Alignment Of Liquid Crystal Molecules Research Articles

Using image analysis techniques to enhance TFT-LCD manufacturing yield through timely detection of PI alignment layer defects

This study aims to develop a solution to the manufacturing process defects of thin-film transistor liquid crystal display (TFT-LCD) panels. Specifically, it focuses on online image analysis for detecting uneven coatings of the polyimide (PI) alignment layers, which are crucial in the TFT-LCD manufacturing process. The PI solution is typically applied to a substrate surface using an array of nozzles via droplet deposition. During this process, nozzle clogging can cause a series of defects in the form of spots on the alignment layer. These defects impact the alignment of liquid crystal molecules in the TFT-LCD, leading to decreased display quality, reduced visibility, uneven brightness, and compromised image details. If suspected signs of alignment layer spots are identified, the image analysis technology assists online inspectors with prompt responses to minimize TFT-LCD production errors. The results of this study demonstrate timely detection of alignment layer spots, prevention of their progression, and significant reduction of the time required for manual inspection to improve manufacturing yield. This newly developed approach is applicable to not only TFT-LCD production monitoring but also smart display panel manufacturing, thereby providing significant value in high-volume and large-area panel fabrication processes.

A food safety gadget for acrylamide determination: Aptamer placement at surfactant-liquid crystal interface

A tag-free and sensitive aptasensor was introduced to quantify acrylamide based on pursuing the directional order of liquid crystal molecules (LCs) at the surfactant-decorated interface. The hydrophobic interaction of surfactant tails and LCs induced their well-ordered vertical design. The regular alignment of LCs was perturbed through the electrostatic interaction of the specific aptamer with the surfactant head, which altered the polarized texture of the aptasensor from dark to bright optical appearance. However, in the presence of acrylamide and its specific interaction with aptamer strand, LCs arranged vertically with a dark polarized texture. Using the designed aptasensor, acrylamide was detected over the ranges of 1 fmol L−1 to 1 nmol L−1 and 1 nmol L−1 to 50 μmol L−1 with the detection limit (LOD) of 0.28 fmol L−1 and the recovery value of 92.36–101.35%. Besides, the aptasensor successfully quantified acrylamide in the diverse real samples including decaffeinated coffee (36 μg kg−1), roasted coffee (159 μg kg−1), roasted date seeds (13–369 μg kg−1) and roasted quince (1556 μg kg−1). Acrylamide content of cocoa and instant date seed powder were less than LOD. The detection methodology described in this study provides a sensitive, facile, rapid and portable tool for LC-based sensing of acrylamide.

Tunable three-dimensional architecture of nematic disclination lines

Disclination lines play a key role in many physical processes, from the fracture of materials to the formation of the early universe. Achieving versatile control over disclinations is key to developing novel electro-optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, we introduce a theoretical framework to tailor three-dimensional disclination architecture in nematic liquid crystals experimentally. We produce quantitative predictions for the connectivity and shape of disclination lines found in nematics confined between two thinly spaced glass substrates with strong patterned planar anchoring. By drawing an analogy between nematic liquid crystals and magnetostatics, we find that i) disclination lines connect defects with the same topological charge on opposite surfaces and ii) disclination lines are attracted to regions of the highest twist. Using polarized light to pattern the in-plane alignment of liquid crystal molecules, we test these predictions experimentally and identify critical parameters that tune the disclination lines' curvature. We verify our predictions with computer simulations and find nondimensional parameters enabling us to match experiments and simulations at different length scales. Our work provides a powerful method to understand and practically control defect lines in nematic liquid crystals.

응답시간이 개선된 액정 기반 능동 반사 배열 안테나 단위 셀 구조

This paper presents a unit cell structure for liquid crystal (LC)-based reconfigurable reflective arrays, aimed at improving the imbalance in response time. Conventional LC-based reflectarray antenna unit cells, which have been widely used as high-gain beam-steerable antennas, have an imbalance in response time because of different alignment of LC molecules during the rise and decay times. By separating the metal layers in contact with the LC layer and applying four bias voltages, we generated both horizontal and vertical electric field. Accordingly, the decay time was improved by unifying the methods in which the LC molecules were aligned during the rise and decay times. Our measurements confirm that the decay time can be reduced to approximately 1/3 compared to the conventional structure, indicating the possibility of resolving the imbalance.

