Properties Of Liquid Crystals Research Articles

Effect of Confinement on the Structural, Dielectric, and Dynamic Properties of Liquid Crystals in Anopores

Based on data from broadband dielectric spectroscopy (BDS) and a molecular model based on the Landau–de Gennes concept, the effect of confinement on the structural, dielectric, and dynamic properties of 4-n-pentyl-4′-cyanobiphenyl (5CB) in the nematic phase is studied. The dielectric permittivity and relaxation times were previously obtained by the BDS technique in a wide frequency range (1MHz≤f≤1GHz) in the nematic phase composed of 5CB molecules confined to Anopore membranes with pore sizes of 0.2 μm. The distance-dependent values of the order parameter P2(r), the relaxation time τ(r)≡τ001(r), the rotational diffusion coefficient D⊥(r), and both rotational viscosity coefficients γi(r) (i=1,2) as functions of the distance r away from the bounding surface are calculated by a combination of existing statistical-mechanical approaches and data obtained by the BDS technique. Reasonable agreement between the calculated and experimental values of γi(i=1,2) for bulk 5CB is obtained.

Towards greener enantioselective liquid chromatography: An exploratory study on chiral liquid crystals.

Towards greener enantioselective liquid chromatography: An exploratory study on chiral liquid crystals.

Investigation of the effect of doping of newly synthesised bismuth ferrite nanoparticles on the dielectric property of the negative anisotropic nematic liquid crystal

ABSTRACT Bismuth ferrite (BiFeO₃) is an auspicious multiferroic material exhibiting both ferroelectric and ferromagnetic properties, making it attractive for diverse technological applications. In this study, high purity BiFeO₃ nanoparticle nanoparticles were synthesised using a simple and efficient soft chemical route with tartaric acid as a promoter, yielding nanostructures with an average particle size of 16 nm. The nanoparticles demonstrated enhanced ferromagnetic properties within a specific particle size range alongside distinct linear optical characteristics in an isotropic environment. In negative anisotropic environments, such as N-(4-methoxybenzylidene)-4-butylaniline (MBBA) liquid crystals, varying the weight percentage of BiFeO₃ nanoparticles resulted in notable changes in dielectric anisotropy. A peak dielectric anisotropy was observed at a nanoparticle concentration of 0.3%wt. Furthermore, frequency-dependent anisotropy measurements revealed trends consistent with pure liquid crystal samples as nanoparticle concentrations increased. The unique magnetic, optical, and dielectric properties of BiFeO₃ nanoparticles position them as excellent candidates for a broad range of applications, including electronics, spintronics, catalysis, and biomedical technologies.

Cholesteric Behavior of Poly(γ-benzyl-l-glutamate)-Functionalized Nanoparticles.

Following earlier work showing that nanoparticles (NPs) with semiflexible polymer ligands can form lyotropic nematic liquid crystals (LCs), this strategy was expanded to explore whether other LC phases are accessible by using synthetic polypeptides. The key finding of this work was that ZrO2 NPs grafted with poly(hexyl-isocyanate) ligands can exhibit liquid crystalline properties independently, without needing to be dispersed in a LC matrix. Following this result, poly(γ-benzyl-l-glutamate (PBLG) was chosen due to its well-understood cholesteric LC properties. Phosphonic acid-functionalized PBLG ligands of different molecular weights above the threshold to form lyotropic phases were synthesized and grafted to 4 nm metal oxide NPs and assessed for LC behavior. Cholesteric lyotropic phases, gels, and fibrils were observed and characterized by optical microscopy and small-angle X-ray scattering. Pinning of PBLG chains to NPs had the largest effect for low molecular weight PBLG with a significant decrease in the critical concentration required to form a lyotropic phase. This trend diminished as the molecular weight of the PBLG ligands increased. Structure wise, the NP contribution enlarges the cholesteric structure with an increased cholesteric pitch owing to the steric requirements of the tethered PBLG ligands. In general, the PBLG-NPs behave like the free polymer, indicating that NPs with synthetic polypeptide ligands, given their relatively simple synthesis, are promising building blocks to construct biocompatible, stimulus-responsive nanocomposites as well as for NP-based biomedical applications.

Exploring Liquid Crystal Properties through the Two-Phase Thermodynamic Model: Structural, Dynamic, and Thermodynamic Properties.

