Liquid Crystal Modulator Research Articles

Broadband nonlinear modulation of incoherent light using a transparent optoelectronic neuron array

Nonlinear optical processing of ambient natural light is highly desired for computational imaging and sensing. Strong optical nonlinear response under weak broadband incoherent light is essential for this purpose. By merging 2D transparent phototransistors (TPTs) with liquid crystal (LC) modulators, we create an optoelectronic neuron array that allows self-amplitude modulation of spatially incoherent light, achieving a large nonlinear contrast over a broad spectrum at orders-of-magnitude lower intensity than achievable in most optical nonlinear materials. We fabricated a 10,000-pixel array of optoelectronic neurons, and experimentally demonstrated an intelligent imaging system that instantly attenuates intense glares while retaining the weaker-intensity objects captured by a cellphone camera. This intelligent glare-reduction is important for various imaging applications, including autonomous driving, machine vision, and security cameras. The rapid nonlinear processing of incoherent broadband light might also find applications in optical computing, where nonlinear activation functions for ambient light conditions are highly sought.

Using orientational transition of acetone-doped liquid crystal triggered by vanillin as a naked-eye vanillin sensor

Vanillin is an aromatic organic compound that is widely used in the food and cosmetics industries. The development of a simple and rapid method for the naked-eye detection of vanillin is essential for monitoring the vanillin production process. In this study, liquid crystal 5CB (4-cyano-4’-pentylbiphenyl) is doped with acetone and used as a sensing platform to detect vanillin in alkaline solutions with high specificity for the first time. Before the addition of vanillin, the acetone-doped 5CB adopts a homeotropic orientation and appears dark due to the formation of an electrical double layer (EDL) at the 5CB/water interface. In the presence of vanillin, it forms a complex with acetone inside 5CB, disrupting the EDL and the homeotropic orientation of 5CB. The event leads to a dark-to-bright transition which can be used to quantify the concentration of vanillin in a range between 0.1 and 25 mg/L. The limit of detection (LOD) for the vanillin sensor is 0.06 mg/L. As a proof of concept, the sensor is employed to monitor the vanillin concentration during oxidation of coniferyl alcohol. In the presence of 5000 mg/L of H2O2 and 1 mg/L iron tetraamidomacrocyclic ligand (Fe-TAML), 1750 mg/L of coniferyl alcohol can be converted to 393.0 mg/L of vanillin after a 30-min reaction at room temperature. This study demonstrates potential applications of the acetone-doped liquid crystal sensors for monitoring the production of vanillin under various conditions.

Wide heart-shaped mini-LEDs without a second lens as a large area, ultra-high luminance, and flat light source.

In recent years, the demand for outdoor advertising and industrial display applications has been steadily increasing. Outdoor environments require higher brightness levels, thus requiring a reduction in the thermal resistance of the light source package. However, using secondary optical lenses to decrease the number of light sources is not a suitable solution because it may lead to the issue of lens detachment. Therefore, this paper proposes a packaging structure for wide heart-shaped angular light distribution mini-light emitting diodes (WHS mini-LEDs) with a primary optical design to enhance the light-emitting angle. The chips are directly bonded to an aluminum substrate using the metal eutectic process to minimize thermal resistance in the packaging. The experimental results indicated that the WHS mini-LED package had a total thermal resistance of 6.7 K/W. In a 55-inch backlight module (BLM), only 448 WHS mini-LEDs coupled with a quantum dot (QD) film and a brightness enhancement film (BEF) were required. Each lamp board was operated at 20.5 V and 5.5 A. The average luminance of the liquid crystal module (LCM) can reach 2234.2 cd/m2 with a uniformity of 90% and an NTSC value of 119.3%. This design offers a competitive advantage for outdoor advertising displays and industrial displays that require large areas, high brightness, and high color saturation.