CdSe quantum dots enhancing blue emission of nematic liquid crystals

Herein, we report the enhancement in blue emission of nematic liquid crystals (NLCs) doped with CdSe quantum dots (QDs) at room temperature. CdSe QDs were synthesized by a high temperature wet chemical method. X-ray diffraction pattern suggest zinc blend crystal structure of CdSe QDs without impurity phase formation. The absorption peak and PL emission of QDs is observed at 503 nm and 526 nm respectively. The QDs size is found to be 2.3 nm calculated by excitonic peak. The polarization states of the QD-based NLCs were studied by using polarising optical microscopic (POM) images under crossed geometry of polarizer and analyser. The uniform colour distribution throughout the cell indicates uniform cell thickness with a planar alignment of liquid crystal molecules. Moreover, dark, and bright states of POM images are used to analyse the defects in alignment of NLC molecules. It is worthwhile to note here that the incorporation of QDs in NLCs helps in reducing defects and light leakage centres which further increases the absorption and hence emission of NLCs. The significant enhancement in the PL intensity of the NLC of about 60% upon CdSe QDs doping is observed at room temperature which attributed to the increase in molecular alignment of NLCs composite.

Self-Folding Liquid Crystal Network Filaments Patterned with Vertically Aligned Mesogens.

Fibrous soft actuators with high molecular anisotropy are of interest for shape morphing from 1D to 2D and 3D in response to external stimuli with high actuation efficiency. Nevertheless, few have fabricated fibrous actuators with controlled molecular orientations and stiffness. Here, we fabricate filaments from liquid crystal networks (LCNs) with segmental crosslinking density and gradient porosity from a mixture of di-acrylate mesogenic monomers and small-molecule nematic or smectic liquid crystals (LCs) filled in a capillary. During photopolymerization, phase separation between the small-molecule LCs and LCN occurs, making one side of the filament considerably denser than the other side. To direct its folding mode (bending or twisting), we control the alignment of LC molecules within the capillary, either along or perpendicular to the filament long axis. We show that the direction of UV exposure can determine the direction of phase separation, which in turn direct the deformation of the filament after removal of the small-molecule LCs. We find that the vertical alignment of LCs within the filament is essential to efficiently direct bending deformation. By photopatterning the filament with segmental crosslinking density, we can induce a reversible folding/unfolding into 2D and 3D geometries triggered by deswelling/swelling in an organic solvent. Moreover, by taking advantage of the large elastic modulus of LCNs and large contrast of the modulus before and after swelling, we show that the self-folded LCP filament could act as a strong gripper.

Photo-induced change in alignment of mesogens using reduction of viologens as a trigger

Liquid crystals (LCs), whose refractive index can be changed by light irradiation, can be used as photoresponsive optical materials. In this study, an LC viologen was proposed as a novel photoresponsive compound that induced a change in the alignment of LC molecules (mesogens). An extended viologen with an asymmetric core, that exhibits a low-order LC phase at room temperature, was mixed with the well-known nematic LC compound (5CB) to prepare homogeneously aligned films. The change in the alignment of the mesogens was successfully induced by triggering a one-electron reduction reaction of the viologen moieties by light irradiation.

Quantitative Biosensing Based on a Liquid Crystal Marginally Aligned by the PVA/DMOAP Composite for Optical Signal Amplification.

