence techniques and recent breakthroughs in deep learning, have significantly impacted autonomous driving by enhancing safety and reducing the dependence on human intervention. Generally, prevailing ADASs (advanced driver assistance systems) incorporate costly components, making them financially unattainable for a substantial portion of the population. This paper proposes a solution: an embedded system designed for real-time pedestrian and priority sign detection, offering affordability and universal applicability across various vehicles. The suggested system, which comprises two cameras, an NVIDIA Jetson Nano B01 low-power edge device and an LCD (liquid crystal system) display, ensures seamless integration into a vehicle without occupying substantial space and provides a cost-effective alternative. The primary focus of this research is addressing accidents caused by the failure to yield priority to other drivers or pedestrians. Our study stands out from existing research by concurrently addressing traffic sign recognition and pedestrian detection, concentrating on identifying five crucial objects: pedestrians, pedestrian crossings (signs and road paintings separately), stop signs, and give way signs. Object detection was executed using a lightweight, custom-trained CNN (convolutional neural network) known as SSD (Single Shot Detector)-MobileNet, implemented on the Jetson Nano. To tailor the model for this specific application, the pre-trained neural network underwent training on our custom dataset consisting of images captured on the road under diverse lighting and traffic conditions. The outcomes of the proposed system offer promising results, positioning it as a viable candidate for real-time implementation; its contributions are noteworthy in advancing the safety and accessibility of autonomous driving technologies.

Recent Advances in Smart Windows Based on Photo-Responsive Liquid Crystals Featuring Phase Transition.

A smart window is an optical dimming device with intelligent functions that can control its relevant performances through external stimuli, achieving functions such as privacy protection and temperature regulation. Light is an ideal stimulus for regulating smart windows, which is noninvasive and allows self-adaptable manipulation of materials. This review highlights recent significant achievements in smart windows constructed by photo-responsive liquid crystals (LCs) systems that can undergo the transition between different phases. The smart windows based on photo-responsive LCs are used in a plethora of areas, including privacy protection, absorption glass, building decoration, energy saving, and climate modulation applications. The review concludes with a brief perspective on some significant challenges and opportunities for the future development of photo-responsive smart windows, which is crucial for expanding the applications of smart windows and improving their performances.

Improvement of rewriting time of optically driven liquid crystal display by azo-dye doping

ABSTRACT Optically driving liquid crystal display (ODLCD) uses polarized light field to control the orientation of the liquid crystal, and the display content can be maintained without external electric field, with extremely low power consumption. However, it has a long rewriting time, which is difficult to achieve industrialization. In order to improve the rewriting performance, the influence of the rotational viscosity of the mixed system of azo-dyes (SD1, MR) and nematic liquid crystal (5CB) on the rewriting speed is investigated. The experimental results show that the electro-optical properties of SD1-5CB and MR-5CB have great changes after irradiation by polarized light, among which the SD1-5CB is the best to improve the performance. With the increase of SD1 concentration, the rotational viscosity of SD1-5CB decreases significantly due to the change of cis-trans isomerization of azo-dye, and the optimal doping concentration is 0.5 wt%. In this case, the rewriting time is shortened from 45 s to 11 s, which has the potential to broaden the application of ODLCD.

Electrical tuning of branched flow of light

Branched flows occur ubiquitously in various wave systems, when the propagating waves encounter weak correlated scattering potentials. Here we report the experimental realization of electrical tuning of the branched flow of light using a nematic liquid crystal (NLC) system. We create the physical realization of the weakly correlated disordered potentials of light via the inhomogeneous orientations of the NLC. We demonstrate that the branched flow of light can be switched on and off as well as tuned continuously through the electro-optical properties of NLC film. We further show that the branched flow can be manipulated by the polarization of the incident light due to the optical anisotropy of the NLC film. The nature of the branched flow of light is revealed via the unconventional intensity statistics and the rapid fidelity decay along the light propagation. Our study unveils an excellent platform for the tuning of the branched flow of light which creates a testbed for fundamental physics and offers a new way for steering light.

