Nematic Phase Research Articles

Liquid Crystalline Phases for Identification of new Ether organic compounds from Amoxicillin

Two series of compounds resulting from the reaction of alkoxy benzaldehyde with alkoxy amoxicillin were prepared. first series, five compounds were prepared by fixing alkoxy benzaldehyde with carbon atoms (6) with(butaoxy, pentaoxy, hexaoxy, heptaoxy, octakoxy) Amoxicillin, while second series, four compounds were also prepared by fixing alkoxy Amoxicillin with carbon atoms (6) with(butaoxy, pentaoxy, heptaoxy, octakoxy) benzaldehyde, and the necessary measurements were taken to verify the resulting compounds, such as (FTIR), (HNMR), and measurements Regarding the determination of liquid crystalline compounds by polarized light microscopy (POM), it was found that the presence of (nematic and smectic) phases in the case of cooling is in addition to the isotropic phase.

Effect of Quantum Dots Dispersion on the Structural, Optical, and Thermal Properties of Liquid Crystal System

Liquid crystal-quantum dot (LC-QD) composites are promising new materials for a number of applications in displays, energy harvesting, and photonics. In the present work, quantum dispersion in the mixture of LCs of cholesteric and nematic phases is reported. The combination of two LCs, namely Cholesteryl Palmitate (cholesteric 97%) and 4′-Pentyl-4-biphenylcarbonitrile (nematic, 98%), were used in equal proportion while CdS quantum dots were added in this mixture. The thermal, optical, and structural properties of this new LC-QD composite system were analyzed using differential scanning calorimetry (DSC), ultra-violet visible (UV-VIS) spectroscopy, Fabry-Perot scattering studies (FPSS), and Fourier transform infrared (FTIR) spectroscopy. Structural studies indicate that the QDs are uniformly dispersed inside the LC matrix rather than on the surface area. It was observed that quantum dot dispersion increases the strength of the LC mixture. It also changes the phase behavior of the LC mixture affecting the overall performance of LC-QD composite systems. The present findings would be very helpful for the design of the display and photonic devices with an improved optical response.

Investigation of phase transition in the binary mixture of thermotropic liquid crystalline systems 4-(Heptylox) benzoic acid and 4-(Undecyloxy) benzoic acid using Raman and DFT studies

A binary mixture Uba@Hba of liquid crystalline systems; 4-(Undecyloxy) benzoic acid and 4-(Heptylox) benzoic acid was prepared, and their liquid crystalline properties were investigated through differential scanning calorimetry and polarized optical microscopy at the bulk level and temperature dependent Raman spectroscopic technique as well as density functional calculations at molecular level. The polarized optical microscopic studies revealed crystal, smectic A, nematic and isotropic phases in the Uba@Hba. The phase transition temperatures of the binary mixture Uba@Hba was identified by the temperature dependent Raman study which was found almost close to phase transitions observed in differential scanning calorimetry and polarized optical microscopy. The detailed Raman & DFT studies provide information occurring in phase transitions at molecular level. The changes in inter/intra-molecular interactions at crystal → smectic A and smectic A → nematic transitions have been discussed in detail.

Unlocking the potential of 2,1,3-benzoxadiazole-based luminescent liquid crystals

ABSTRACT Here, we report the synthesis and characterisation of 2,1,3-benzoxadiazole-based (BOX) luminescent liquid crystals with a π-conjugated core and different elongated donor units connected by triple bonds. These molecules exhibited calamitic thermotropic mesomorphism with nematic and smectic phases and intense photoluminescence under UV–vis light excitation in solutions and films. In solution, the emission revealed a maximum in the yellow region (502 to 590 nm), similar to that of benzothiadiazoles (BTD) homologous, but with fluorescence quantum, it yields significantly higher (ΦPL = 0.30–54). The nature of donor unit substantially influenced the quantum yields and excited state lifetimes. Solvatochromism studies showed a dependence of the emission, quantum yield and lifetimes with the polarity of the solvent. This work demonstrates that 2,1,3-benzoxadiazole core derivatives have thermal and photophysical properties similar to BTDs but with superior quantum efficiency.