Influence of the length of end-group double bond substituents on the temperature change of phase transition in liquid crystals

ABSTRACT A series of nematic liquid crystal (LC) monomers, containing a reactive group in the lateral substituent, were designed and synthesised through an organic synthesis reaction. Considerable changes were made to the properties of the liquid monomers by varying the terminal alkyl chain lengths. The molecular structures of the intermediates and the LC monomers were characterised by flourier infrared absorption spectrometry and proton nuclear magnetic resonance (1H NMR) spectroscopy, leading to the identification of the target product. The phase transition temperatures of the LC monomers were observed and analysed using differential scanning calorimetry (DSC) and polarising optical microscopy (POM) with a hot stage. The two-way thermotropic liquid crystalline behaviour was observed during the heating process, providing insight into the effect of substituent changes on the phase transition temperature.

Effect of glycerol incorporation on the liquid crystal structure of sucrose fatty acid ester in aqueous solution

A series of homogeneous samples with high sugar-surfactant content (sucrose fatty acid ester/water and sucrose fatty acid ester/glycerol/water systems) were prepared with well-controlled processes and investigated by DSC, polarized microscopy, X-ray scattering and rheology. Meanwhile the accuracy of the preparation process is confirmed gas chromatography. The polarized microscopy indicates that the ordering degree of the network structure composed of the liquid crystals may be reduced by the glycerol addition. The results of DSC revealed that 50% glycerol solution could significantly inhibit the crystallization of sucrose fatty acid ester and resulted in a significant widening of the temperature interval for the transformation of the liquid crystal phase into the gel phase. In order to further evaluate the effect of glycerol molecules versus water molecules on the liquid crystal structure of sucrose fatty acid ester, we comparatively analyzed the X-ray scattering data from two perspectives: the mass fraction and molar fraction. It was found that 50% glycerol solution could inhibit the crystallization of sucrose fatty acid ester through changing the water-head group interaction of surfactant, facilitates the integration of sucrose fatty acid ester with different alkyl chain length and may reduce the regularity of liquid crystal, both from the perspective of surfactant mass and molar fraction. Furthermore, the addition of 50% glycerol (w/w) does not significantly impede the liquid crystal formation of sucrose fatty acid ester in aqueous solution. However, from the perspective of surfactant mass fraction, glycerol incorporation could reduce the effective cross-sectional areas of the hydrophilic part of sucrose fatty acid ester in aqueous solution and induce the phase transition of hexagonal liquid crystals to aggregates with less positive curvature, while an opposite tendency could be obtained from the perspective of surfactant molar fraction. The conclusions are also confirmed by subsequent rheological test. Moreover, the results of rheological measurements reveals that the interactions among cylindrical units of the hexagonal liquid crystalline phase become weaker and the surfactant molecules aggregate more loosely in the cylindrical unit with the glycerol incorporation. Moreover, the above-mentioned influence of glycerol on the liquid crystal structure of sucrose fatty acid ester in aqueous solution would be similar but more prominent from the perspective of the molar fraction.

Anisotropic crystal growth in blue phase I transitioned from a uniformly oriented cholesteric phase.

Phase transitions in blue phase liquid crystals (BPLCs) have attracted significant attention from the technical perspective of BP orientation control and the theoretical perspective of analogs with crystalline solids. The phase transition phenomena in BPs significantly depend on the phase state before the transition. In this study, we focused on the cholesteric (Ch)-BPI phase transition and found that BPI crystals exhibited a square shape upon the phase transition from the uniformly oriented Ch phase to the BPI phase. This square crystal shape was common across three BPLC materials with different elastic constants, and the shape reflected the crystal axis. The in-plane crystal orientation correlates with the easy axis on the substrate surface, suggesting that the [011] axis tends to coincide with the easy axis. However, the easy axis has little effect on the crystal growth rate. Furthermore, scratches on the substrate surface promoted nucleation. Based on this behavior, it was demonstrated that the nucleation position and density could be controlled by intentionally disturbing the Ch orientation by locally changing the easy axis using photoalignment. This study focused on the anisotropic crystal growth of BPI, providing interesting insights into LC phase transitions and soft matter crystal growth. In addition, it offers techniques for the fabrication of large BPI crystals, contributing to the enhanced electrical and optical performances of BPLC devices.

