Liquid Crystal Texture Research Articles

Effect of smectic polymers on cholesteric liquid crystals.

Composite materials made of polymers and liquid crystals have been widely employed in smart windows, optical filters, and bistable displays. However, it is often difficult to decipher the role of the polymer network architecture on the alignment and the texture of liquid crystals. In this study, we use a simple model system where a small amount of polymerizable liquid crystalline monomer is mixed in a liquid crystal that exhibits both a smectic phase and a cholesteric phase with a large helical pitch. By cross-linking the monomer in the smectic phase, the liquid crystal textures become significantly altered. The existence of a polymer network not only creates resistance to form a helix and therefore hinders the formation of cholesteric fingerprints but also modifies the structure of the cholesteric texture. We investigate the effects of changing the concentration of chiral dopant and monomer on the formation and growth of the cholesteric fingerprint texture during the phase transition and on the width of the fingerprints. We find that, within a certain parameter range, the cholesteric fingerprints do not depend on the concentration of the chiral dopant. We explain this phenomenon by hypothesizing that the polymer network acts as a bulk alignment field.

Computation Legendre moments using image analysis technique

Abstract In this paper, phase transition temperatures of nematic liquid crystals: 4-n alkoxy benzoic acid (nOBA, where n = 4 and 6) are determined from the Legendre moments of liquid crystal textures. Here, the image analysis technique in conjunction with polarizing optical microscope is used to compute the Legendre moments from the textures of liquid crystals. As a function of temperature, Liquid crystal textures are recorded from the arthroscopic mode of optical microscope. Changes in textural features of the sample with respect to temperature bring the variations in intensity values of liquid crystal textures. The brightness image that is generated from the liquid crystal textural patterns separates the information about fluctuations in intensity. In this approach, Legendre moments are computed from the brightness images of the liquid crystal textures and are plotted as a function of temperature. Significant variations in the brightness Legendre moment curve provide insight into the liquid crystal transition temperatures. Results obtained from the present methodology are compared with gray color textures data and the experimental technique of differential scanning calorimetry and are in good agreement with each other. This method is an objective and quantitative technique whereas POM method is qualitative and subjective.

Sub-structures and phase transitions of bi-tilted smectic CG in dimer liquid crystals induced by amide functionalised graphene oxide

ABSTRACT A unique ferroelectric smectic CG phase, in its bi-tilting configurations induced by admixture of the dimeric liquid crystal (LC) 7OBA, serving as an matrix and amide functionalised graphene oxide (AmGO) was presented. Thus, an electrooptically tunable functionalised nanocomposite, indicating bi-tilting state, displayed by two sub-structures, CGcl (clinic) and CGln (leaning) was created. Using both microtextural and DSC analysis, we studied the thermal and structural features of the functionalised nanocomposite. By endothermal peak asymmetry analysis, we found an intermediate between CGcl and CGln state. An enhanced degrees of freedom of the LC director was indicated, allowing an increase of the corresponding micropolarisation LC textures able to create surface memorisation and reach information, respectively.

Effect of varying concentration of dichroic dye on textural, electro-optical, phase transition and band gap studies of zinc oxide nanoparticles induced vertically aligned liquid crystals

Vertically aligned liquid crystal (VALC) perpetually boosts the advancement for display devices and optoelectronics. Herein, initially, the nanoparticles (NPs) induced VALC (nVALC) cell was prepared via doping of 0.3 (wt./wt.%) of zinc oxide NPs in nematic liquid crystal (LC). After that, a series of orange azo dichroic dye doped nVALC cells were prepared with varying concentrations of dye such as 0.0625, 0.125, 0.25 and 0.5 wt.%. The effect of dye concentrations on LC textures, phase transition, electro-optical and band gap properties were investigated, as well as resulted in a significantly reduced value of the threshold and operating voltages as a function of dye concentrations. The contrast ratio was also enhanced up to 0.25 wt.% dye doped nVALC cells. Additionally, the transition temperature from nematic to isotropic phase and band gap studies were also performed. The present work provides improved properties of nVALC systems for next-generation display technologies.

