Properties Of Liquid Crystals Research Articles

Spectroscopy, electrochemistry and liquid crystal properties of monosubstituted ferrocene based azobenzene derivatives with 1,2,3-triazole heterocycle

Monosubstituted ferrocene based azobenzene liquid crystals were synthesized, in which ferrocene was flexibly attached to the mesomorphic core by click reaction. The counterpart compounds without ferrocene unit were also prepared. Two series of compounds displayed liquid crystal behaviours during heating and cooling, and had wide mesophase range. In the process of cooling, the compounds underwent a transformation from nematic phase to smectic C phase. When ferrocene was introduced into the molecule, the melting point of most compounds decreased by 30–40 °C, and the mesophase range was still as wide as 71–97 °C. These compounds emitted fluorescence at 400–550 nm and had strong absorption near 280 nm and 350 nm. Under the irradiation of 365 nm ultraviolet light, these compounds transformed rapidly from E to Z isomers, while the reverse reaction occurred slowly in the dark, especially the molecules containing ferrocene. Cyclic voltammetry studies showed that ferrocene based azobenzene derivatives exhibited one electron transfer processes with low formal redox potentials, indicating that these compounds are easily oxidized.

Synthesis and mesomorphic properties of swallow-tailed liquid crystal monomers and polymers

In this article, we designed and synthesized two novel swallow-tailed liquid crystal monomers (M1 and M2) with different chain lengths and rigidities centered on 3,4,5-trihydroxybenzoic acid and two series of side-chain liquid crystals polymers PN1 and PN2. All liquid crystal monomers and polymers were conformed to the molecular designs by FT-IR and NMR. The liquid crystal properties were tested by DSC and POM, and the results showed that M1 and M2 were thermotropic enantiotropic nematic liquid crystals and the side-chain liquid crystal polymers PN1 and PN2 series were typical amorphous liquid crystal polymers. With the increase of monomer content, the glass transition temperatures and clearing points of PN1 and PN2 series enhanced. With the increase of the number of mesogens in the liquid crystal monomer, the rigidity was enhanced, and the liquid crystal performance of the polymer was better.

A Review on Physical, Chemical and Optical Properties of Liquid Crystal

The foundation of the upcoming generation of cutting-edge gadgets and digitally augmented technologies is expected to be smart soft materials. Because of their responsiveness and adaptability, liquid crystals (LCs) are promising smart soft materials. In the 20th century, LCs were crucial to changing the information display sector. However, several beyond-display uses for LCs have been proven at the turn of the twentieth century, neatly using their controlled stimuli-responsive and adaptable properties. New LC materials have been developed and engineered for such applications. The review comes close with a summary and viewpoints on the potential and problems facing LCs as smart soft materials. This review is expected to inspire a wide range of concepts for the application of nature's delicate phase of matter in the generation and beyond of smart and augmented devices.

Effect of shape of ZnO nanoparticle on electro-optic and dielectric properties of nematic liquid crystal

Properties of liquid crystal incorporated with various shapes of a nanomaterial are expected to show multifaceted behaviour as properties of nanomaterial are extremely dependent on its size and shape. In view of this, we have investigated the effect of shape of ZnO nanoparticle on electro-optic and dielectric properties of nematic liquid crystal (NLC), PCH5. Nanocomposites of 0.01 wt% ZnO nano- sphere, rods, and wires in NLC are prepared. The addition of ZnO nanoparticles to NLC leads to increase in the order parameter and reduction in threshold voltage, response time as well as ionic conductivity as compared to the pure NLC host. Dielectric permittivity measurements indicate nanoparticle induces short range order in isotropic phase. Dielectric measurements also show increase in order parameter in nanocomposites with 1D nanoparticles whereas negligible change is observed in nanocomposites with spherical nanoparticles in NLC in deep nematic range. The ATR-FTIR measurements support the enhancement in parallel correlation of dipole moments in ZnO nanocomposites as compared to pure NLC.

Interplay of reorientational and thermal solitons: unveiling the dynamic coexistence and enhanced nonlinear response in nematic liquid crystals

Spatial solitons in nematic liquid crystals (NLC) are optical beams that maintain their transverse profile due to the self-focusing effect of light. The mechanism leading to the formation of solitons can be either light-induced reorientation of the elongated molecules or thermal changes in the refractive index induced by a light beam. The specific optical properties of nematic liquid crystals cause the reorientational and thermal solitons to coexist in NLC, and their mutual competition can lead to a reduction or enhancement of the overall nonlinear response of the NLC. The study of the interplay between reorientational and thermal solitons allows a better understanding of the conditions under which the solitons can coexist, compete, or enhance each other. Here, we show that the simultaneous existence of both soliton types can lead to a more robust and versatile nonlinear response and can be used in competitive and synergistic configurations by carefully controlling the temperature, intensity, and polarization of the propagating light. As a result of our experimental findings, it may be possible to shape the nature of the interplay between reorientational and thermal solitons and better understand the behavior of reorientational solitons under varying thermal conditions. Furthermore, understanding this mutual interplay may provide insights into the potential of advanced NLC-based photonic devices that exploit the joint effect of reorientational and thermal nonlinearities.