This work provides a comprehensive analysis of the structural, dynamic, and thermodynamic properties of liquid crystals (LCs) along with their evolution through phase transitions and mesophases. A model of purely repulsive semiflexible spherocylinders is used in a molecular dynamics scheme through simulations involving NPT and NVT combinations. The two-phase thermodynamic model was used to obtain the translational, rotational, and vibrational density of states as well as the absolute values of thermodynamic parameters. We show evidence that during the isotropic-nematic-smectic-solid transitions, the translational diffusion coefficient becomes anisotropic, initially increasing by 15% in the nematic mesophase with a 129% rise along the director vector. Subsequent transitions result in a reduction of the diffusion coefficient by 42% in the smectic phase and 90% in the crystalline phase. Rotational diffusion decreases across all transitions (12, 35, and 26% for nematic, smectic, and solid transitions), although a notable increase in rotation around the principal axis is observed during the last transition. Thermodynamic analysis reveals that the primary contribution to the Gibbs free energy arises from the mechanical term (PV). With regard to the components, rotational motion is the dominant contribution to the Helmholtz free energy in the first transition, while translational motion dominates in the last transition. For the intermediate transition, translational, rotational, and vibrational contributions are comparable. A thorough analysis has been conducted into the Cartesian projections and the principal axes of rotation, in addition to the "solid and gas components" from the two-phase thermodynamic model analysis.

Advanced Optical Encryption Using Tunable Color and Polarization Separation in In-Situ Polymerized Chiral Liquid Crystals.

With the rapid advancement of modern communication technologies, safeguarding information against forgery and unauthorized access has become increasingly critical, driving interest in advanced optical encryption systems. These systems excel in parallel image data processing, enabling swift detection and verification of sensitive information. However, traditional light-based encoding methods are constrained by their limited dependence on static parameters such as light wavelength and intensity and lack dynamic, reversible adaptability. To overcome these limitations, we propose an optical cryptography system that utilizes the tunable color and polarization selectivity of in situ polymerized, multicolor patterned chiral liquid crystals. This system capitalizes on the multifunctional optical properties of chiral liquid crystals, including thermally induced phase transitions that allow reversible and repeatable tuning, rendering encoded information unidentifiable until specific conditions are met. Furthermore, the system incorporates advanced disguising mechanisms through color separation, revealing accurate information only under predefined conditions. Key to its enhanced functionality is the integration of circular polarization selectivity, enabling electrically switchable polarization separation. This feature facilitates the display of distinct information under right- or left-handed circularly polarized light. By exploiting the dynamic optical properties of chiral liquid crystals, our system offers a multilevel encryption platform that significantly enhances data security. This versatile approach surpasses the limitations of conventional methods, providing a robust solution for secure data encoding and anticounterfeiting applications.

Mixed ionic-electronic conductivity in ZnO doped tunable soft materials

Incorporating nanomaterials into liquid crystals has gained popularity since the rise of nanotechnology in the 1990s. The modifications of the physical and chemical properties of liquid crystals are envisioned with the formulation of nanocomposites. In this work, we provide the experimental evidence for the enhancement in the conductivity observed in composites of ZnO nanoparticles (NPs) doped in hydrogen bonded liquid crystals (HBLCs) (P18:FBA) built with (4-pyridyl)-benzylidene-4ʹ-n-octadecylaniline as proton acceptors and 4-Fluorobenzoic acids as proton donors. The FTIR and Photoluminescence studies confirmed the decreased H-bonding interactions proving an efficient pathway for the observed conductivity in the nanocomposites. A theoretical model is proposed for the quantitative explanation of observed conductivity which emphasizes mixed ionic-electronic conductivity.

Synthesis and Optoelectronic Properties of Perylene Diimide-Based Liquid Crystals.

Perylene diimide (PDI), initially synthesized and explored as an organic dye, has since gained significant recognition for its outstanding optical and electronic properties. Early research primarily focused on its vibrant coloration; however, the resolution of solubility challenges has revealed its broader potential. PDIs exhibit exceptional optical characteristics, including strong absorption and high fluorescence quantum yield, along with remarkable electronic properties, such as high electron affinity and superior charge carrier mobility. Furthermore, the robust π-π stacking interactions and liquid crystalline behavior of PDIs facilitate precise their self-assembly into highly ordered structures, positioning them as valuable materials for advanced applications in optoelectronics, photonics, and nanotechnology. This article provides a comprehensive review of the progress made in the design, synthesis, and optoelectronic performance of PDI-based liquid crystals. It explores how various substituents and their placement on the PDI core impact the properties of these liquid crystal molecules and discusses the challenges and opportunities that shape this rapidly evolving class of optical materials. This review is strictly focused on PDIs and does not cover their elongated or laterally extended derivatives, nor does it include monoimide or ester compounds.