Effect of methyl methacrylate concentrations on surface and thermal analysis of composite polymer polymethylmethacrylates with mesogen reactive RM82

ABSTRACT This research report of the synthesis of composite polymers from liquid crystal mesogen reactive (RM82) monomers with Methyl methacrylate (MMA). The purpose of this research is analysis the effect concentration of MMA on the surface and thermal of the composite polymer PMMA-RM82. The result of the morphological analysis of composite surfaces performed by polarization optical microscopy (POM) technique showed liquid crystal textures affected composition from two monomers. SEM images show that the surface of the RM82 liquid crystal has a shape resembling fibrous and blade-like crystals with a length of up to 10 μm (micrometers). Analysis thermal showed the heat released by the PMMA-RM82 increased with the increase in MMA weight percent. This affects the rapid crystallization process of PMMA-RM82 which of concentration MMA 30%-RM82 the heat released is almost twice as much as the heat released by MMA 5%-RM82. The absence of PMMA and RM82 peaks both endothermic and exothermic in PMMA-RM82 samples indicates that polymerization has occurred and a new product has formed. Analysis structure molecule by FTIR found that the IR spectral form of each variation in the weight percent of MMA was almost the same, but there was a spectral shift that showed that polymerization had occurred in PMMA-RM82 which was characterized by a reaction to the free radical C=C bond released by the photoinitiator. XRD pattern of composite PMMA-RM82 showed the peaks formed are located at scattering angles similar to RM82 but there is a decrease in intensity as the percent weight of MMA increases.

Polyethylene glycol regulates the pitch and liquid crystal behavior of cellulose nanocrystal-based photonic crystals

Inspired by iridescent color in natural creations, cellulose nanocrystal (CNC) photonic crystals artificially created by nanotechnology have great application prospects due to their potential to control light propagation in the linear and nonlinear regimes. One of the most important development directions of photonic crystals is the diversification of colors, usually by adjusting the pitch. However, few researchers notice the effect of polymer molecular weight and content on pitch regulation and the interaction between polymer and CNC liquid crystals. Polyethylene glycol (PEG) were used as polymers to regulate the pitch of CNC photonic crystals and investigate the changes in microstructure, crystal structure, thermal properties, and liquid crystal texture of the composites by changing the PEG content and molecular weight. Different photonic crystal construction systems show that when the molecular weight of PEG is 0.4 k, it can be filled between CNCs to regulate the pitch of photonic crystals, while when the molecular weight of PEG is 20 k, it cannot always be filled between CNCs in evaporation-induced self-assembly (EISA) process due to the depletion interaction, which cannot effectively regulate the pitch. This study reveals the relationship between PEG and CNC liquid crystals, which supports the development of photonic crystals and the pitch regulation.

Phototuning structural color and optical switching cholesteric textures in azobenzene-doped cholesteric liquid crystals

The first integration of structure modulation and phase modulation of CLCs has been accomplished. CLCs doped with azobenzene show rapid color shifts and phase modulation dependent on different intensity light source stimuli within a few seconds.

Detection of glyphosate residues in agricultural products using liquid-crystal-based sensor exploiting competitive binding of glyphosate and Cu2+ at the aqueous/LC interface and capillary tube test strip

Glyphosate is a widely used herbicide that poses both health and environmental risks. In this study, we propose a liquid crystal (LC)-based assay for glyphosate detection that exploits the unique properties of LC materials. The nematic LC 4-cyano-4′-pentylbiphenyl (5CB) was employed as the sensing material and a self-assembled monolayer of octadecyltrichlorosilane (OTS) was used to modify glass substrates. The assay involved strong competition for coordination with Cu2+ for glyphosate, resulting in changes in the LC texture. By monitoring and analyzing the optical images of the LC film using polarizing microscopy, we detected and quantified the glyphosate concentrations. The proposed assay demonstrated high sensitivity and selectivity toward glyphosate in the detection range of 1–300 nM with a limit of detection of 0.26 nM. Moreover, the assay successfully applied to analyze glyphosate in spiked samples, including tap water, soil, and cabbage, and satisfactory recovery rates were achieved. Based on this detection principle, capillary tube test strips were developed for on-site applications. The detection thresholds of the test strips were controlled by varying the Cu2+ concentration. The developed LC-based assay is a rapid and reliable glyphosate detection method with potential applications in environmental monitoring and food safety.