Orientational transitions of discotic columnar liquid crystals in cylindrical pores.

Confined in a cylindrical pore with homeotropic anchoring condition, the hexagonal columnar phase of discotic liquid crystals can form a "log-pile" configuration, in which the columns are perpendicular to the long axis of the pore. However, the {100} planes of the hexagonal lattice can orient either parallel (termed (100)‖ orientation) or perpendicular ((100)⊥) to pore axis. Here we experimentally show that the (100)‖ orientation is found in narrower cylindrical pores, and the (100)‖-(100)⊥ transition can be controlled by engineering the structure of the molecules. The (100)‖ orientation is destroyed in asymmetric discotics hepta(heptenyloxy)triphenylene (SATO7); replacing the oxygen linkage in hexa(hexyloxy)triphenylene (HATO6) by sulphur (HATS6) improves the (100)‖ orientation in small pores; adding a perfluorooctyl end to each alkyl chain of HATO6 (HATO6F8) moves the (100)‖-(100)⊥ transition to larger pores. We have provided a semi-quantitative explanation of the experimental observations, and discussed them in the context of previous findings on related materials in a wider pore size range from 60 nm to 100 μm. This allows us to produce a comprehensive picture of confined columnar liquid crystals whose applications critically depend on our ability to align them.

Possibilities and limitations of convolutional neural network machine learning architectures in the characterisation of achiral orthogonal smectic liquid crystals.

Machine learning is becoming a valuable tool in the characterisation and property prediction of liquid crystals. It is thus worthwhile to be aware of the possibilities but also the limitations of current machine learning algorithms. In this study we investigated a phase sequence of isotropic - fluid smecticA - hexatic smectic B - soft crystal CrE - crystalline. This is a sequence of transitions between orthogonal phases, which are expected to be difficult to distinguish, because of only minute changes in order. As expected, strong first order transitions such as the liquid to liquid crystal transition and the crystallisation can be distinguished with high accuracy. It is shown that also the hexatic SmB to soft crystal CrE transition is clearly characterised, which represents the transition from short- to long-range order. Limitations of convolutional neural networks can be observed for the fluid to hexatic SmA to SmB transition, where both phases exhibit short-range ordering.

Aquatic Functional Liquid Crystals: Design, Functionalization, and Molecular Simulation.

Aquatic functional liquid crystals, which are ordered molecular assemblies that work in water environment, are described in this review. Aquatic functional liquid crystals are liquid-crystalline (LC) materials interacting water molecules or aquatic environment. They include aquatic lyotropic liquid crystals and LC based materials that have aquatic interfaces, for example, nanoporous water treatment membranes that are solids preserving LC order. They can remove ions and viruses with nano- and subnano-porous structures. Columnar, smectic, bicontinuous LC structures are used for fabrication of these 1D, 2D, 3D materials. Design and functionalization of aquatic LC sensors based on aqueous/LC interfaces are also described. The ordering transitions of liquid crystals induced by molecular recognition at the aqueous interfaces provide distinct optical responses. Molecular orientation and dynamic behavior of these aquatic functional LC materials are studied by molecular dynamics simulations. The molecular interactions of LC materials and water are key of these investigations. New insights into aquatic functional LC materials contribute to the fields of environment, healthcare, and biotechnology.