Investigation of electro-optical and dielectric properties of polymer dispersed liquid crystal containing WS2 quantum dots and polyfunctional monomers

Investigation of electro-optical and dielectric properties of polymer dispersed liquid crystal containing WS2 quantum dots and polyfunctional monomers

Millimeter-Wave Measurement of Anisotropy Permittivity for Liquid Crystals Based on Open Resonator Method

Abstract The liquid crystal (LC) can be applied in the reconfigurable RF devices due to its excellent tuning capacity of dielectric property. Accurate characterization of its anisotropic permittivity is critical for the optimization of high-frequency or high-speed circuits and components. This work developed a nondestructive quasi-optical Fabry-Perot open resonator and the anisotropic dielectric properties of LC were measured at W band. The dielectric anisotropy of LC was experimentally studied in (75~110) GHz, with the tunability about 22%.

DFT investigation on the effect of asymmetry on electro-optical properties of bent-core liquid crystals

ABSTRACT In this paper, we have studied the effect of asymmetry and bent-core LC phases (B1 & B2) on electro-optical and thermal parameters utilizing the DFT/B3LYP/6-31G** technique on 4-((3-((4-(((4-(decyloxy)phenyl)imino)methyl)benzoyl)oxy)phenoxy)carbonyl)phenyl-4-(alkyloxy)benzoate [DIBCPnB] homologous molecules. Raman spectra of homologous molecules (10a-10g) have been analyzed using the DFT method, while UV-vis spectra are analyzed by both the TD-DFT and ZINDO methods. The effects of asymmetry and phase on electro-optical properties e.g. dipole moment, total energy, anisotropic polarizability, mean polarizability and molar refractivity, as well as global parameters like electronegativity, electron affinity, ionization potential, electrophilicity index, chemical hardness, electron-accepting capability and electron-donating capability have been investigated. The dependence of thermal properties on asymmetry and phases has been examined. This study reveals that asymmetry does not affect total energy, polarizability and molar refractivity. We report that homologues exhibiting the B1 phase possess lower anisotropic polarizabilities than those in the B2 phase.

Liquid crystal properties of cellulose/4-(ω-(methylimidazole)hexyloxy)-4'-(cyano)-biphenyl/amine-modified graphene solution and its high-strength fiber

Liquid crystal properties of cellulose/4-(ω-(methylimidazole)hexyloxy)-4'-(cyano)-biphenyl/amine-modified graphene solution and its high-strength fiber

Nanoparticles in thermotropic and lyotropic liquid crystals

Over the last few decades many applications of liquid crystals have been developed, including the widely employed technology of low-power, flat-panel liquid crystal displays (LCDs), but also sensors, photonic devices and other non-display applications employed in medicine and drug delivery. In recent years, the research trends have shifted in other directions. Nanotechnology and nanoscience have garnered significant attention in liquid crystal research since various nanomaterials or nanoparticles (NPs) can be added directly to the liquid crystalline mesogenic phases. The main idea is to modify the physical properties of liquid crystals or to increase their functionality through the addition of nanomaterials, but also to exploit the self-assembly and spontaneous ordering of LCs into structures or patterns that can be templated by dispersed particles. The neat liquid crystals and the doped nanoparticles/nanomaterials exhibit different behaviours when mixed together. The nanoparticles can influence the alignment and orientation of liquid crystals, and their interaction with the liquid crystals causes the changes in the optical, electrical, and mechanical characteristics of the composite. At the same time the liquid crystal can affect the ordering, structuring and properties of the nanomaterials, for example by transfer of helical order. In this review, we discuss the effects of nanoparticles dispersed in liquid crystals. Several categories of nanomaterials such as metallic, carbon allotropes, nanorod and nanowires will be introduced, together with particles of additional functionality, like ferroelectricity, semiconductors and quantum dots. The combination of liquid crystals and nanoparticles leads to a wide range of applications and novel technologies.