Hidden scale invariance in the Gay-Berne model. II. Smectic-B phase.

This paper complements a previous study of the isotropic and nematic phases of the Gay-Berne liquid-crystal model [Mehri et al., Phys. Rev. E 105, 064703 (2022)2470-004510.1103/PhysRevE.105.064703] with a study of its smectic-B phase found at high density and low temperatures. We find also in this phase strong correlations between the virial and potential-energy thermal fluctuations, reflecting hidden scale invariance and implying the existence of isomorphs. The predicted approximate isomorph invariance of the physics is confirmed by simulations of the standard and orientational radial distribution functions, the mean-square displacement as a function of time, and the force, torque, velocity, angular velocity, and orientational time-autocorrelation functions. The regions of the Gay-Berne model that are relevant for liquid-crystal experiments can thus fully be simplified via the isomorph theory.

Synthesis, mesomorphic and fluorescent properties of stilbene-containing 1,3,4-oxadiazole compounds

ABSTRACT A new class of mesogenic 1,3,4-oxadiazole derivatives 2a-2e based on stilbene has been synthesised and characterised by means of nuclear magnetic resonance (NMR), electro spray ionisation-mass spectrometry (ESI-MS) techniques and elemental analyses. The thermal properties were investigated by means of differential scanning calorimetry (DSC), polarising optical microscopy (POM) and thermogravimetric analyses (TGA). All compounds exhibited enantiotropic liquid crystal behaviours with typical calamitic mesophases (Smectic A (SmA), Smectic C (SmC) and Nematic phases) in very wide temperature range with excellent thermal stability. The nature of the mesophase is determined greatly by the polarity of the terminal groups. The electron-withdrawing cyano (for 2a) and fluoro (for 2b) groups tended to form smectic A phase, while the electron-donating methyl (for 2c), methoxy (for 2d) and decyloxy (for 2e) groups facilitated the SmA or SmC and nematic phases. Out of expectation, no banana phases were found in these mesogens. It’s noted that the solutions of all compounds in CH2Cl2 individually displayed one absorption band with λmax values at 340–355 nm, and exhibited an intense emission with λmax values at 428–486 nm and photoluminescence quantum yields of 0.39–0.55. The relationship between the molecular structures and mesogenic properties is discussed briefly in this work.

Gelled lyotropic nematic liquid crystals

ABSTRACT Lyotropic liquid crystal gels (LLC gels) are versatile materials which combine the anisotropy of a liquid crystal with the mechanical stability of a gel. We succeeded in gelling the rare calamitic nematic NC phase of two different micellar LLC systems with the low molecular weight gelator (LMWG) 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). The systems of choice are: (1) a binary LLC system with the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water; (2) a ternary LLC system with the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), n-decanol, and water. The obtained gels show optical birefringence and no macroscopic flow. Freeze fracture electron microscopy (FFEM) images show ribbon-like gel fibres that form the gel network and can stack into thicker bundles, while small-angle X-ray scattering (SAXS) confirms the coexistence of the nematic NC phase and the gel network. The growth of the gel network was monitored with time-resolved SAXS measurements. Additionally, significant gel ageing effects were observed in rheology measurements, showing that the gel strengthens with time. With this study, we considerably broaden the pool of available surfactant-based LLC gels and pave a way to macroscopically aligned LLC gels with the goal to apply them as stimuli-responsive actuators and sensors.