AN OVERVIEW ON CUBOSOMES AS REMARKABLE NANOCARRIER FOR DRUG DELIVERY

Lipids have been extensively used as main ingredients in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers and lipid-based lyotropic liquid crystals. Over the past few years, lipid-based lyotropic, bicontinuous cubic phase liquid crystals have been investigated for their applicability to controlled delivery of active ingredients. Lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The emulsification of cubic lipid phases in water results in the production of cubosomes that can be defined as nanoparticulate disperse systems characterised by high biocompatibility and bioadhesivity. The unique microstructure of cubosomes have the potentials to control the release of active ingredients, improve drug bioavailability and reduce toxicity, enhance the stability of drugs and to increase the penetrability of drug after topical application. This reflection will provide an overview of the lipids used to prepare cubic phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic phase as drug delivery systems and its applications will be discussed. It might act as smart lipid nanoparticles for drug delivery.

Design of liquid crystal-aqueous interface for detection of calcium ions using protein as recognition probe

ABSTRACT The advancement of liquid crystal (LC)-based biosensing platform for understanding the interactions of adsorbed proteins with lipid-designed LC-aqueous interface has significant scientific interest due to its point-of-care diagnostic applications and fundamental biological research. The ordering transition of LCs at 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) decorated LC-aqueous interface was examined to observe the biosensing of a physiologically important Ca2+ signalling protein recombinant human calmodulin (CaM). Self-assembled POPC molecules promote homeotropic anchoring of LC at the LC-aqueous interface with dark optical appearance under crossed polarizers. Interestingly, the optical state of LC changed to planar (bright optical appearance) when CaM was in the proximity of lipid adsorbed LC-aqueous interface, indicating label-free detection of CaM at those interfaces. It was further observed that the POPC decorated LC-aqueous interface is specific for the detection of CaM protein among other amphiphiles (LPA, DLPC, CTAB and SDS) decorated LC-aqueous interfaces tested. The sensitivity of the POPC decorated LC-aqueous interface towards the detection of CaM was observed in the nanomolar regime (~150 nM). CaM is a Ca2+ binding protein; hence, the CaM-POPC decorated LC-aqueous interface was further utilized for the detection of Ca2+. Interaction of CaM with Ca2+ increases the α-helical content of CaM, which results in the reorganization of POPC molecules at the LC-aqueous interface and leads to the homeotropic orientation of LC with a dark appearance under crossed polarizer. Compared to other spectroscopic/biological techniques, the LC-based system is easy to handle due to its simple label-free optical data, high sensitivity, cost-effectivity and low sample requirement.

Dynamical behaviour of phase transitions in liquid crystals under ultrasound field

The study investigates the influence of an acoustic field on the process of interface formation, phase boundary propagation kinetics, and isotropic phase nucleation in a nematic liquid crystal (NLC) during the NLC → isotropic liquid (IL) phase transition. Experimental studies were conducted using acoustically "rigid" drops and both "rigid" and "soft" cells of sandwich type, with one substrate being a piezo quartz’s X-cut plate. The thickness of the investigated LC layers with planar and homotropic orientations was 20, 50, and 100 μm. The frequency of the ultrasonic field ranged from 3.77 to 4 MHz. Additionally, we computed the values of isotropic germ’s radius in NLC during the NLC → IL phase transition both without and under the ultrasonic field. The obtained data indicate an increased probability of forming a germ of an isotropic phase during the NLC → IL phase transition under the influence of ultrasound. These findings align well with the experimentally observed trends in the changes of phase transition temperature, specifically with the depression of the NLC → IL phase transition temperature in the presence of an ultrasound field.

Frequency suppression of director oscillations in AC-driven liquid-crystal-based terahertz phase shifters.

