Properties Of Liquid Crystals Research Articles

Biphenyls embedded Schiff base-bis esters: self-assembling behaviour, impact of additional aromatic ring and ester linkage and their DFT investigations

ABSTRACT In the present investigation, two series of biphenyl embedded Schiff base-bis esters alkyl-(E)-4-(((4’-(decyloxy)-[1,1’-biphenyl]-4-yl)methylene)amino)-benzoate, BPK-(2–18) and alkyl-(E)-4-(((4’-((4-(decyloxy)benzoyl)oxy)-[1,1’-biphenyl]-4-yl)-methylene)amino)benzoate, BPEK-(8–18) containing either terminal alkoxy biphenyl core or central biphenyl core have been synthesised and studied for their self-assembling behaviour. The compounds of both series demonstrated enantiotropic liquid crystal properties, displaying typical calamitic mesophases (Smectic A (SmA), Smectic C (SmC)) across a broad temperature range and with high thermal stability. The bimorphic behaviour of new molecules has been investigated by VT-XRD analysis. The density function theory has been done to illustrate the experimental results of the mesomorphic properties of the studied compounds. Several parameters have been calculated such as molecular geometry, dipole moment, polarisability, aspect ratio, etc. The results showed that more planar compounds will attain more packed structures leading to the formation of more ordered smectic phases.

Effect of High-Index Nanoparticles on the Emission Properties of a Dye-Doped Blue Phase Liquid Crystal

Effect of High-Index Nanoparticles on the Emission Properties of a Dye-Doped Blue Phase Liquid Crystal

Exploring the electro-optical properties of nematic liquid crystal through incorporation of ZnCuGaS2 core/shell quantum dots

ABSTRACT The current study focuses on elucidating the interaction mechanisms between ZnCuGaS2 quantum dots (QDs) and nematic liquid crystals (NLCs) (5CB), intending to comprehend how this interaction leads to the alteration of electro-optical properties of the host material. Various concentrations of QDs were incorporated into NLCs and investigated to examine their emission and transmittance characteristics. Remarkably, an enhancement (~68%) in photoluminescence was observed for the concentration of 0.04 wt. %, adding an intriguing aspect to the findings. A notable decrease in the threshold voltage, from 1.5 V (in pure NLC) to 0.5 V, was observed for the optimised concentration (0.04 wt. %) calculated using transmittance-voltage measurement. This sample exhibited a noteworthy improvement in optical transmission, showing an increase by 2.7 times compared to pure NLC. Fundamentally, the introduction of QDs leads to a reduction in light leakage centres and ionic impurities, consequently enhancing radiative recombination. Moreover, the memory effect of the sample was evident in the capacitance-voltage data, revealing that the NLC with QDs significantly increased the capacitance value from 290 pF to 466 pF when compared to the pure NLC. The objective of the present research is to examine the impact of QDs on NLC concerning key parameters such as mentioned above.

Analysing the Photo-Physical Properties of Liquid Crystals

Intrinsically fluorescent liquid crystals are highly sought after for a variety of applications. Most of the measurements of photo-physical properties of liquid crystals are made in dilute solutions, which is mainly due to the relative ease of both these measurements and the interpretation of data. The fluorescence spectra depend on a number of parameters including the concentration in liquid crystal solutions, the device geometry, and the mesophase in which the spectra have been measured. Working with neat, or concentrated, liquid crystal samples adds experimental complexities such as the inner filter effect (IFE), which affects the collection of data, interpretation of the results, and accuracy of the conclusions. In this paper, we present a systematic study of the photo-physical properties of both a model reference material, Nile red, and a nematic liquid crystal, 4-cyano-4′-pentylbiphenyl (5CB). The influence on the emission spectra of an increasing solute concentration is investigated and discussed. Moreover, a detailed investigation of the influence of the used device geometry, as well as the choice of appropriate data fitting methodologies, are presented.

Varifocal occlusion in an optical see-through near-eye display with a single phase-only liquid crystal on silicon

We propose a near-eye display optics system that supports three-dimensional mutual occlusion. By exploiting the polarization-control properties of a phase-only liquid crystal on silicon (LCoS), we achieve real see-through scene masking as well as virtual digital scene imaging using a single LCoS. Dynamic depth control of the real scene mask and virtual digital image is also achieved by using a focus tunable lens (FTL) pair of opposite curvatures. The proposed configuration using a single LCoS and opposite curvature FTL pair enables the self-alignment of the mask and image at an arbitrary depth without distorting the see-through view of the real scene. We verified the feasibility of the proposed optics using two optical benchtop setups: one with two off-the-shelf FTLs for continuous depth control, and the other with a single Pancharatnam–Berry phase-type FTL for the improved form factor.