Machine learning studies for liquid crystal texture recognition

ABSTRACT Machine learning techniques such as local binary pattern algorithm and convolutional neural network were applied to study textures of liquid crystal compound (S)-4’-(1-methyloctyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-benzoate (3F7HPhH7). This compound exhibits in its polymorphism several smectic phases (smectic A, ferroelectric smectic C and antiferroelectric smectic C) and two glass states of antiferroelectric smectic C phase, which textures are difficult to distinguish. Proof-of-concept evidence is provided, demonstrating the ability of machine learning algorithms to identify transition temperatures and the respective phases involved. The article describes the procedure for preparing a dataset of textures obtained from polarised microscopy for classification using convolutional neural networks, especially in cases where the image dataset is unbalanced. It utilises the feature of their self-similarity and image augmentation, particularly the cropping procedure. A Kolmogorov–Smirnov test was conducted to check if selected images do not carry the same information.

Liquid crystal textures, neural networks and art

ABSTRACT The ability to create art and advance science are distinguishing features of the human species. Currently, these fields are rarely interconnected. This publication presents liquid crystal textures in terms of their aesthetics. This manuscript covers issues from various fields of science and culture: physics, artificial intelligence, and art. The presented publications focuses on the textures of the following phases: nematic, smectic A, smectic B, smectic C, smectic B, smectic I, smectic F, smectic G, smectic H, ferroelectic smectic C and antiferroelectric smectic C. Images of these textures can serve as inspiration for creating new artwork using neural networks. Neural network algorithms like style transfer and DeepDream modified selected liquid crystal textures. The paper discusses the potential applications of the images obtained this way.

Cholesteric liquid crystalline polysiloxanes containing furan ring with selective reflection – synthesis and properties

ABSTRACT In this paper, first series of liquid crystal polymers (PF) synthesised by hydrosilylation of monomer containing furan group (MA), monomer containing cholesterol group (MB), monomer containing D (+)-camphoric acid group (MC) and monomer containing cyano-group (MD), catalysed by platinum catalyst. Another series of liquid crystal polymers (EF) is synthesised by the Dies-Alder reaction of the former series and cross-linker containing bismaleimide group. The results of Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance(1H NMR) showed the successful preparation of various monomers as well as polymers. The thermal properties of two series were characterised by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). We observed dramatic colour changes and Grand-jean textures of polymers using polarised optical macroscope (POM). The results of POM and selective reflection showed that both series of polymers are cholesteric liquid crystals. In the latter series, crosslinking by Diels-Alder reaction can make the liquid crystal better oriented, which can maintain their wonderful liquid crystal (LC) texture and selective reflection, and at the same time, it has a certain regulation effect on the appearance of cholesteric Grand-jean blue texture. The results of X-ray diffraction (XRD) further proved the two series of polymers are cholesteric liquid crystals.

Non-spherical assemblies of chitin nanocrystals by drop impact assembly

Preparing complex non-spherical assemblies of elongated nanoparticles and exploring their topological conformations is a challenge due to liquid crystals' mobility and elastic distortion. Here, we fabricated a variety of non-spherical liquid crystal assemblies of chitin nanocrystals (ChNCs) in a coagulation bath containing sodium triphosphate (STP) by drop impact assembly method, and the forming mechanism and internal topology were systematically investigated. The collection height, ChNCs concentration, and STP concentration have significant influence on the shape and size of the assembled structures. Long-range ordered structures and long-lived topological textures of the ChNCs liquid crystal can be obtained since a molecular interaction of hydrogen bonding and electrostatic attractions between ChNCs and STP occur during the impact assembly. Rheological and kinetic analysis suggested the shear thinning behavior of the ChNCs liquid crystals and the rapid gelation phenomenon of ChNCs induced by STP. Morphology results showed that the rod-like ChNCs in the non-spherical assemblies were orderly and closely arranged with periodic repetition and layered structure. The non-spherical assemblies of ChNCs liquid crystals can be used as carriers of carbon nanotubes, magnetic Fe3O4 nanoparticles, synthesized polymers, and anticancer drugs for functional composite applications. The drop impact assembly method of ChNCs liquid crystal structure is highly controllable on the composition, morphology, and function, which shows promising applications in energy, environmental-friendly, and bioactive materials.