Frequency-induced instability is widely present in nematic liquid crystals (LCs), which poses a problem in improving liquid-crystal-based phase-shift devices driven by alternating currents. Herein, the Fréedericksz transition of thick nematic LCs was investigated under alternating electric fields to reveal the suppression of frequency-induced instability in the low frequency range. By extending the Frank-Leslie equation to the AC-driven case, the response of the LC was numerically calculated, and the frequency threshold for suppressing the driven instability was estimated in conjunction with the perturbation method. Experimentally, the frequency suppression of LC fluctuations was verified by using applied electric fields. In addition, the root-mean-square-error of the refractive index was measured to be less than 2 × 10-5, which excludes the convective instability-generating domains in devices. It was revealed that the fabricated thick LC phase shifters provided a phase shift of more than 360° at 2 THz and can be used in the terahertz band. It was observed that the electrically driven phase-shift characteristics were in accordance with the theoretical results as the threshold frequency condition was satisfied. This work provides an experimental and theoretical reference for improving modulation performance and enhancing the characterization of AC-driven LC-based phase-shift devices.

Hyper Thermostability and Liquid-Crystal-Like Properties of Designed α-Helical Peptide Nanofibers.

Structural and thermodynamic transitions of artificially designed α-helical nanofibers were investigated using eight peptide variants, including four peptides with amide-modified carboxyl termini (CB peptides) and four unmodified peptides (CF peptides). Temperature-dependent circular dichroism spectroscopy and differential scanning calorimetry showed that CB peptides exhibit thermostability up to 50 °C higher than CF peptides. As a result, one of the denaturation temperatures approached nearly 130 °C, which is exceptionally high for a biomacromolecule. Thermodynamic analysis and microscopy observations also showed that CB peptides undergo a thermal transition similar to the phase transition in liquid crystals. In addition, one of the peptides showed a sharp and highly cooperative transition with a small enthalpy change at around 25 °C, which was ascribed to a giga-bundle burst of the molecular assembly. These macroscopic changes in the thermostability and crystallinity of CB peptides may be attributed to an increased amphiphilicity of the molecule in the direction of the helix axis, originating from the microscopic modification of the carboxyl-terminus.

Holographic Encryption of Color Video Stream with 4k Resolution Using Phase Liquid Crystal Light Modulators

Holographic Encryption of Color Video Stream with 4k Resolution Using Phase Liquid Crystal Light Modulators

Uniaxial - biaxial lyotropic cholesteric phase transition of lyotropic liquid crystals

ABSTRACT A Landau model is proposed to describe the uniaxial – biaxial lyotropic cholesteric phase transition of lyotropic liquid crystals (LLC). The model free energy is based on a mixture of rod-shaped and disc-shaped micelles. The possibility of the existence of two biaxial lyotropic cholesteric phases and two uniaxial lyotropic cholesteric phases of LLC is discussed. The phase transitions between two biaxial lyotropic cholesteric phases and two uniaxial lyotropic cholesteric phases are explored. Qualitative comparisons between theoretical predictions and recent experimental results are discussed.

A liquid crystal-based sensor exploiting the aptamer-mediated recognition at the aqueous/liquid crystal interface for sensitive detection of serotonin.

We report here a liquid crystal (LC)-based sensor for detecting serotonin (5-HT); the proposed sensor uses target-specific aptamer recognition at a cationic surfactant decorated-aqueous/LC interface. Our detection strategy focuses on the orientational transition of LCs upon biological interactions at the interface. In this sensing system, the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) forms a self-assembled monolayer at the aqueous/LC interface and triggers the homeotropic orientation of LCs. After introducing the 5-HT specific aptamer, an electrostatic attraction occurs between the cationic CTAB and anionic aptamer. This interaction destructs the surfactant monolayer at the interface, inducing reorganization of LC alignment from homeotropic to tilted conditions. In the increasing 5-HT levels, specific binding between 5-HT and the aptamer diminishes the interaction between the aptamer and CTAB, thereby maintaining the homeotropic alignment of LCs. The orientational transition of the LCs was observed under a polarized optical microscope. The developed biosensor has a linear detection range from 1 to 1000nM and a detection limit of 1.68nM. Moreover, the sensor was applied to a human urine sample and a detection limit of 2.25nM was obtained. Overall, the designed LC-based sensor is a sensitive, simple, cost effective, and selective platform for detecting 5-HT in aqueous solutions.