MODELAGEM DE MISTURAS BINÁRIAS PELA APLICAÇÃO DA EQUAÇÃO DE SCHRÖEDER-van LAAR A UM CONJUNTO DE SUBSTÂNCIAS COM DIVERSIDADE ESTRUTURAL

MODELING OF BINARY MIXTURES BY APPLYING THE SCHRÖEDER-van LAAR EQUATION TO A SET OF SUBSTANCES WITH STRUCTURAL DIVERSITY. The Schröeder-van Laar equation to predict the theoretical eutectic melting temperature values was applied to a set of fourteen binary mixtures (UR1 to UR14). The fourteen binary mixtures belong to a structurally diverse group of organic molecules. They are represented by the 5-membered heterocycles containing N-S and N-O rings, flexible methylene chains (RH), semi-rigid semi-fluorinated chains (RF), and hydrogen bonds (HB). A virtual screening totalizing ninety-one possible theoretical combinations was planned. The UR1 to UR14 were prepared by mixing individual components using the calculated mole fractions. The experimental (Te) and theoretical (Tt) temperatures for the eutectic melting points were determined using polarized optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. Heterogeneous mixtures were formed for components with large structural diversity as seen by POM. During the melting of the mixtures, irregular behavior through the segregation of the components was recorded. The study showed that the similarities in structural diversities favor the formation of homogeneous mixtures, with Te values approaching Tt, as predicted by the Schröeder-van Laar equation and by the theory of eutectic mixtures. Liquid crystal properties were affected in homogeneous binary mixtures containing one of the individual liquid crystal components.

Low field electrocaloric effect at isotropic-ferroelectric nematic phase transition.

Electrocaloric effects (ECE) in solid state materials, such as ferroelectric ceramics and ferroelectric polymers, have a great impact in developing cooling systems. Herein, we describe the ECE of a newly synthesized ferroelectric nematic liquid crystal compound at the isotropic-ferroelectric nematic (I-NF) phase transition. While the Joule heat completely suppressed the ECE in a DC field, in an AC field with E < 1.2 V μm-1 and f ≥ 40 Hz, an increase in optical transmittance was observed, which in comparison with a zero-field transmittance versus temperature plot indicated a shift in the transition temperature. These findings implied that one can induce the desired phase transition using an electric field via ECE with an EC responsivity of ∼1.7 × 10-6 km V-1. Notably, the required electric field was two orders of magnitude smaller than the typical fields for other EC materials. EC effects observed under such low fields is a unique property of ferroelectric nematic liquid crystals. Furthermore, the specific EC energy could be increased considerably by reducing the ionic content, thus suppressing the Joule heat.

Tuning liquid crystal properties with 0D carbon dots: exploring the impact of functionalization of carbon dots

CD decreases conductivity whereas ODACD increases conductivity of the NLC matrix. CD increases elastic constant ratio better as compared to ODACD in NLC.

Features of magnetically induced exceptional points in cholesteric liquid crystals

Abstract In this work, the photonic properties of cholesteric liquid crystals (CLCs) in an external magnetic field parallel to the helix axis are investigated for the first time in the short-wavelength band of the spectrum, where exceptional points (EPs) are found. It was shown that at EP the real parts of two of four wave numbers touch each over, and their imaginary parts intersect. Here the reflection, transmission and absorption show the same values for two eigenmodes of CLC layer. At anisotropic absorption near the EP there appear points where the magnetically induced transmittance and absorption are observed. The light localization peculiarities as well as photonic density of states (PDOS) peculiarities near these points were also investigated. Near EPs, PDOS for two eigenmodes shows significant changes, especially with different magneto-optical activity parameters.

Moving Mesh Partial Differential Equation Modelling of a 5CB Nematic Liquid Crystal Confined in Symmetric and Asymmetric Pi-Cells: A Review

The switching properties of nematic liquid crystals under electrical and mechanical stresses play a fundamental role in the design and fabrication of electro-optical devices. Depending on the stress applied to a nematic texture confined in a pi-cell, different nematic configurations are allowed inside the cell, while the induced distortion is relaxed by means of growing biaxial domains which can end with the order reconstruction phenomenon, a transition connecting two topologically different nematic textures which can occur in different regions of the pi-cell. Due to the different space and time scales involved, modelling in the frame of the Landau–de Gennes order tensor theory is mandatory to correctly describe the fast-switching mechanisms involved, while from a computational point of view, sophisticated numerical techniques are required to grasp tiny and fast features which can be predicted by the mathematical modelling. In this paper, we review the results obtained from the mathematical and numerical modelling of a 5CB liquid crystal confined in a pi-cell performed by using a numerical technique based on the equidistribution principle, tailored for the description of a complex physical system in which fast switching phenomena are coupled with strong distortions. After a recap on the underneath theory and on the numerical method, we focus on the switching properties of the nematic material when subjected to variable mechanical and electrical stresses in both symmetric and asymmetric conditions.