The working principle for a liquid crystal (LC)-based biosensor relies on the disturbance in the orderly aligned LC molecules induced by analytes at the LC-aqueous or LC-solid interface to produce optical signals that can be typically observed under a polarizing optical microscope (POM). Our previous studies demonstrate that such optical response can be enhanced by imposing a weak electric field on LCs so that they are readily tilted from the homeotropic alignment in response to lower concentrations of analytes at the LC-glass interface. In this study, an alternative approach toward signal amplification is proposed by taking advantage of the marginally tilted alignment configuration without applying an electric field. The surface of glass substrates was modified with a binary aligning agent of poly(vinyl alcohol) (PVA) and dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP), in which the amount of PVA was fine-tuned so that the interfacing LC molecules were slightly tilted but remained virtually homeotropically aligned to yield no light leakage under the POM in the absence of an analyte. Two nematic LCs, E7 and 5CB, were each sandwiched between two parallel glass substrates coated with the PVA/DMOAP composite for the detection of bovine serum albumin (BSA), a model protein, and cortisol, a small-molecule steroid hormone. Through image analysis of the optical appearance of E7 observed under the POM, a limit of detection (LOD) of 2.5 × 10−8 μg/mL for BSA and that of 3 × 10−6 μg/mL for cortisol were deduced. Both values are significantly lower than that obtained with only DMOAP as the alignment layers, which correspond to signal amplification of more than six orders of magnitude. The new approach for signal amplification reported in this work enables analytes of a wide range of molecular weights to be detected with high sensitivity.

Physicochemically modified anisotropic polyacrylamide thin film via ion‐beam treatment for liquid crystal system

AbstractWe investigated ion‐beam (IB)‐treated polyacrylamide (PAM) film as a liquid crystal (LC) alignment layer. Polarized optical microscopy and pretilt angle analysis show the uniform LC alignment status. Atomic force microscopy shows the IB etching effect, and X‐ray photoelectron spectroscopy indicates the formation of carbon–oxygen bonds on the surface, which ensured the uniform alignment of LC molecules via van der Waals forces interaction. The reformed PAM films also had good thermal budgets and optical transparency for the LC system. The IB‐treated PAM films demonstrated stable electro‐optical performances in a twisted nematic LC system. Hence, IB treatment can be an effective method to apply several polymer materials to the LC alignment layer, and IB‐irradiated PAM films have remarkable potential for use in the LC system.

Thermotropic liquid crystals in the detection of albumins through a microscopic, spectroscopic and computational approach

Liquid crystals (LCs) are a promising system of molecules for biosensing as a transducing agent for detecting protein human serum albumin (HSA). Herein, we investigate the detection of HSA by a liquid crystal 4′-octyl-4-biphenylcarbonitrile (8CB) intending to develop an LC-based biosensor. The change in the alignment of liquid crystal molecules in the presence of protein results in the transfigurations of the director through interactions. The limit of 8CB to detect HSA is found to be at a reliable concentration in the development of biosensors. The transition in the director configurations from radial to bipolar during the crystalline to the isotropic phase of the liquid crystals are studied under polarizing optical microscopy. These transitions confirm the detection of HSA by 8CB. The docking analysis depicts the interactions by which 8CB liquid crystal molecules bind with protein HSA. The binding energy, binding active residues and their distances between the docked residues of HSA and molecules of ligand 8CB are calculated by molecular docking. Temperature-dependent Raman spectroscopy is used to analyse the spectral behaviour of the interactions. The residues validated by molecular docking studies correlate well with the findings of Raman spectra for the interaction between 8CB and HSA.

Interactions investigated by the spectroscopic, microscopic and molecular docking studies for liquid crystal-based biosensor

ABSTRACT The interactions between liquid crystal (LC) 4´-pentyl-4-biphenylcarbonitrile and protein bovine serum albumin are investigated to develop an LC-based biosensor. Various techniques, such as polarising optical microscopy, Raman spectroscopy, and molecular docking method, are used for analysing these interactions. The change in the alignment of LC molecules in the presence of bovine serum albumin results in the director configuration transition. This transfiguration of the director of LC molecules, when it undergoes a change from radial to bipolar configuration, confirms the detection of albumins under polarising optical microscopy. The limit of detection is also determined from this study. The Raman spectra are deconvoluted to calculate the spectral parameters, namely peak position, linewidth, and integrated intensity. The variation of these parameters with concentration and temperature is discussed, pertaining to the changes in orientational ordering and inter/intramolecular interactions. The active binding sites, active residues and binding energy are calculated by molecular docking analysis. The active binding residues of albumins involved in the docking with liquid crystal are further confirmed using Raman spectroscopy.

