Improvement of the electro-optical properties of nematic liquid crystals doped with strontium titanate nanoparticles at various doping concentrations

ABSTRACT

In this study, we doped homogenous aligned nematic liquid crystal (NLC) systems with strontium titanate (SrTiO₃) nanoparticles (NPs), and investigated the impact of doping concentration on the NLC’s electro-optical (EO) properties. SrTiO₃ NP-doped NLC cells maintained a high optical transmittance of 77.51% to 78.41% compared to pure NLC cells (78.09%). At a 0.1 wt.% SrTiO₃ NP doping concentration, twisted-nematic (TN)-LC cells exhibited enhanced EO performance, with a reduced threshold voltage from 1.70V to 1.61V and a shorter response time from 17.03 ms to 10.66 ms without optical defects and degradations. We also observed an improvement in thermal endurance for doping concentrations of 0.05 and 0.1 wt.%.     

Highly improved dielectric behaviour of ferronematic nanocomposite for display application

We report the investigation of influence of nickel zinc ferrite magnetic nanoparticles (NZFO (Ni_0.5Zn_0.5Fe₂O₄)) on phase transition, optical and dielectric properties in a nematic liquid crystal (NLC). The interaction of NZFO nanoparticles with NLC was confirmed by the formation of ferronematic droplets due to the transfer of magnetic orientational effect onto the underlying NLC matrix. The doping results in shift of nematic to isotropic transition to low-temperature region. An enhancement in the value of refractive index is observed in the nematic region after the addition of NZFO nanoparticles. The dielectric constant of NLC was remarkably enhanced by 10 times after doping, which is found to be maximum at 0.1 wt% concentration of NZFO nanoparticles. The decrease in the value of dissipation factor in low-frequency region shows that the magnetic nanoparticles are able to trap ionic impurities effectively. The obtained results suggest that the optimum amount of doping concentration is 0.1 wt% of NZFO nanoparticles in NLC due to high dielectric constant with low dissipation factor and high refractive index with high dispersive power at room temperature.     

Superior electro-optic properties of liquid crystal system using cobalt oxide nanoparticle dispersion

In this article, we study the electro-optical (EO) properties of the homogeneous aligned nematic liquid crystal (N-LC) doped with cobalt oxide (Co₃O₄) nanoparticles (NPs). The EO characteristics of Co₃O₄ doped N-LC are higher performance, indicating lower threshold voltage (1.33 V), faster rising time (1.479 ms), and faster falling time (9.343 ms) than pure liquid crystal (LC) cells. We have demonstrated these results by investigating the relationship between dielectric constants and LC device properties. Furthermore, we proved NPs doped N-LC cells drive low power operation without capacitance hysteresis. Our experimental results were verified by software simulation based on general physical properties.     

Analysis of electro-optical and dielectric parameters of TiO2 nanoparticles dispersed nematic liquid crystal

The present investigation is focused on to find out the role of TiO₂ nanoparticles (NPs) on altering the dielectric and electro-optical parameters of nematic liquid crystal (NLC). In addition to this, we also optimized the concentration of dopant (0.25 wt%) for a saturation value of permittivity and dielectric anisotropy in the doped system. Dielectric spectroscopy has been performed with the variation of frequency and temperature to investigate the various dielectric parameters, which demonstrate that the investigated NLC is of positive dielectric anisotropy; the observed result shows a decrement in the value of relative permittivity and dielectric anisotropy; however, the permittivity value increases for higher concentration of dopant but remains less than that of pure NLC. Electro-optical measurements have also been performed to compute the optical response of pure and dispersed NLC. It is found that optical response decreases for the NP-doped systems. This optimized concentration of NPs in NLC matrix can have various credential applications in the field of active matrix display and holography.     

Novel Synthesis of CeO2 Nanoparticles Within Formamide/Tri(ethyleneglycol)monododecyl Ether/n-Octane Nonaqueous Microemulsion Systems

The present study evaluates a new method to prepare Cerium oxide (CeO₂) nanoparticles by formamide/tri(ethyleneglycol)monododecyl ether (C₁₂E₃)/n-octane oil-continuous nonaqueous microemulsion. The effect of the polar phase (formamide/water) on the phase behavior, drop size, and conductivity behavior of the reverse microemulsion were investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase and morphology of synthesized CeO₂ nanoparticles. It was found that the CeO₂ powders synthesized within nonaqueous microemulsions and aqueous microemulisons had an average particle size of 30–50 nm and 15–40 nm, respectively. The experimental results indicate the formation mechanism of CeO₂ nanoparticles in formamide nonaqueous microemulsion and aqueous microemulsion is similar, and the formamide nonaqueous microemulsion can be used as nanoreactors for preparation of nanoparticles.     