Bone ECM-inspired biomineralization chitin whisker liquid crystal hydrogels for bone regeneration

As a particular cell niche, natural bone extracellular matrix (ECM) is an organic-inorganic composite material formed by mineralization of liquid crystal (LC) collagen fiber network. However, designing bone repair materials that highly imitate the LC characteristic and composite components of natural bone ECM is a great challenge. Here, we report a novel kind of bone ECM-inspired biomineralization chitin whisker LC hydrogels. First, photocurable chitin whisker LC hydrogels with bone ECM-like chiral nematic LC state and viscoelasticity are created. Next, biomineralization, guided by LC hydrogels, is carried out to truly mimic the mineralization process of natural bone, so as to obtain the organic-inorganic composite materials with bone ECM-like microenvironment. The chitin whisker LC hydrogels exhibit superior biomineralization, protein adsorption and osteogenesis ability, more importantly, LC hydrogel with negatively charged –COOH groups is more conducive to biomineralization and shows more desirable osteogenic activity than that with positively charged –NH2 groups. Notably, compared with the pristine LC hydrogels, the biomineralization LC hydrogels display more favorable osteogenesis ability due to their bone ECM-like LC texture and bone-like hydroxyapatite. This study opens an avenue toward the design of bone ECM-inspired biomineralization chitin whisker LC hydrogels for bone regeneration.

Spontaneous electric-polarization topology in confined ferroelectric nematics

Topological textures have fascinated people in different areas of physics and technologies. However, the observations are limited in magnetic and solid-state ferroelectric systems. Ferroelectric nematic is the first liquid-state ferroelectric that would carry many possibilities of spatially-distributed polarization fields. Contrary to traditional magnetic or crystalline systems, anisotropic liquid crystal interactions can compete with the polarization counterparts, thereby setting a challenge in understating their interplays and the resultant topologies. Here, we discover chiral polarization meron-like structures, which appear during the emergence and growth of quasi-2D ferroelectric nematic domains. The chirality can emerge spontaneously in polar textures and can be additionally biased by introducing chiral dopants. Such micrometre-scale polarization textures are the modified electric variants of the magnetic merons. Both experimental and an extended mean-field modelling reveal that the polarization strength plays a dedicated role in determining polarization topology, providing a guide for exploring diverse polar textures in strongly-polarized liquid crystals.

Classification of liquid crystal textures using convolutional neural networks

ABSTRACTWe investigate the application of convolutional neural networks (CNNs) to the classification of liquid crystal phases from images of their experimental textures. Three CNN classifier model types (Sequential, Inception and ResNet50) are tuned and trained on five individual phase group datasets. The complete dataset includes images of the cholesteric phase, chiral fluid smectic A and C phases and hexatic smectic I and F phases, all extracted from polarised microscopy videos of various liquid crystalline compounds. Three binary classification tasks, each including two liquid crystal phases, provide the foundational demonstration of CNN model viability. The average test set accuracies obtained are approximately (95 ± 2)%. More complex multi-phase datasets are also created and investigated, with a three-phase cholesteric, fluid smectic, and hexatic smectic set, in addition to a set containing all five individual phases. The average test set accuracies for these classification tasks are (85 ± 2)%.

Elastic spectra for a structurally chiral finite slab

We consider an artificial helical solid whose lattice vectors rotate around a given axis when displacing along such an axis; emulating the texture of a cholesteric liquid crystal. We analyze the general case of a local crystal symmetry for which the stiffness parameter values are such that the longitudinal and transverse elastic waves are coupled, causing the system to exhibit simultaneously two types of band gaps. Here, we calculate analytically for the first time, the elastic spectra of a structurally chiral elastic slab whose helical axis is normal to the sample borders, made with a finite number of periods; when elastic longitudinal and transverse circularly polarized waves impinge the slab. The outstanding features of the mentioned bandgaps are the following. One exhibits a circularly discriminatory behavior, in which only the right circularly polarized waves are reflected, whereas the left circularly polarized waves pass practically without change. The other band gap converts longitudinal incident waves in right circularly polarized reflected waves and vice versa.