Condensed state physics in biology: Liquid crystal - semiconductor system

The possibility of application of condensed state physics methods for the study of biological objects is considered. The object of use is a cell with a liquid crystal as a model of a biological system - a living cell. The system of liquid crystal - semiconductor was experimentally investigated by methods of modulation spectroscopy. By determining the value of electric reflection, it is possible to judge about the state of surface polarization of liquid crystal. Exposure to an electric field changes the energy of the semiconductor’s zone structure, which leads to changes in the optical properties of both crystals. To investigate the optical modulation changes in our case, we used the method with the use of electrolyte KOH, which allowed us to measure the modulation of the spatial charge. The study of thin layers (up to 120 μm) of various nematic liquid crystals has shown that at values of electric fields comparable to the Fredericks transition threshold, the orientation angle of liquid crystal molecules changes due to the interaction of surface polarization with the external field, and an odd electro-optic effect is observed. If the value of the electric field is much larger than the threshold of the Fredericks transition, the electric moment, which depends nonlinearly on the field, predominates and leads to an even electro-optic effect. The results of the study are proposed to be used for the development of new drugs and materials with specified parameters for medicine.

Existence and decay of global strong solutions to the nonhomogeneous incompressible liquid crystal system with vacuum and density-dependent viscosity

Existence and decay of global strong solutions to the nonhomogeneous incompressible liquid crystal system with vacuum and density-dependent viscosity

A chiral supramolecular liquid crystal based on pillararene and its application in information encryption.

A chiral supramolecular liquid crystal based on a pillararene mesogen was constructed. The regulation of liquid crystal behavior was achieved through the host-guest interactions between the pillararene-based mesogen and a tetraphenylethylene-containing guest. In addition, this supramolecular liquid crystal system, showing pH-responsive fluorescence emission character, was applied as an information encryption material capable of storing multiple levels of distinct information, thereby enriching the application of liquid crystal materials in the field of information security.

Electro‐Optic Topological Defect Devices Utilizing Nematic Liquid Crystal Binary Mixtures

Topological defects (TDs) manifest in many condensed matter systems. In liquid crystals (LCs), they occur as point or line singularities in the otherwise smooth director profile. Engineered and controllable TDs are of great interest for functional optoelectronic devices; however, the formation mechanism in patterned devices is not fully understood. In this work, electrically addressable TDs in doped mixtures of prototypical n‐alkyl‐cyanobiphenyl LCs 4‐cyano‐4′‐pentylbiphenyl (5CB) and 4‐cyano‐4′‐octylbiphenyl (8CB) are focused on. Doping concentrations of hexadecyltrimethylammonium bromide (CTAB) are varied and the effect of varying the host LC properties (through binary 5CB:8CB mixtures) on defect formation is studied. In the results, a strong correlation between LC “fluidity” and the ease of defect array formation is presented, with 0.5 wt% CTAB‐doped 5CB giving the best controllability/uniformity of TDs at low‐threshold voltages. Furthermore, it is demonstrated that the devices can be utilized as electrically switchable optical diffractive elements. In these findings, directions are mapped out that future studies can take in designing deterministic, electrically or magnetically tunable TD‐based photonic devices using LC systems.

Assessment of Approximations to the Embedding Potential in Frozen-Density Embedding Theory for the Calculation of Electric Field Gradients.

The approximations to the embedding potential in frozen-density embedding theory (FDET) have been assessed for the first time for the calculation of the electric field gradient (EFG) at a nucleus. FDET-based methods using a hierarchy of approximations are applied to evaluate the EFG at the nuclei of an HCl molecule in several noncovalently bound clusters chosen to represent potential liquid or molecular crystal systems. A detailed assessment of such approximations is made for the Hartree-Fock treatment of electron-electron correlation (both in FDET and in the reference calculations for the whole cluster). The emerging choice of the optimal set of approximations is reconfirmed in calculations in which electron-electron calculations are treated at the MP2 level. Our optimized protocol produces average errors in the complexation-induced EFG shift on the order of 25% relative to conventional quantum mechanical calculations for the whole cluster. This protocol is shown to be numerically robust and leads to enormous computational savings compared to a complete quantum mechanical treatment of the embedded species and its environment. For a cluster comprising a Na+ cation and up to 24 water molecules, the computation time is reduced by a factor of 30,000 at the expense of introducing an error in the environment-induced EFG shift of 22%.