Inch-scale graphene-based LC tunable phase retarders: Experimental study of surface interaction between liquid crystal-polyimide-graphene layers

Recently Liquid Crystal (LC) devices open new route for the next generation optical elements revealing on novel materials that come to a scene, among which graphene endorse amazing capabilities. Herein, we perform detailed study of the surface interaction between LC molecules, graphene (single and multilayer) and alignment layer during assembling tunable LC phase retarders on arbitrary substrates. By considering the surface free energy of graphene a proper selection of polyimide (PI) as a polar layer for non-contact planar alignment of LC molecules is presented. Surface anchoring energy and pre-tilt angle value have been determined to characterize the interfaces at the boundary and their impact on the dynamic performances of assembled LC devices. Besides the excellent phase modulation repeatability over the large-scale area of retrofitted LC structures, an electrically tunable LC phase retarder supported by graphene on PDMS substrate that exhibits great potential for future ITO-free integrated photonic devices and bio-oriented technologies is demonstrated.

Enhanced Bandwidth Broadening of Infrared Reflector Based on Polymer Stabilized Cholesteric Liquid Crystals with Poly(N-vinylcarbazole) Used as Alignment Layer

Alignment layer plays a critical role on liquid crystal (LC) conformation for most LC devices. Normally, polyimide (PI) or polyvinyl alcohol (PVA), characterized by their outstanding thermal and electrical properties, have been widely applied as the alignment layer to align LC molecules. Here, we used a semi-conductive material poly(N-vinylcarbazole) (PVK) as the alignment layer to fabricate the cholesteric liquid crystal (CLC) device and the polymer-stabilized cholesteric liquid crystals (PSCLC)-based infrared (IR) reflectors. In the presence of ultraviolet (UV) irradiation, there are hole–electron pairs generated in the PVK layer, which neutralizes the impurity electrons in the LC–PVK junction, resulting in the reduction in the built-in electric field in the LC device. Therefore, the operational voltage of the CLC device switching from cholesteric texture to focal conic texture decreases from 45 V to 30 V. For the PSCLC-based IR reflectors with the PVK alignment layer, at the same applied electric field, the reflection bandwidth is enhanced from 647 to 821 nm, ranging from 685 to 1506 nm in the IR region, which makes it attractive for saving energy as a smart window.

Uniformly aligned liquid crystal molecules on reformed poly(ethylene-co-vinyl acetate) layers driven by ion beam exposure

ABSTRACT The characteristics of a poly(ethylene-co-vinyl acetate) (PEVA) film formed by spin coating process and ion beam (IB) irradiation was investigated with irradiation times. A physicochemical analysis was used to analyse the suitability of the PEVA film as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy (AFM) revealed an increased surface roughness after IB irradiation. X-ray photoelectron spectroscopy (XPS) analysis showed IB irradiation broke the polymer branches and increased the oxygen concentration and bonding on the surface. These derived the strong Van der Waals forces and dipole-dipole interactions between the PEVA surface and LCs. The IB irradiation generated surface anisotropy on the PEVA film and unidirectional LC alignment was achieved. Polarised optical microscopy (POM) and pre-tilt angle measurements were carried out to show the uniform LC alignment. The transmittance curve exhibited a high optical performance. These results show the promising capabilities of IB irradiated PEVA film as an alignment layer in LC displays.

Vertical Alignment of Liquid Crystals on Comb-Like Renewable Chavicol-Modified Polystyrene.

This study demonstrates liquid crystal (LC) alignment behaviors on the surface of phytochemical-based and renewable chavicol-modified polystyrene (PCHA#, # = 20, 40, 60, 80, and 100, where # represent the molar content of chavicol moiety in the side group) via polymer modification reactions. Generally, a LC cell fabricated with a polymer film containing a high molar content of the chavicol side group exhibited a vertical LC alignment property. There is a correlation between the vertical alignment of LC molecules and the polar surface energy value of the polymer films. Therefore, vertical LC alignment was observed when the polar surface energy values of these polymer films were smaller than about 1.3 mJ/m2, induced by the nonpolar chavicol moiety having long and bulky carbon groups. Aligning stability under harsh conditions such as ultraviolet (UV) irradiation of about 5 J/cm2 was observed in the LC cells fabricated from PCHA100 film. Therefore, it was found that the plant-based chavicol-substituted polymer system can produce an eco-friendly and sustainable LC alignment layer for next-generation applications.