Construction and Properties of O/W Liquid Crystal Nanoemulsion.

Liquid crystal emulsion is a new type of emulsion, in which the emulsifier molecules are located at the oil/water (O/W) interface and form a long-range ordered and short-range disordered lamellar liquid crystal. The lamellar liquid crystal formed by the emulsifier is similar to the skin stratum corneum lipid structure, which enables it to have a broad application prospect in the fields of cosmetics, pharmaceuticals, etc. In this work, a liquid crystal nanoemulsion was obtained by passing a liquid crystal emulsion stabilized by hydrogenated lecithin and phytosterol combination through a microfluidizer. The microstructure of the prepared liquid crystal nanoemulsion was investigated experimentally by dynamic light scattering, transmission electron microscopy, and small-angle X-ray scattering. The results have shown that the nanoemulsion inherited the liquid crystal emulsion property, namely, the long-range ordered and short-range disordered lamellar structure still existed at the oil/water interface even though they underwent extrusion, friction, and acceleration. At the same time, the underlying mechanisms of the existence of lamellar liquid crystal between the oil phase and the water phase for the nanoemulsion were explored theoretically by molecular dynamics simulations. The simulation results elucidated that the hydrogenated lecithin and phytosterol combination improved the flexibility of the bilayer structure composed of emulsifiers. The bilayers were the basic structure units of lamellar liquid crystals, and thus, the improved flexibility of bilayers provided insurance for the existence of lamellar liquid crystals with larger curvature around the oil droplets. In addition, the applicable properties of liquid crystal nanoemulsion were studied, and the results have shown that the liquid crystal nanoemulsion presented better slow-release and moisturizing properties than traditional nanoemulsions due to the existence of multilayers between oil and water phases. This work not only provides necessary information for the development and effective application of liquid crystal emulsions but also is helpful for in-depth understanding the inner properties of lamellar liquid crystal at molecular level.

Investigation of thermodynamical, electro-optical and dielectric properties of nematic liquid crystals dispersed with low-concentration barium titanate nanoparticles

ABSTRACT A liquid crystals nanoparticles composite was prepared by dispersing barium titanate nanoparticles (BT-NPs) into a multi-component liquid crystalline material having wide range room temperature nematic phase. The thermodynamic, optical textures, electro-optical and dielectric properties of the composite sample were studied along with pristine materials. Isotropic to nematic phase transition temperature was enhanced for nano-composites as observed from thermodynamic, optical textures and dielectric investigations. Effect of BT-NPs dispersion on various display parameters of nematic liquid crystals, namely, threshold voltage, dielectric anisotropy, DC conductivity and splay elastic constant has been explored. A relaxation mode in kHz frequency range has been observed for pure and nano-composites samples, which varies with temperature and follows Arrhenius behaviour. DC conductivity enhances approximately fivefold for BT-NPs dispersed samples. The host liquid crystalline material has nematic ordering which supports alignment of BT-NPs parallel to the nematic director which consequently improves thermal stability, dielectric and electro-optical parameters of the nano-composite system.

Smart emulsion system driven by light‐triggered ionic liquid molecules and its application in eco‐friendly water‐saving dyeing