Programmable Complex Shape Changing of Polysiloxane Main-Chain Liquid Crystalline Elastomers.

Liquid crystal elastomers (LCEs) are shape-morphing materials whose large and reversible shape transformations are caused by the coupling between the mobile anisotropic properties of liquid crystal (LC) units and the rubber elastic of polymer networks. Their shape-changing behaviors under certain stimuli are largely directed by the LC orientation; therefore, various strategies have been developed to spatially modulate the LC alignments. However, most of these methods are limited as they require complex fabrication technologies or have intrinsic limitations in applicability. To address this issue, programmable complex shape changes in some LCE types, such as polysiloxane side-chain LCEs, thiol-acrylate main-chain LCEs, etc., were achieved by using a mechanical alignment programming process coupled with two-step crosslinking. Here, we report a polysiloxane main-chain LCE with programmable 2- and 3D shape-changing abilities that were created by mechanically programming the polydomain LCE with two crosslinking steps. The resulting LCEs exhibited a reversible thermal-induced shape transformation between the initial and programmed shapes due to the two-way memory between the first and second network structures. Our findings expand on the applications of LCE materials in actuators, soft robotics, and smart structures where arbitrary and easily programmed shape morphing is needed.

Metallomesogens as potential materials for improvement of electro-optical properties of commercial liquid crystals

We present a new approach to utilize the eutectic metallomesogen (MOM) mixtures to improve the electro-optical properties of commercial nematic liquid crystal (NLC) materials. Accordingly, we studied the phase diagrams of rod-like MOM models structures, including alkyl/alkoxy-azobenzene with Pd complex and salicylal-diaminates with Cu, Ni and Pd complexes. These phase diagrams we utilized the eutectic MOM mixtures and mixed them with few commercial NLC hosts. The results showed a complete mesogenic miscibility and wide mesogenic range. Although the studied MOM model materials are not the optimum structures and we did not study the electro-optical properties of MOM-NLC mixtures, the present results indicate the potential application of MOMs to improve the performance of commercial NLC, which require further future studies.

Cellulose-Based Stimuli-Responsive Anisotropic Hydrogel for Sensor Applications

Hydroxypropyl cellulose (HPC) is a hydroxypropylated derivative of cellulose with a lyotropic liquid crystal (LC) property and thermochromism. We introduced HPC into poly 2-acrylamido-2-methylpropane sulfonic acid (PAMPS), forming an anisotropic hydrogel by mechanical shearing. The polymerized long-range ordered HPC/PAMPS hydrogel shows a uniform interference color between crossed polarizers, which could be applied as a multifunctional sensor responding to temperature, pressure, and tensile force. In particular, the oriented HPC/PAMPS hydrogel, as a temperature sensor, can respond to a wide temperature range, and the vivid interference color change has little transmittance loss due to the confinement of a hydrogel network. This work may broaden the application areas of the anisotropic hydrogel and present inspirations into the multi-functional cellulose-based hydrogel sensors.

Determination of dielectric properties of 5CB nematic liquid crystal doped with new chiral calamitic compounds

Determination of dielectric properties of 5CB nematic liquid crystal doped with new chiral calamitic compounds

Enhanced electro-optical properties of nematic liquid crystal doped with Nitrogen doped graphene quantum dots

The first step of this study was to prepare mixtures that contained different concentrations of N doped graphene quantum dots (NGQDs) into nematic liquid crystals (NLCs). Then, through the Z-scan technology, the optical measurements in the nonlinear regime were conducted with a continuous wave (CW) at 632 nm wavelength and a low power laser beam. The nonlinear absorption (NLA) coefficient, nonlinear refractive (NLR) index, and third-order nonlinear susceptibility of NLCs doped with different concentrations of the NGQDs at distinctive laser powers and diverse applied voltages of external electric field was experimentally measured. The Z-scan results demonstrate that prepared cells have two photon absorption (2PA) and self-focusing effects. As the result, the concentration of the NGQDs in E7 and power of laser were optimum at 1% wt. and 11 mW, respectively. The effect of a DC electric field on optical nonlinearity was also investigated in the mixtures of NLCs and NGQDs at the concentration of 1% wt. Based on these findings, this sample can be used in both nonlinear optics and ultrafast broadband photonics.