Potential liquid crystal-based biosensor depending on the interaction between liquid crystals and proteins

Liquid crystal biosensors serve an essential role to detect biomolecules and chemical events as an effective, simple and early detection tool. The detection of Human serum albumin protein by a room temperature liquid crystal 4́-pentyl-4-biphenylcarbonitrile has been investigated using multiple techniques such as Polarizing optical microscope, Raman spectroscopy and molecular docking. The dynamics of director transfigurations of the liquid crystal molecule in the presence of protein through interactions are reported in the study. The change in the alignment of liquid crystal molecules during the nematic phase is observed under a polarizing optical microscope. The interactions through which the liquid crystal molecules bind with protein is depicted from the docking analysis. The residues in the active sites confirm their presence from docking studies. The spectral behaviour has been investigated by temperature-dependent Raman spectroscopy. The findings from Raman spectra for the interaction between these compounds correlates with the residues confirmed from molecular docking analysis.

Electrically Controlled Liquid Crystal Microlens Array Based on Single-Crystal Graphene Coupling Alignment for Plenoptic Imaging.

As a unique electric-optics material, liquid crystals (LCs) have been used in various light-control applications. In LC-based light-control devices, the structural alignment of LC molecules is of great significance. Generally, additional alignment layers are required for LC lens and microlens, such as rubbed polyimide (PI) layers or photoalignment layers. In this paper, an electrically controlled liquid crystal microlens array (EC-LCMLA) based on single-crystal graphene (SCG) coupling alignment is proposed. A monolayer SCG with high conductivity and initial anchoring of LC molecules was used as a functional electrode, thus no additional alignment layer is needed, which effectively simplifies the basic structure and process flow of conventional LCMLA. Experiments indicated that a uniform LC alignment can be acquired in the EC-LCMLA cell by the SCG coupling alignment effect. The common optical properties including focal lengths and point spread function (PSF) were measured experimentally. Experiments demonstrated that the proposed EC-LCMLA has good focusing performance in the visible to near-infrared range. Moreover, the plenoptic imaging in Galilean mode was achieved by integrating the proposed EC-LCMLA with photodetectors. Digital refocusing was performed to obtain a rendering image of the target.

Multi-Functional Film Based on Aligned CNT Sheet for Liquid Crystal Display Application