Circularly Polarized Luminescence in Cellulose-Based Assemblies: Synthesis, Regulation, and Application.

Currently, circularly polarized luminescence (CPL) has drawn wide interest in 3D display, information storage, and optical sensing. However, traditional synthetic paths are often accompanied by low chiral optical intensity and complex processes. Cellulose nanocrystals (CNCs), with the properties of liquid crystals, can spontaneously arrange into the left-handed layered nanofilm, which enables them candidates in the construction of CPL materials. Following this approach, this work reviews the synthesis of cellulose-based chiral luminescent materials. The co-assembly technique, in situ intercalation strategy, and defect destruction design are efficient in encapsulating the luminophores into the CNC organization. Next, various strategies on the CPL regulation, including the matching of the photonic bandgap, optical pathway design, and tailored helical structure, are summarized. These offer new sights in the CPL control, mainly focusing on the amplification and inversion of optical signals. Multimodal and convertible chiroptical signals enable the photonic films with practical values in anti-counterfeit, sensing, and handedness induction. Overall, this timely overview summarizes the synthesis, regulation, and application of cellulose-based CPL materials, and aims to inspire the development of the chiral optical materials.

Design of Chemoresponsive Liquid Crystals Using Metal-Coordinating Polymer Surfaces.

Liquid crystals (LCs), when interfaced with chemically functionalized surfaces, can amplify a range of chemical and physical transformations into optical outputs. While metal cation-binding sites on surfaces have been shown to provide a basis for the design of chemoresponsive LCs, the cations have been found to dissociate from the surfaces and dissolve slowly into LCs, resulting in time-dependent changes in the properties of LC-solid interfaces (which impacts the reliability of devices incorporating such surfaces). Here, we explore the use of surfaces comprising metal-coordinating polymers to minimize the dissolution of metal cations into LCs and characterize the impact of the interfacial environment created by the coordinating polymer on the ordering and time-dependent properties of LCs. In particular, by combining theoretical (electronic structure calculations) and experimental (polarization-modulation infrared reflection-adsorption spectroscopy) results, we determine that the pyridine groups of a thin film of poly(4-vinylpyridine-co-divinylbenzene) (P(4VP-co-DVB)) coordinate with Ni2+ when Ni(ClO4)2 is deposited onto the film. We provide evidence that the Ni2+-pyridine coordination weakens the binding of Ni2+ with 4'-n-pentyl-4-biphenylcarbonitrile (5CB), a room-temperature nematic LC, as compared to Ni(ClO4)2 supported on glass, although binding is still sufficiently strong to induce a homeotropic (perpendicular) orientation of the LC. Exposure of the 5CB films supported on Ni(ClO4)2-decorated P(4VP-co-DVB) substrates to parts-per-million vapor concentrations of dimethylmethylphosphonate (DMMP) was found to trigger orientational transitions (to planar (parallel) orientations) in the LC films. In contrast, 5CB supported on Ni(ClO4)2-decorated glass surfaces exhibited no response, even though displacement of 5CB by DMMP is predicted by computations to be thermodynamically favored in both cases. We propose that the distinct LC responses measured on glass and the coordinating polymer substrates are governed by the kinetics of displacement of 5CB by DMMP, a proposal that is supported by measurements performed with increasing temperature. Importantly, by using Ni2+ supported on P(4VP-co-DVB), we measured the ordering of 5CB to be stable and long-lived (>7 days), in contrast to unstable LC ordering (<14 h) when using Ni2+ supported on glass under dry conditions and at room temperature. We further demonstrate the stability of Ni(ClO4)2 supported on P(4VP-co-DVB) toward higher temperatures and humidity using E7 as the LC. Overall, these results demonstrate that metal-coordinating polymer films are a promising class of substrates for fabricating robust and long-lived chemoresponsive LCs.