Functionalized Triphenylene Discotic Molecules: Synthesis and Mesomorphic Characterizations

AbstractWe report the synthesis and characterization of two sets of triphenylene derived discotic molecules with phenol, aldehyde and acid functional groups. In the first set, triphenylene moiety was tethered with benzene derivatives via an ester linkage, while in the second set via an ether linkage with increased aromatic conjugation. All the molecules have triphenylene disc at one end and with benzene, biphenyl and terphenyl cores at the other end connected via flexible methylene spacers. The chemical structures of the novel compounds were confirmed by IR, NMR spectroscopy and CHN analysis methods. Thermal and liquid crystal texture properties were determined using differential scanning calorimetry, polarized optical microscope and X‐ray diffraction studies. Amongst all the novel compounds, only the terphenyl derivative displayed mesomorphism. However, their charge transfer complexes with trinitrofluorenone (TNF) an electron acceptor exhibited columnar mesophases.

A cellulose nanocrystal templating approach to synthesize size-controlled gold nanoparticles with high catalytic activity

Advanced templating methods have shown precise regulation of the micro/nanostructures of inorganic catalysts. Here, on the basis of controlled self-assembly and micro-structures of cellulose nanocrystals (CNCs), a new bio-mass-mediated templating approach is proposed to control the growth of gold nanoparticles (Au NPs). The catalytic performance of the as-prepared Au NPs was evaluated using p-nitrophenol as a model pollutant. TEM, POM, zeta-potential, and rheological measurements were conducted to investigate the structure and catalytic activity of the nano-materials. By regulating the chiral nematic liquid crystal texture formed by the self-assembly of CNCs, the size of Au NPs could be adjusted at the nanoscale dimension, from 1.38 ± 0.38 nm to 4.25 ± 1.24 nm. Depending on the Au size, a high catalytic effect, namely, 98.0% conversion rate, was obtained within 30 min. The conversion rate was maintained at 97.0% even after 3-run cyclic application. Such findings demonstrate the potential of using CNCs as a bio-template to control the growth of nanomaterials.

Magic tetraphenylethene Schiff base derivatives with AIE, liquid crystalline and photochromic properties

Two novel aggregation-induced emission (AIE) active Schiff bases (P4C12 and P5C12) harnessing excited-state intramolecular proton transfer (ESIPT) process derived from tetraphenylethylene and 4-(dodecyloxy)-2-hydroxybenzaldehyde were reported. P4C12 exhibits photochromism in original powder and crystalline states. In contrast, P5C12 exhibits photochromism in original powder, but totally different photochromic and fluorescence properties in its two crystalline polymorphs. The reed leaf crystal (P5C12-A) exhibits very weak fluorescence and reversible photochromic behavior, while the small block crystal (P5C12–B) emits relatively stronger fluorescence without photochromism. Detailed investigations indicate that, different crystal packing styles result in different photoinactivation ways, accounting for different photochemical and photophysical properties. As photochromic molecules, P4C12 and P5C12 show reversible color and fluorescence changes upon UV light irradiation and visible light with good fatigue resistance, which makes them suitable for data storage and anti-counterfeiting materials. Moreover, P4C12 shows anisotropic crystal without liquid crystal texture, while P5C12 shows reversible liquid crystal with smectic phase.

Poly(l-Lactide) Liquid Crystals with Tailor-Made Properties Toward a Specific Nematic Mesophase Texture.

This paper presents the liquid crystal (LC) properties of poly(l-lactide) (PLLA). Mesophase behavior is investigated using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry. The performed analyses confirm that pressed PLLA films exhibit the unique capability of self-assembling into a nematic mesophase under the influence of mechanical pressure, temperature, and time. It was originally demonstrated that the chiral nematic mesophase can be obtained by introducing fine powders into the polymer. Based on the research conducted, it was proved that the pressed PLLA films have a chiral nematic mesophase with a nematic-to-isotropic phase transition and a large mesophase stability range overlapping the temperature of the human body, which can persist for years at ambient temperature. The obtained films show tailor-made properties toward a nematic mesophase with a specific texture, including colored planar texture of the chiral nematic mesophase and blue-phase (BP) LC texture. The BP, described for the first time in plain PLLA, occurred over a wider than usual temperature range of stability between isotropic and chiral nematic thermotropic phases (ΔT ≈ 9 °C), which is an advantage of the obtained polymer material, in addition to ease of preparation. This opens up new prospects for advanced photonic green applications.