Carbon nanotube (CNT), an extremely long hollow cylinder with nanometer-sized diameter, is a promising carbon material with unique thermal, electrical, and physical properties. Due to their peculiar and fascinating properties, CNTs have been studied and used in various industries since their discovery. The CNTs are potentially viable alternatives for conventional materials in electric devices considering their mechanical resilience, high electrical conductivity, and optical transparency. The alignment of CNTs into ordered structures garnered a special interest as it enhances electrical conductivity and optical transparency, and generates a new intriguing anisotropic optical absorption property. The optical properties of highly oriented CNT sheets have been investigated to apply as optical polarizer and polarized light source. Further, the flexible electrodes derived from an aligned CNTs have unveiled applications in super-capacitors, solar cell, and lithium-ion battery. Therefore, to utilize CNTs in LCD and many other flexible electronic device applications it is essential to attain highly ordered CNTs which should be static even under external stresses such as bending, pressing, and strain.In this work, we fabricated the aligned CNT sheet films (a-CSFs) in which the grown CNTs are stretched unidirectionally on the substrate and its orientation is fixed via polymerization of a coated monomer and then measured its optical and mechanical properties, testing feasibility of its application for multi-functioning films such as polarizer, electrode, and liquid crystal (LC) alignment. The fabricated a-CSF exhibits polarization efficiency (PE) (87.23% of 10 layers of a-CSF), sheet resistance (361.7 Ω/sq), and an excellent aligning capability of LC molecules as shown in Fig. 1 (a~c). Besides, flexibility and stability test of a-CSF via repeating bending test of 1,000 cycles at bending radius of 2 mm exhibited very low variation in the change ratio of sheet resistance and transmittance less than 8% and 10%, respectively.Utlilizing the mutifunctionalty of a-CSF, a liquid crystal display (LCD) with a twisted nematic(TN) mode was fabricated and exhibited feasibility of dynamic swicthing between bright and dark states on application of voltage off/on even without using conventional components of LCD such as transparent electrode, film-type polarizer, and polyimide-type alignment layer. We measured the voltage-dependent transmittance of both devices based on the a-CSF with 5 layers and 8 layers. The threshold voltage (Vth) and operating voltage (Vop) are defined as the voltage required to achieve 90% and 10% of transmittance relative to maximum transmittance, respectively. The measured Vth of both devices with 5 and 8 layers are 1.7 Vrms and 1.3 Vrms, respectively and the measured Vop of both devices are 7.6 Vrms and 4.3 Vrms, respectively. In the case of 8 layers, it shows slightly lower Vth and Vop, which is mainly due to the lower sheet resistance of a-CSF with 8 layers than 5 layers as shown Fig 2.In conclusion, we fabricated the multi-functional a-CSF with properties of the electrode, polarizer, and alignment layer based on the a-CSF using the simple fabrication process. We confirmed the a-CSFs exhibit better conductivity and PE in the visible regime. Furthermore, it has the excellent grooved morphology along the drawn direction of a-CS for homogeneous alignment of LC molecules. We carried out the bending test to confirm the stability of the films from mechanical stress. It showed excellent stability after bending tests of 1,000 cycles. The performance of the fabricated TN cells using a-CSFs were considerably working good. Figure 1

A new approach for directional homogeneous alignment of liquid crystals using electric field-guided orientation of nonionic amphiphiles

Conventional homogeneous alignment of liquid crystals (LCs) utilizes rubbed or photo-aligned polyimide surfaces that determine the molecular orientation of LCs along in-plane direction. However, this alignment method based on polymeric layer requires complicated layer forming processes and considerable synthetic effort for special functional polyimides. In this study, a simple and unprecedented directional alignment approach has been developed to horizontally align nematic LCs using electric field-guided orientation of nonionic amphiphiles, spontaneously forming nanoscale supramolecular thin layer on the indium tin oxide substrate via hydrogen bonding. The in-plane electric field between simple slit electrodes induced the horizontal orientation of the anchored amphiphilic molecules parallel with electric field. Furthermore, the subsequent immobilization of inclined amphiphiles along a directional electric field through photopolymerization of common mesogenic diacrylates within LC medium resulted in a new type of homogenous alignment layer with a well-defined orientation direction for LCs. The proposed facile alignment methodology using small quantities of nonionic amphiphiles and mesogenic diacrylates afforded uniform and stable planar alignment of LC molecules with the controlled director. This novel alignment approach is expected to find a wide range of potential applications involving LC displays, optically patterned retarders, biosensors, and electronic lenses.

66‐3: The Way to Improve Black Circle Mura in Curved Display by Polyimide‐less Technology

In the fabrication of curved diplay, there always exist black circle mura, which is induced by the curvature. To improve this phenomenon, polyimide‐less technology was introduced. Polyimide‐less technology is a technology in which an additive can replace polyimide film to align LC molecules. In this technology, the additive added in liquid crystal (LC) host can not only align the LC molecules, but also have different pretilt angle generation ratio compared with PI film. In this paper, we fabricated curved panels using CF substrate with PI and TFT substrate without PI.The additive in PI‐less liquid crystals could anchor the TFT substrate and align the LC molecules on the TFT side. After UV process, the CF substrate had smaller pretilt angle. And the black circle mura appeared in the curved panel could be solved completely. Then we also studied the alignment, optical and image sticking performance, there existed no difference between the curved panels using PI‐less technology and the curved ones with normal PI layers.