Near-Infrared Reflective Polymer Films Based on UV-327-Doped Zinc Oxide Nanoparticles.

We prepared cholesteric liquid crystal (CLC) films with broadband reflective properties by admixing organic dye UV-327 into inorganic zinc oxide nanoparticles (ZnO NPs), utilizing the principle of pitch distribution from a large to a small gradient along the film thickness direction, leading to broadband reflection. ZnO NPs are poorly dispersed and easy to gather, but they do not decompose easily. The addition of UV-327 makes up for the above shortcomings. UV-327 is an organic compound with good compatibility and dispersion with liquid crystal systems. Therefore, we used the method of mixing two UV-absorbing dyes (UV-327 and ZnO NPs) to obtain CLC films. UV-absorbing dyes (UV-327 and ZnO NPs) made the liquid crystal films form a UV intensity gradient in the direction of thickness, prompting the polymerizable monomers to polymerize faster on the stronger side of the light, leading to the relative diffusion of chiral molecules and polymerizable monomers, forming the concentration gradient of chiral molecules in the direction of thickness. The pitch has a gradient distribution as the chiral concentration varies. Then, anchored by the polymer network, the pitch gradient distribution no longer changes. Broadened reflective bandwidth can reach up to 881 nm. Furthermore, the film covers the near-infrared wavelength band well, which can be applied to future smart windows or laser shielding for medical and military applications. It is also believed that this achievement will optimize the preparation technology of broadband reflective CLC films in the future.

Programmable Dynamic Information Storage Composite Film with Highly Sensitive Thermochromism and Gradually Adjustable Fluorescence.

The development of an integrated material system capable of effectively organizing and combining multisource information, such as dynamic pigmentary, structural, and fluorescent colors, is significant and challenging. Achieving such programmable dynamic information storage can considerably enhance the diversity and security of information deliveries. Here, a polymer-stabilized cholesteric liquid crystal system with highly temperature-sensitive structural color and light-sensitive pigmentary and fluorescence colors is presented. The prepared cholesteric liquid crystals (clcs) can reversibly change their structural color from red to blue within variational 3°C near room temperature, and exhibit a gradually adjustable fluorescence which can transform from blue to pink and finally to bright red. All this dynamic information is programmable and tailored, hundreds of thousands of (>540000) pattern combinations can easily be achieved by optical writing with a "bagua" pattern photomask. Therefore, if the corresponding code combinations to the pattern are assigned particular meanings, encrypted transmission of information with very high security can be achieved by utilizing applicable information encoding tables and decryption rules.

Antimicrobial peptide dendrimers assisted Nanocomposite-Loaded lyotropic liquid crystalline for multimodal surgical site infection management

Superficial incisional surgical site infections (SISSIs) were a serious challenge leading to delayed wound healing and even systemic diseases. The high incidence of antibiotic resistance and unprotected wound lesions severely hindered the current therapeutical efficiency. In this study, an antibacterial nanocomposite PAMAM-PLL@AuNPs was designed to avoid antibiotic resistance, and a lyotropic liquid crystal system was used for local drug delivery and protecting lesions. The PAMAM-PLL was constructed with polyamide amine (PAMAM) as the core and polylysine (PLL) as the branch chain, which increased the antibacterial activity by 4 times. After being connected to gold nanoparticles (AuNPs), a further 2 times antibacterial activity improvement was achieved. PAMAM-PLL@AuNPs could eliminate bacteria by multimodal mechanisms, including causing leakage of intracellular substances, inducing intracellular reactive oxygen species and inhibiting bacterial metabolism. Thanks to their spontaneous phase transition and the mechanical response characteristics of the lattice structure, lyotropic liquid crystal with self-healing characteristics was employed to load PAMAM-PLL@AuNPs. The unique structure facilitated buffering external forces and accelerated wound healing. The excellent antibacterial and wound healing properties of the lyotropic liquid crystal drug delivery system were confirmed by a surgical incision infection model. This study is expected to provide a robust strategy for the treatment of SISSIs.