AbstractThe smart emulsification and demulsification system with the light response is a useful tool in various industries, including green chemistry, catalytic reaction, pharmaceuticals, and environmental remediation. Herein, an ionic liquid crystal compound with a light triggered switch based on the azobenzene group [(4‐{3‐methyl‐1‐[3‐(8‐octyloxyoctyl)oxy‐4‐oxobutanoyl]imidazo‐lium‐1‐yl}octyl)oxy] ‐N‐(4‐methylphenyl)benzene‐1,2‐diazene bromide (MOIAzo), was designed and synthesized, which could cause reversible transition between emulsification and demulsification through the light trigger. The ionic liquid has an efficient photoinduced liquefaction process, which dramatically lowers the melting point of ionic liquids from 79 to 9.2 oC. This significantly broadens the liquid state temperature of the ionic liquid crystal. The ionic liquid crystal MOIAzo exhibits both photoinduced and thermally induced nematic liquid crystal properties. The smart emulsion system was effectively employed in an eco‐friendly water‐saving dyeing process of cationic dyes for cationic dyeable polyester (CDP) fabrics, which used only half the amount of water compared with the conventional water bath dyeing method. After dyeing, the oil and water phases can be efficiently separated through the light irradiation, and the oil phase can be reused for the subsequent dyeing process. This novel smart emulsion dyeing method greatly reduces the water consumption and wastewater discharge. MOIAzo as a light‐triggered ionic liquid molecule opens up new dimensions in green chemistry.

Programmable Liquid Crystal Defects and Dynamically Manipulation with Mechanical Stress

AbstractManual intervention in the self‐assembly of soft matter to obtain a desired defect structure is a complex but significant project. Specifically, the flow and optical properties of liquid crystal (LC) materials have become the most important platform for studying topological structures in ordered physical systems. The regulation of liquid crystals (LCs) is largely limited to established means such as temperature, electric field, magnetic field, etc., however, a new effective strategy by mechanical stress is desirable but elusive. Here, using disclination controlled by stress, topologically continuous superstructure is generated to apply to touch display and wideband vector beam generator. This work demonstrates a new approach for direct controllable manipulation of disclination, unlocking the long‐sought full potential of topological defect, thus paving the way for optical and dynamic applications.

Dielectric anisotropy changes in MBBA liquid crystal doped with barium titanate by a new method

In response to the burgeoning interest in enhancing the properties of liquid crystal composites, this research systematically explores the intricate interplay between MBBA nematic liquid crystals and ferroelectric barium titanate nanoparticles. The focus is modulating dielectric properties under temperature, frequency, and an applied electric field. Nuanced insights into temperature-dependent behavior, parallel and perpendicular component alterations, and a nonlinear correlation between nanoparticle concentration and dielectric constant are revealed. The study delves into dielectric anisotropy, indicating a reduction with increasing temperature. Structural analyses validate size reduction and crystal phase maintenance of barium titanate nanoparticles (NPs), emphasizing their impact on dielectric characteristics. Frequency-dependent investigations underscore a consistent decline in permittivity with rising frequency across nanoparticle concentrations. Application of an electric field in filling process of liquid crystal cells reveals irregular changes in dielectric constant, holding promise for tailored applications in display technologies. These comprehensive findings offer valuable insights into manipulating dielectric anisotropy properties of MBBA liquid crystal by a simple method for potential advancements in optoelectronic devices and display technologies.

Size-dependent optical and dielectric anisotropy of CdS nanowire doped high-birefringent nematic liquid crystalline compound

Highly birefringent liquid crystals have grabbed ample attention because of their potential applications as an active medium for devices in visible, infrared and other spectral regions. Here, we have attempted to study the effect of the size and concentration of CdS nanowires on a nematic liquid crystal. Anisotropy in liquid crystals is one of those distinguishing traits that gain their superiority over other materials. We hereby have analyzed how optical and dielectric anisotropy respond to variations in the size and concentration of the dopant. The study is of significant scientific value because there is very little literature available on how dopant size can alter liquid crystalline properties and also introduces a method to tune the properties of pure liquid crystals (LCs) by varying the size and concentration of the dopant. The study explains how the size of the nanowires changes the analyzed parameters and up to what extent. The obtained results yield a significant increase in both optical and dielectric anisotropy by doping CdS nanowires making them an excellent choice for dopant selection. CdS-doped nematic LC mixtures have proved to be highly birefringent and possess a high positive dielectric anisotropy as well. Such a compound can be of great application in device fabrications such as laser beam steerers, electronic lenses, attenuators and light shutters, etc.