Exotic liquid crystalline phases in monolayers of vertically vibrated granular particles

ABSTRACTVibrated monolayers of granular particles confined into horizontal cavities form a variety of fluid patterns with orientational order that resemble equilibrium liquid-crystal phases. In some cases, one can identify nematic and smectic patterns that can be understood in terms of classical statistical mechanics of hard bodies. Low aspect ratio cylinders project as rectangles and form uniaxial, or 2-atic, and tetratic, or 4-atic, nematic phases. Other polygonal particles may exhibit different liquid-crystal phases, in general p-atic phases, of higher symmetries. We give a brief summary of theoretical work on rectangles and triangles, and provide some experimental results on vibrated monolayers. In the case of equilateral triangles, the theory predicts an exotic triatic phase, or 6-atic phase, with six-fold symmetry and three equivalent directors. The right-angled triangles exhibit a 4-atic phase with strong octatic (8-atic) correlations. Experiments on cylinders show 4-atic textures and, even more remarkable, geometric frustration caused by confinement excites topological defects, which seem to follow the same topological rules as standard liquid crystals. Some of our findings can be understood with the help of simulations of hard particles subject to thermal equilibrium, although standard Density-Functional Theories fail to account for the correct equilibrium phases in some cases.

A series of liquid crystalline acrylic polymers obtained by a novel electrically induced polymerization method

The synthesis and phase characterization of a homologous series of polymers possessing high molecular weight of acrylic phenyl benzoates has been carried out using a novel polymerization method. The characterization comprises polarized optical microscopy, differential scanning calorimetry and wide-angle X-ray scattering. All polymers are mesogenic, exhibiting either nematic and/or smectic phase depending on chain length. Polymers phases are enantiotropic unlike the starting monomers which are predominantly monotropic. Shorter monomers yield nematogenic and monolayer smectogenic polymers while longer monomers yield polymers with a tilted bilayer smectogenic character. The transition from monolayer to bilayer was observed when a monomer with a terminal chain length of five carbon atoms was polymerized.

Nematic-isotopic phase separations induced by hydrogen bonding between a rodlike polymer and solvent molecules

ABSTRACT We theoretically study nematic-isotropic phase transitions and phase separations in aqueous rodlike polymer solutions, such as rigid DNA (or rodlike polymer) in water. By taking into the hydrogen bonding between a rodlike polymer and solvent molecules, we predict novel phase diagrams, such as overhang-type coexistence curves with isotropic-nematic ( I + N ) phase separations and re-entrant I + N separations. We demonstrate that the hydrogen bonding between molecules of different components stabilises the nematic phase at lower polymer concentrations and temperatures.

Design of New V Shaped Thermotropic Liquid Crystals containing Heterocyclic

The characterization and design of this study of new liquid crystals with a V shape compounds containing thiazolidine-2,4-dione and 1,3-phenylene as a core unite with mesophase properties were reported. Preparation and characterization of chloroacetic acid, water, and thiourea to produce thiazolidine-2,4-dione [I] in the presence of strong hydrochloric acid. The 4-hydreoxybenzaldehyde and n-alkyl bromide were reacted with potassium hydroxide to create the n-alkoxy benzaldehyde., then the compound [I] reacted with [II]n in presence of piperidine to produce compounds [III]n. Also, converted resorcinol to a corresponding compound [IV] by refluxing pyridine and DMF with two moles of chloracetyl chloride, after that interacted the compounds [III]n and compound [IV] with sodium acetate to form compounds [V]n. FT-IR and 1HNMR spectroscopy were really used to determine the structures of the produced substances. Using polarized optical microscopy, these mesogens' mesomorphic characteristics were studied (POM).The synthesized molecules exhibited enantiotropic liquid crystal phases, the substances [V]1-4 exhibited an only the enantiotropic nematic phase.