Bismuth-magnesium-oxide-based graphene oxide hybrid film for liquid crystal device application

Hybrid films containing bismuth magnesium oxide (BiMgO) and graphene oxide (GO) are investigated in this study. Solution-processed brush coating is used to fabricate the hybrid films, with the graphene oxide weight ratios adjusted to 0, 5, and 15%. The hybrid films show more stable and higher optical transmittances than the pure BiMgO film. A directional micro/nanogroove structure is observed on the hybrid film surface, which is derived from the shear stress during the brush-coating process; this anisotropic structure is used as a uniform liquid crystal (LC) alignment layer. Uniform and homogeneous LC alignment is then demonstrated via polarized optical microscopy and pretilt angle analyses, along with perfect light-control performance. Enhanced LC polar anchoring energy and hysteresis-free characteristics are observed for the brush-coated hybrid film as the GO-doping concentration is increased. Based on this perspective, the BiMgO-based GO hybrid film achieved via brush coating has potential for applications in next-generation LC systems.

A Single-Enantiomer Emitter Enabled Superstructural Helix Inversion for Upconverting and Downshifting Luminescence with Bidirectional Circular Polarization.

The helical twisting tendency of liquid crystals (LCs) is generally governed by the inherent configuration of the chiral emitter. Here, we introduce the multistage inversion of supramolecular chirality as well as circularly polarized luminescence (CPL) by manipulating the ratio of single enantiomeric emitters (R-PCP) to LC monomers (5CB). Increasing the content of R-PCP from 1 wt % to 3 wt % inverted the helix of LCs from left-handed to right-handed, accompanying a CPL sign changed from positive to negative. The biaxiality of chiral emitters, as well as the steric effect of chiral-chiral and chiral-achiral interaction, were identified as the reasons for helical sense inversion. Due to the strong helical twisting power, 4 wt % R-PCP drove the photonic band gap (PBG) of chiral LCs to match up with their emission range, leading to an inversion of the CPL again with a high dissymmetry factor (≈1.2). Directly adjusting the PBG using chiral emitters is seldom achieved in cholesteric LCs. On this basis, an achiral sensitizer PtTPBP was assembled into the helical superstructure. The generation of triplet-triplet annihilation-induced upconverted CPL from R-PCP and the downshifting CPL from PtTPBP with opposite rotation was achieved in a single chiral LC system by tuning the position of the PBG.

Dielectric characterization of polymer dispersed liquid crystal film with chitosan biopolymer

Polymer Dispersed Liquid Crystals (PDLC) systems were obtained using chitosan as a biopolymer matrix and the nematic liquid crystal (LC) mixture E7 in various concentrations (30, 40 and 50% E7 in chitosan). Several techniques were used to analyze the obtained films: polarizing optical microscopy (POM), IR spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric spectroscopy (DS). FTIR spectroscopy revealed minor changes for all PDLC films, suggesting weak interactions between LC and chitosan matrix. For each sample a clear segregation of the nematic droplets could be observed by POM. DSC measurements show that the phase transitions have shifted to lower temperature values for PDLC samples with approximately 2.7 °C compare to pure E7. The values of α (fraction of LC in the droplets) for compositions of 30, 40 and 50 wt% E7 in Chitosan were 0.48, 0.55 and 0.61 respectively, that are lower than for E7/PMMA system.The qualitative and quantitative analysis of the permittivity spectra obtained by DS reveals the fact that there are no significant changes in the molecular dynamics attributed to pure LC E7 compared to the PDLC composites, leading to the conclusion of the existence of a weak interaction between the two components, fact confirmed by the findings from the FTIR results.