Effect of Laterally Substituted Methoxy Group on the Liquid Crystalline Behavior of Novel Ester Molecules

Background: The aim of this research is to study the effect of length-to-width ratio on mesomorphism to enhance the understanding of its potential applications. This will be achieved by synthesizing a unique and innovative series of identical ester molecules, including lateral methoxy groups and terminal ethyl benzoate groups. In this research, we aim to find new insights into the relationship between molecular structures and mesomorphic behaviors, which could have significant implications for the development of advanced materials with adapted properties. : The objective of the study is to investigate the mesophase behavior of new ester mesogens and determine how they are influenced by lateral methoxy groups. By identifying the underlying perspectives and relationships between these variables, we hope to better understand the unique properties and potential applications of these materials. Method: In this research work, the focus is on the synthesis of ethyl(E)-4-((3-(4-alkoxy-3- methoxyphenyl)acryloyl)oxy)benzoate, which is prepared from Steglich esterification method by using (E)-3-(4-alkoxy-3-methoxyphenyl)acrylic acid and ethyl 4- hydroxybenzoate. Synthesis processes involve precise reaction sequences designed to ensure maximum yield and purity of the final product. By providing a detailed report on the experimental process, this study contributes to the ongoing research efforts aimed at the development of innovative compounds with various applications in liquid crystals Result: A new set of liquid crystal derivatives has been synthesized and studied to investigate the effect of molecular structure on the behavior of liquid crystals, with particular attention to the group -OCH3 located laterally. This series was composed of 12 derivatives (C1-C16). Among them, the first six derivatives (C1-C6) did not have the characteristics of a liquid crystal, while the remaining derivatives (C7 and C8) had a monotropic behavior, and C10-C16 had an enantiotropic smectogenic liquid crystal behavior without exhibition of the nematic phase. The average thermal stability of the smectic property was 87.33 °C, and the mesophase range was 2 °C to 14 °C. The molecular structure was confirmed by analytical and spectral analysis. The properties of liquid crystals of this new series were compared with those of other known structurally similar homologous series. The transition temperatures were determined with an optical polarizing microscope equipped with a heating phase. Conclusion: The mesomorphic thermal and optical properties of the compounds have been validated by DSC and POM techniques. The result shows that the length of the alkyl chain has a significant influence on the mesomorphic characteristics and thermal stability of the different mesophases. Evaluation of the compounds studied indicates that the molecules are sensitive to their lateral substituent, which influences the thermal characteristics and stability of the mesophase.

Ionic strength and phase systems influence nanotubular material functionality

We synthesized novel thiacyanine chromonic liquid crystals (CLCs) and structurally characterized using NMR and mass spectrometry. The impact of distinct substitution at the para position of aromatic counter anions, aliphatic counter ion chain length, and varied spacer parity of thiacyanine dyes on CLC formation is investigated. Liquid crystal properties of the synthesized dyes are characterized by polarizing optical microscopy (POM) and X-ray diffraction (XRD) studies. Dyes exhibit nematic (N), lamellar (Lα), columnar rectangular (Colr), and columnar oblique (Colob) CLCs at different concentrations in the water. Electronic absorption spectra reveal Scheibe aggregation in all the dyes. Cylicvoltametry studies confirm redox behaviour in TC-1a and TC-5e dyes. Chromonic LCs hybrid nano-materials are synthesized using sol–gel method. Scanning electron microscopy employed to confirm nano tubular fiber structure of the hybrid nanomaterilals..

Exploring the multi-state photoluminescence of a thermally stable and liquid crystalline organic molecule

The ability of materials to exhibit efficient fluorescence in both solution and aggregated states opens up new possibilities for their application in areas where both solution-based and solid-state emissions are essential. In this study, we developed a luminescent molecule and conducted investigations into its thermal stability, liquid crystal properties, absorption, and emission behavior. The studied material possesses a simple molecular structure and demonstrates high thermal stability and liquid crystallinity. It also exhibits high emission quantum yield in various states, including crystals, liquid crystals, and liquids, while maintaining stable emission even at high temperatures. The molecule also emitted blue linearly polarized light. This unique combination of features can be attributed to factors such as the rigidity of the molecular structure, the intermolecular interactions of the fluorophore, and the presence of specific functional groups that enhance both thermal stability and emission behavior. The molecule's unique properties have significant potential for various applications in optoelectronics, sensors, displays, and photonics, with a particular emphasis on organic light-emitting diodes (OLEDs) and photovoltaics.