Enhancement of electro-optical properties and phase transition temperature of thermotropic liquid crystal 5CB by doping with 4-n-pentylbenzoic acid

ABSTRACT Liquid crystalline materials that have been used in the display industry need to have a wide temperature-range nematic phase while remaining functioning in different climate conditions. In this work, a new binary mixture of thermotropic liquid crystal materials, particularly the nematic phase, has been studied. A widely used material 5CB (4-Cyano-4’−pentyl biphenyl), exhibiting nematics phase, and PA (4-Phenylbenzoic acid) were preferred. Mixtures of different concentrations of 5CB-PA were prepared and investigated using dielectric spectroscopy, phase transition and electro-optical responses techniques. It was found that not only was an improvement to the dielectric anisotropic achieved but also the nematic temperature range extended from 35 ºC to just above 50°C by adding 10 wt.%. On the other hand, the threshold voltage is increased by 10% for the same sample. In addition, elastic constants and response time showed similar behaviours upon increasing the loading concentration of PA, whereas the visco-elastic coefficient significantly declined. All the estimated values for the pure 5CB are in good agreement with the literature. This improvement in the operating temperature range is unique and suggests that the doping can lead to cheap and mass production of a stable liquid crystalline material for their application in the display industry.

Near-continuous isotropic – nematic transition in compressed rod-like liquid crystal based nanocolloid

Landau-de Gennes mean-field model predicts the discontinuous transition for the isotropic – nematic (I-N) transition, associated with uniaxial ordering and a quadrupolar order parameter in three dimensions. This report shows pressure-related dielectric studies for rod-like nematogenic pentylcyanobiphenyl (5CB) and its nanocolloids with BaTiO3 nanoparticles. The scan of the dielectric constant revealed the near-continuous I-N phase transition in the compressed nanocolloid with a tiny amount of nanoparticles (x = 0.1%).For the nematic phase in 5CB and its x = 1% nanocolloid the enormous values of the dielectric constant and the bending–type, long-range pretransitional behavior were detected. The impact of prenematic fluctuations was also noted for the ionic-related contribution to dielectric permittivity in the isotropic liquid phase. For the high-frequency relaxation domain, this impact was tested for the primary relaxation time pressure evolution and the translational–orientational decoupling.

Manifestation of spin nematic ordering in the spin-1 chain system

Spin-1 chain material is considered. Recently, it was predicted that the spin nematic ordered phase can be realized due to the spin-elastic coupling. In this study we show that the appearance of the spin nematic ordering and phase transitions to such ordered states can be studied using magneto-acoustic experiments. One can observe such phases and phase transitions considering relative changes of the velocity of sound (related to the changes of the elastic modulus of the crystal) as a function of temperature and the external magnetic field. It is shown that those relative changes are proportional to the spin quadrupole susceptibility of the system. The results are obtained using the exact Bethe ansatz solution and Quantum Monte Carlo simulations for several typical values of the biquadratic spin-spin exchange interaction and for various values of the spin-elastic coupling and elastic modules.

Walking Ferroelectric Liquid Droplets with Light.

The motion of ferroelectric liquid sessile droplets deposited on a ferroelectric lithium niobate substrate can be controlled by a light beam of moderate intensity irradiating the substrate at a distance of several droplet diameters from the droplet itself. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on the side of the lithium niobate exposed to light irradiation. Moreover, moving the beam results in walking the ferroelectric droplet over long distances on the substrate. This behavior is understood as due to the coupling between the polarization of the ferroelectric droplet and the polarization photoinduced in the irradiated region of the lithium niobate substrate. Indeed, the effect is not observed in the conventional nematic phase, suggesting the crucial role of the ferroelectric liquid crystal polarization.

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.

Pair correlation functions and stability of nematic in a system of Gay-Berne ellipsoids doped with spherical colloids

Pair-structure of a binary mixture of soft-ellipsoids and spheres interacting via generalized Gay-Berne intermolecular potential using Percus–Yevick (PY) integral equation theory. The generalized Gay-Berne interaction model allows us to vary the diameter of the spheres in comparison to the width of the Gay-Berne ellipsoids. Three different cases of sphere size namely diameter of the spheres being smaller, equal and larger than the minor axis of the ellipsoids have been considered. We have analyzed the radial distribution functions and static structure factors of the mixtures and found that addition of spherical particles to a system of ellipsoids results in stronger pair-correlations between ellipsoidal particles. We observe that smaller spherical additives are more effective in enhancing the ellipsoidal pair-correlations in comparison to the bigger spheres at similar density.The static structure factors are not found to diverge in the low wavelength limit indicating a stable mixture for the set of parameters studied in this work. We have also used classical density functional theory of freezing to investigate the effect of spherical additives and their size on the isotropic-nematic phase transition. We found a stable nematic phase whose order parameter is found to increase with the increase in not only the density of spherical additives but also with increase in their size.