Machine learning-assisted MD simulation of melting in superheated AlCu validates the Classical Nucleation Theory

The validity of the Classical Nucleation Theory (CNT), the standard tool for describing and predicting nucleation kinetics in metastable systems, has been under scrutiny for almost a century. While the CNT is commonly employed to describe liquid → crystal and liquid ↔ vapor phase transitions, its application to the crystal → liquid case has been limited because of the experimental challenges in achieving superheating states and detecting homogeneous liquid nucleation. In this study, we performed comprehensive molecular dynamics (MD) simulations of spontaneous melting of a superheated AlCu crystal under atmospheric pressure at five temperatures, covering a superheating range of T/TL = 1.1–1.3, where TL is the liquidus temperature. Two realistic AlCu models were investigated: one described by the modified embedded atom method (MEAM) and the other by an interatomic potential generated by an artificial neural network machine learning (ML) approach, extensively trained on an ab initio dataset of liquid and crystal configurations. Fifty independent melting events were simulated at each temperature. By analyzing the distribution of melting times using the Poisson law, the homogeneous nucleation rate was determined through the mean lifetime method. Additionally, the Zeldovich factor, critical nucleus size, and work of formation were obtained using the mean first-passage time method, utilizing the disorder parameter based on atomic displacements (liquid-like atoms in the superheated crystal) as the reaction coordinate. Also, the effective atomic transport coefficient across the metastable crystal/critical liquid nucleus interface was determined by MD simulations as the interfacial attachment coefficient for nuclei growth rates. Using these simulation-generated data, the theoretical nucleation rates were calculated by the CNT with no fitting parameters. We found excellent agreement between the theoretically and MD-computed liquid nucleation rates for both MEAM and ML crystals. Notably, the effective solid-liquid interfacial free energy value obtained from the MD data aligns with its recent experimental measure. Moreover, the CNT qualitatively and quantitatively described the underlying details of liquid drop nucleation in our ML solid, unprecedentedly and accurately reproducing the kinetic prefactor and the size, formation energy, and growth rate of the critical nuclei. Thus, the melting of the AlCu model created through machine learning-processed quantum calculations, that is, not relying on hand-crafted interatomic potential functions, was successfully described by the CNT phenomenological formalism, without any adjustable parameters. This finding confirms the CNT as a very reliable descriptor of homogeneous nucleation in the superheated AlCu alloy and generalizes this theory as a powerful tool for analyzing and predicting the kinetics of crystal-liquid transitions.

Effects of quenching temperature on threshold, driving voltage and morphology of reverse mode liquid crystal gel films

This study demonstrated that the electro-optical properties and morphology of reverse mode liquid crystal (LC) gel films are strongly influenced by the quenching temperature (TQ) during the manufacturing processes. Composite films were self-assembled using LC and gelator molecules by using different TQ values (70, 80, 90, 100, 110 and 120 °C) and a cold brine (−15 °C). As TQ increased, the morphology of the gel in the polarised light microscope images are changed from neatly arranged fibre-like patterns to random disordered networks. Furthermore, the threshold and driving voltages of the films decreased. For further investigating the gelation processes, Steady cooling rates of 3, 10 and 30 °C min−1 were adopted during the manufacturing process of the LC films. The corresponding morphologies of the films were carefully inspected and compared with those of the quenched films.

Shape morphing liquid crystal polymers.

Liquid crystal polymers are a type of representative material combining the order-disorder transition of liquid crystals and the superior properties of polymers. The phase transition from the liquid crystal phase to the isotropic state of mesogens causes large, controllable, and reversible deformation of polymers; thus, liquid crystal polymers have emerged as one of the most valuable candidates for shape morphing materials. Much research effort is dedicated to liquid crystal polymers for shape morphing that are designed to develop more novel applications. Therefore, this review aims to summarize the recent development of shape morphing materials based on liquid crystal polymers.