Bio-therapeutic Potential and Cytotoxicity Assessment of Pectin-Mediated Synthesized Nanostructured Cerium Oxide

In the present studies, renewable and nontoxic biopolymer, pectin, was extracted from Indian red pomelo fruit peels and used for the synthesis of cerium oxide nanoparticles (CeO₂-NPs) having bio-therapeutic potential. The structural information of extracted pectin was investigated by FTIR and NMR spectroscopic techniques. Physicochemical characteristics of this pectin suggested its application in the synthesis of metal oxide nanoparticles. Using this pectin as a template, CeO₂-NPs were synthesized by simple, one step and eco-friendly approach. The UV–Vis spectrum of synthesized CeO₂-NPs exhibited a characteristic absorption peak at wavelength 345 nm, which can be assigned to its intrinsic band gap (3.59 eV) absorption. Photoluminescence measurements of CeO₂-NPs revealed that the broad emission was composed of seven different bands. FTIR analysis ensured involvement of pectin in the formation and stabilization of CeO₂-NPs. FT-Raman spectra showed a sharp Raman active mode peak at 461.8 cm^?1 due to a symmetrical stretching mode of Ce–O vibration. DLS, FESEM, EDX, and XRD analysis showed that the CeO₂-NPs prepared were polydispersed, spherical shaped with a cubic fluorite structure and average particle size ≤40 nm. These CeO₂-NPs displayed broad spectrum antimicrobial activity, antioxidant potential, and non-cytotoxic nature.     

Performance improvement in chemical oxygen demand determination using carbon fiber felt/CeO<Subscript>2</Subscript>-β-PbO<Subscript>2</Subscript> electrode deposited by cyclic voltammetry method

A three-dimensional (3D) structured electrode in which a compact CeO₂-β-PbO₂ particle layer on each carbon fiber in the felt (denoted as CF/CeO₂-β-PbO₂) was fabricated using cyclic voltammetry (CV) method in the presence of CeO₂ nanoparticles in the electrolyte and supposed to be used as a sensor for in situ chemical oxygen demand (COD) detection. It was found that CeO₂ was codeposited with PbO₂ onto the anode, and the deposited crystals were tiny and compacted with each other. The electrochemical behaviors demonstrate that the fabricated CF/CeO₂-β-PbO₂ electrode possesses larger effective surface area, higher electrochemically catalytic activity, and better mechanical stability as compared with the anode without CeO₂ deposited by CV method or constant potential (CP) method. The results of COD determination by the fabricated CF/CeO₂-β-PbO₂ electrode show a sensitivity of (3.0 ± 0.02) × 10^?3 mA cm^?2/mg L^?1, a detection limit of 3.6 mg L^?1 (S/N = 3) and a linear range of 30–8500 mg L^?1 with correlation coefficient (R) of 0.9985 and RSD within 5 %.

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Graphical abstract A 3D CF/CeO₂-β-PbO₂ electrode with CeO₂-β-PbO₂ particle layer on each carbon fiber in the felt was supposed to be used as a sensor for in situ chemical oxygen demand (COD) detection. It was fabricated by cyclic voltammetry (CV) method in the presence of CeO₂ nanoparticles in the electrolyte containing Pb²⁺. It was found that CeO₂ was codeposited with PbO₂ onto the anode and the deposited particles became tinier and more compact. The addition of CeO₂ enhances the electrochemical catalytic activity. Tinier and more compact crystals enlarge the effective electrode area and improve the mechanical strength, which makes the CF/CeO₂-β-PbO₂ electrode possess higher detection sensitivity, wider linearity range, and longer service life in COD detection as compared with the anodes without CeO₂ fabricated by CV method or constant potential (CP) method.