Nematic single-component superconductivity and loop-current order from pair-density wave instability

We investigate the nematic and loop-current type orders that may arise as vestigial precursor phases in a model with an underlying pair-density wave (PDW) instability. We discuss how such a vestigial phase gives rise to a highly anisotropic stiffness for a coexisting single-component superconductor with low intrinsic stiffness, as is the case for the underdoped cuprate superconductors. Next, focusing on a regime with a mean-field PDW ground state with loop-current and nematic $xy$ (B$_{2g}$) order, we find a preemptive transition into a low and high-temperature vestigial phase with loop-current and nematic order corresponding to $xy$ (B$_{2g}$) and $x^2-y^2$ (B$_{1g}$) symmetry respectively. Near the transition between the two phases, a state of soft nematic order emerges for which we expect that the nematic director is readily pinned away from the high-symmetry directions in the presence of an external field. Results are discussed in relation to findings in the cuprates, especially to the recently inferred highly anisotropic superconducting fluctuations [W{\aa}rdh {\em et al.}, ``Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide'', arXiv:2203.06769], giving additional evidence for an underlying ubiquitous PDW instability in these materials.

Chiral Chromonics Confined in Spherical Geometries

Chromonic liquid crystals have recently received a lot of attention due to their spontaneous self-assembly in supramolecular columnar structures that, depending on their concentration in water, align to form a nematic liquid crystalline phase. The chirality may be induced in chromonics by adding chiral moieties to the nematic phase or enhanced by confining them in curved geometrical constraints. This review summarizes the recent research developments on chiral chromonic liquid crystals confined in spherical geometry, relating the results to what was observed for thermotropic liquid crystals in the same conditions. The review focuses on the studies carried out on commercially available nematic chromonics, investigating the effects on their topologies in different anchoring conditions and different chiral dopants and suggesting an application in the sensor field.

Molecular Shape, Electronic Factors, and the Ferroelectric Nematic Phase: Investigating the Impact of Structural Modifications.

The synthesis and characterisation of two series of low molar mass mesogens, the (4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3.m) and the (3-fluoro-4-nitrophenyl) 2-alkoxy-4-(4-methoxybenzoyl)oxybenzoates (NT3F.m), are reported in order to investigate the effect of changing the position of a lateral alkoxy chain from the methoxy-substituted terminal ring to the central phenyl ring in these two series of materials based on RM734. All members of the NT3.m series exhibited a conventional nematic phase, N, which preceded the ferroelectric nematic phase, NF , whereas all the members of the NT3F.m series exhibited direct NF -I transitions except for NT3F.1 which also exhibited an N phase. These materials cannot be described as wedge-shaped, yet their values of the ferroelectric nematic-nematic transition temperature, T , exceed those of the corresponding materials with the lateral alkoxy chain located on the methoxy-substituted terminal ring. In part, this may be attributed to the effect that changing the position of the lateral alkoxy chain has on the electronic properties of these materials, specifically on the electron density associated with the methoxy-substituted terminal aromatic ring. The value of TNI decreased with the addition of a fluorine atom ortho to the nitro group in NT3F.1, however, the opposite behaviour was found when the transition temperatures of the NF phase were compared which are higher for the NT3F.m series. This may reflect a change in the polarity and polarizability of the NT3F.m series compared to the NT3.m series. Therefore, it is suggested that, rather than simply promoting a tapered shape, the role of the lateral chain in inhibiting anti-parallel associations and its effect on the electronic properties of the molecules are the key factors in driving the formation of the NF phase.