Micro-scale viscosity measurements of different thermotropic and lyotropic classes of liquid crystals by using ferrofluid inclusions

Dispersing micro- and nanoparticles in liquid crystals (LCs) is utilised to tune liquid crystal properties, to add functionality or to exploit the self-organization of the liquid crystals to transfer order onto dispersed particles. Dispersing ferrofluid droplets in LCs produces a system similar to LC-microparticle dispersions, because the ferrofluid droplets behave in first approximation as non-compressible, only slightly deformable particles. Such a LC-ferrofluid system adds a magnetic functionality, which can be exploited to measure the viscosity and its anisotropy on a microscopic scale when moving the ferrofluid inclusions through various liquid crystals of the thermotropic, lyotropic or colloidal kind. Effective viscosities can be determined as a function of changing environment, such as temperature or concentration, and for variation of other factors such as the pitch of chiral phases for instance. The viscosities are calculated using Stokes’ Law together with the introduction of a boundary layer at the liquid crystal – ferrofluid interface. We present results for a variety of different liquid crystalline systems; thermotropic nematics, chiral nematics, smectics, lyotropic phases and chromonic systems, as well as colloidal LCs such as cellulose nanocrystals (CNC) and graphene oxide (GO) varying the viscosity over more than three orders of magnitude. The results are discussed in terms of the structures of respective phases.

The influence of gold nanoparticles on electro-optical properties of nematic liquid crystal

The influence of gold nanoparticles on electro-optical properties of nematic liquid crystal

Role of Hydroxy Group in the Electro-Optical Properties of Polymer-Dispersed Liquid Crystals

In this work, hydroxylated compounds are applied to prepare polymer-dispersed liquid crystal (PDLC) films and the role of the hydroxy group is studied in detail by comparing the effects of the hydroxylated acrylate monomer, the hydroxylated mesogenic component and their corresponding non-hydroxylated components. It is revealed that the hydroxylated acrylate monomer plays a more important role in modifying the morphology of the polymer matrix and thereby the electro-optical performance of the PDLC films. Parameters of the polymer matrix, such as size and density of voids, can be affected by various components, but only the hydroxylated acrylate monomer can alter its type from the typical Swiss-cheese type to the polymer-microsphere type. Essentially, the hydroxylated mesogenic component takes effect through changing the ratio of the liquid crystal phase, while the hydroxylated acrylate monomer can participate in the polymerization and impact the development of the polymer matrix. It is anticipated that this research can help in understanding the role of the hydroxy group in PDLC films.

Calibration-free method to study temperature dependence of microwave dielectric properties of nematic liquid crystals

ABSTRACTThe present article shows an original transmission-reflection-based method to characterise the microwave dielectric properties of liquid crystals. This new method offering broadband capabilities of transmission-reflection method without the need for vector network analyser calibration. It is based on two measurements in the frequency range: one measurement is performed with the empty cell, the other with the cell filled with the material. The analysis of the two recorded scattering matrices allows to eliminate all error terms and to extract real and imaginary parts of the complex dielectric constant. In this paper, we first present this method, its validation in comparison to other characterisation methods. Secondly, we present an appropriate measuring cell which allows measurements in the frequency range 26 GHz-40 GHz which is also well-suited for temperature-dependent measurements. This method is used to perform dielectric microwave measurements on 5CB liquid crystal. Finally, we discuss the temperature-dependent microwave dielectric properties (permittivity, losses and dielectric anisotropy).

Synthesis and characterisation of novel aromatic ester swallow-tailed cholesteric liquid crystal polymers

ABSTRACT In this paper, two novel aromatic ester swallow-tailed liquid crystal monomers M1 and M2 and a straight chain cholesteric liquid crystal monomer M3 were designed and synthesised. Two series of liquid crystal polymers, P1 series and P2 series, were graft-copolymerised with M and polymethylhydrosiloxane (PHMS). All the synthesised liquid crystal monomers and polymers were characterised by IR and 1H NMR and confirmed to the predicted molecular structure. The liquid crystal and thermal properties of the synthesised compounds were tested by DSC, POM, TGA and optical rotation. The results show that the monomer M1 is a monotropic nematic liquid crystal, and the Schlieren texture appears during the cooling process. M2 is an enantiotropic nematic liquid crystal with filamentous and schlieren texture. M3 is a thermotropic enantiotropic cholesteric phase with oily streak and focal cone texture. Both polymers P1 and P2 show typical Grand-Jean texture, and with the increase of monomer M3 content, the polymer clearing point temperature Ti increases continuously, the liquid crystal mesophase range widens, and the specific rotation value increases.