The influence of the side-arms structure on the properties of the liquid crystal dimers centred on mandelic acid

ABSTRACT With mandelic acid (MA) as the chiral core, two series of non-symmetric liquid crystal (LC) dimers have been synthesised by changing the rigidity of the side-arms, namely the DBM-nC2B series and the DBBM-nC2B series. In the DBM-nC2B series, one side-arm is the same, while the length of the flexible tail of the other side-arm increases from 0 to 4. The same is true of the DBBM-nC2B series. Chemical structures and LC properties of the two series LC dimers were characterised by FT-IR, 1H NMR, 13C NMR, DSC, TGA and POM. The results show that the DBM-nC2B series LC dimers display the nematic phase (N), and the DBBM-nC2B series LC dimers exhibit the chiral nematic phase (N*). It shows that the side-arm should have sufficient rigidity for MA to induce the N* phase. In the same series, when the length of the flexible tails of the side-arm increases from 0 to 4, it does not change the mesophase, while it has some effect on the melting temperature (Tm), the clearing temperature (TN(*)I), and mesophase range of the dimers. The molecular length-width ratio (l/w) and dipole moment (μ) were used to explain the variation of Tm and (TN(*)I) of LC dimer.

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

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

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

Ultrasensitive Detection of Lipid-Induced Misfolding of the Prion Protein at the Aqueous-Liquid Crystal Interface.

The misfolding of the α-helical cellular prion protein into a self-propagating β-rich aggregated form is a key pathogenic event in fatal and transmissible neurodegenerative diseases collectively known as prion diseases. Herein, we utilize the interfacial properties of liquid crystals (LCs) to monitor the lipid-membrane-induced conformational switching of prion protein (PrP) into β-rich amyloid fibrils. The lipid-induced conformational switching resulting in aggregation occurs at the nanomolar protein concentration and is primarily mediated by electrostatic interactions between PrP and lipid headgroups. Our LC-based methodology offers a potent and sensitive tool to detect and delineate molecular mechanisms of PrP misfolding mediated by lipid-protein interactions at the aqueous interface under physiological conditions.

Impact of Co-doped TiO2 nanoparticles on the physical properties of a nematic liquid crystal

ABSTRACT We have studied the electro-optical properties of the 4-pentyl-4-biphenylcarbonitrile nematic liquid crystal also known as 5CB doped by 0.5%wt of pure and cobalt-incorporated TiO2 nanoparticles. The obtained results show that the effect of the NPs on the electrooptical properties is mainly due to the modification of the dielectric and the viscoelastic properties of the nematic in the presence of the NPs. Furthermore, the nematic isotropic transition temperature of all doped samples remained almost unchanged. This indicates that the order parameter was almost unchanged too. A significant decrease in the dielectric anisotropy and the splay elastic constant was observed. The rotational viscosity has been deduced from response time data; it was found that rotational viscosity shows a significant increase for cobalt-incorporated TiO2. However, the rotational viscosity was decreased for pure TiO2 nanoparticles compared to pure 5CB.

Liquid crystallinity and magnetorheological performance of polymeric liquid crystal magnetic composites

ABSTRACT Magnetorheological fluids (MRF) are regarded as a novel ‘intelligent’ material because they show the ability to respond to external stimuli. However, with the extension of working time, the agglomeration and sedimentation of magnetic particles become a serious problem, which has a great impact on the magnetorheological performance. Many methods have been proposed to overcome the particle settling problem, including magnetic particle modification and carrier liquid modification, but they all show negative effects on the magnetorheological performance of MRF. A new method to prepare the magnetic liquid crystal (LC) composites [PEA-COOH]SO3H@Fe3O4 series, with Fe3O4 nanoparticles as core and side-chain supramolecular LC polymers with different mesogen contents as coating, were reported. The chemical structure, magnetic property and LC properties were investigated by a variety of techniques. In order to study the effects of the mesogen content and LC phase state of magnetic LC composites on magnetorheological performance and sedimentation stability, MRF based on silicone oil carrier liquid and [PEA-COOH]SO3H@Fe3O4 dispersed phase were prepared. It was found that dynamic yield stress, plastic viscosity and the sedimentation ratio increased slightly with increasing mesogen content in the magnetic LC composites. What’s more, MRF prepared by magnetic LC composites annealed in LC state exhibited better magnetorheological performance and sedimentation stability than those in glassy state and isotropic state. These results indicated that the synergetic effects of LC orientation and magnetic field-induced arrangement of Fe3O4 magnetic particles can improve the magnetorheological performance and sedimentation stability of MRF.