Synthesis, characterization and structure-mesomorphic properties relationship of palm-based azo-ester bridged liquid crystals from caprylic acid

This paper discussed the liquid crystal properties of a new homologous series derived from palm caprylic acid that differ in terms of terminal substituents. The chemical structures of synthesized compounds were characterized by nuclear magnetic resonance (NMR), fourier transform infrared (FT-IR) and CHN elemental analysis, while the mesomorphic behaviors were evaluated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The insertion of a polar substituent i.e. -CH3 (BME), -OCH3 (BMO), -OCH2CH3 (BEO) at the sixth position on the benzothiazole ring was able to reveal broad nematogenic temperature ranges (65.60–141.48 °C). The nematic mesophase stability is in order of BEO > BMO > BME, with two of them revealing their mesophase characteristics at nearly room temperature. This finding endorses a strong association between polarity factor and mesomorphism which was confirmed through density function theory with the basis set of 6–311 G d,p. The molecules also exhibit relatively high thermal stability (218–312 °C). This finding might be helpful in future structure design of palm-based LCs, as well as encourage the efforts in utilizing palm oil as a renewable and cheaper resource alternative, particularly in non-edible areas such as oleochemical-related research and development.

High thermal conductivity and excellent mechanical properties of liquid crystal co‐polyester based on hydron bond

AbstractHigh thermal conductivity liquid crystal polymer has become a hot topic in electronic device research. Herein, we introduce a series of thermotropic liquid crystals synthesized by diphenyl diol, m‐phthalic acid, and 5‐hydroxyisophthalic acid. The intermolecular forces are tuned by adjusting the ratio (0, 20%, 40%, 60%, 80%, 100%) of monomers containing hydrogen bond donors in copolymers. The formation and dissociation of hydrogen bonds are analyzed from the red shift and blue shift of infrared spectra at variable temperatures. The thermal conductivity is increased to 0.31 Wm−1 k−1. Meanwhile, its mechanical properties and thermal stability have improved significantly. A sharp increment of 2120% in tensile strength was observed, the maximum tensile strength is 17.39 MPa. While Young's modulus increased from 0.26 to 1.224 GPa. The increase in intermolecular forces is the main reason for this result. Moreover,X‐raysingle‐crystal diffraction, polarizing microscope, differential scanning calorimetry, and thermogravimetric analysis (TGA) were also analyzed to further explore the thermal conduction mechanism. The formation of hydrogen bonds makes the linear polymer chain segments undergo reversible cross‐linking, which affects their crystallization behavior and provides more thermal conduction pathways. By controlling the number of hydrogen bond donors to control the cross‐linking density, the thermal conductivity and mechanical properties can be greatly improved.

Preparation and properties of composite hydrogels for 3D bioprinting

AbstractBioprinted scaffolds have broad applications in the treatment of cardiovascular diseases. 3D bioprinting can prepare complex structures and shapes, and the fabrication of high‐performance bioinks is the key to technological progress. This study selected gelatin, chitosan quaternary ammonium salt, and sodium cromoglycate as substrates to design and characterize two groups of hydrogel materials for bioprinting. Two hydrogels were prepared by extrusion bioprinting: Gel/HACC/DSCG hydrogel and GelMA/HACC‐DSCG hydrogel. The physicochemical and liquid crystal properties of hydrogels were characterized. The effect of liquid crystal on cell proliferation and orientation was evaluated by culturing human umbilical vein endothelial cells. The Gel/HACC/DSCG hydrogels showed inducibility to orientated cell growth. The GelMA/HACC‐DSCG hydrogels had lesser damaged cells and stronger mechanical strength and stability in printing, however, the liquid crystal properties were weakened, and the effect on cell growth orientation was not significant.

Mesomorphic property and gelation ability of rod-shaped compounds having a coumarin skeleton

ABSTRACTRod-shaped liquid crystal materials with a lactone group at the terminal position of the molecule were designed, synthesised and their mesomorphic properties in bulk state and gelation ability in several organic solvents were examined. The effects of perfluoroalkyl chain and chemical structure on liquid crystal property and gelation ability were investigated. These compounds showed smectic A phase in bulk state and gelation ability in polar organic solvents. It was found that the presence of perfluoroalkyl chain and the direction of orientation of the esters had a great effect on these properties.

Fluorination improves the mesomorphic and photovoltaic performance of rod-like liquid crystal molecules

Molecular modification engineering is an important pathway to develop novel multifunctional materials. In this work, we designed and synthesized compounds nN-1, nSN, nFN and nFSN to study the fluorination effect on the mesomorphic and photovoltaic performance of rod-like liquid crystal (LC) molecules. Their chemical structures were confirmed, and the instruments of differential scanning calorimetry and polarising optical microscopy were employed to investigate their mesomorphic properties. Their photovoltaic performance was assessed using dye-sensitized solar cells (DSSCs). Meanwhile, experimental results were explained by using molecular steric configuration, frontier orbital and dipole moment from DFT calculations. Research results indicate that the fluorination not only decreases the melting points and enhances the nematic phase temperature ranges, but also effectively improves molar extinction coefficients, further increasing photocurrent density and achieving higher efficiency. This study provides a scientific basis and experimental data for molecular engineering strategies to conduct bifunctional materials combining the excellent properties of LCs and dye sensitizers.