     

Synthesis, Characterization, Photoluminescence and Photocatalytic Properties of CeO2 Nanoparticles by the Sonochemical Method

Uniform CeO₂ nanoparticles were synthesized via a facile sonochemical reaction between ceric ammonium nitrate and ammonia. Nanoparticles were synthesized via a surfactant free reaction at room temperature in solvent of water. Products were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence (PL) spectroscopy, and energy dispersive X-ray analysis. The effect of different parameters such as precursor, power of pulsation, surfactant and reaction time on the morphology of the products was investigated. It was found that the as-obtained CeO₂ nanoparticles exhibit a strong PL peak at 381 nm at room temperature that can be ascribed to the high level transition in the CeO₂ semiconductor. The photocatalytic behavior of CeO₂ nanoparticles was evaluated using the degradation of a methyl orange aqueous solution under ultraviolet light irradiation. The results show that CeO₂ nanoparticles are promising materials with excellent performance in photocatalytic applications.     

Facile preparation of vanadium oxide thin films on sapphire(0001) by sol–gel method

The Ba_0.6Sr_0.4TiO₃ (BST60) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method. The thickness of CeO₂, serving as a buffer layer, was varied from 0 to 75 nm, in order to optimize the dielectric tunable property. X-ray patterns analysis indicates that all the thin films exhibit good crystalline quality with a pure perovskite phase and insertion of the CeO₂ buffer layer does not change the crystal structure of BST60. Dielectric properties of the thin films were investigated as a function of both temperature and direct current electric field. The results show that dielectric constant and loss are modified by insertion of the CeO₂ buffer layer. The BST60 thin films with 25 nm thickness CeO₂ buffer layer have the highest figure of merit, low dielectric loss, and suitable dielectric constant, which render them attractive for the tunable microwave device applications.     

Enhancement of flexoelectric ratio of nematic liquid crystal by doping calamitic ferroelectric liquid crystal

We measured the flexoelectric ratio e* of a nematic liquid crystal (NLC) doped with a calamitic ferroelectric liquid crystal (FLC). We doped two kinds of commercial FLC into the pure NLC at a weight concentration of 5 wt%. The absolute value of the flexoelectric ratio was increased up to 49% compared to the pure NLC. The greater transverse dipole moment and the elastic constant of FLC are thought to be related to the increase of the flexoelectric ratio.     

Effects of peak current density on the structure and property of PbO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> nanocomposite electrodes prepared by pulse electrodeposition

PbO₂–CeO₂ nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO₂ nanoparticles with different peak current density. The content of CeO₂ nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO₂–CeO₂ nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO₂–CeO₂ nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO₂–CeO₂ nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO₂–CeO₂ nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO₂ content in the composite electrodes.     

CeO<Subscript>2</Subscript> nanoparticle-modified electrode as a novel electrochemical interface in the quantification of Zn<Superscript>2+ </Superscript>ions at trace level: application to real sample analysis

A simple strategy has been proposed to quantify Zn²⁺ ions using CeO₂ nanoparticle-modified glassy carbon electrode. The CeO₂ nanoparticles were prepared by sucrose-nitrate decomposition method, and it was characterized by X-ray diffraction (XRD), FT-IR, TEM, and surface area analyzer. The synthesized CeO₂ nanoparticles were used as modifier molecules as a thin film on glassy carbon electrode (GCE) in the trace level quantification of Zn²⁺ by using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) techniques. The fabricated sensor exhibited a good analytical response towards Zn²⁺ ions. The modified electrode showed a wide linearity in the concentration range 20–380 μg L^?1 with a limit of detection 0.36 μg L^?1. The proposed electrochemical sensor was successfully applied to trace level Zn²⁺ quantification from real sample matrices.     

Ionic impurities in nematic liquid crystal doped with quantum dots CdSe/ZnS

We investigated the dielectric losses and the ionic currents in the nematic liquid crystal (NLC) doped with semiconductor quantum dots (QDs) of CdSe/ZnS core – shell type and covered with trioctylphosphine oxide (TOPO) molecules. The dielectric loss tangent of the NLC composites increased with increasing the QDs concentration from 0.1 to 0.3 wt%. The density of mobile ions in the composites increased linearly and the average values of ions mobility in the composites decreased with increasing the QDs concentration. The fast ions with the mobility of about 10^–10 m²/V·s and the slow ions with the mobility of about 10^–11 m²/V·s were detected in the NLC composites. The growth of the content of slow ions took place with increasing the QDs concentrations. Increasing the dielectric loss tangent was observed with increasing the duration of sonication time of the NLC composites to prepare homogeneous suspensions. The fragmentation of the CdS/ZnS shell as a result of the sonication may lead to the appearance of the slow ions in the NLC composites.     

Synthesis and liquid crystalline properties of substituted 2,5‐diaryl 1,3,4‐oxadiazole derivatives without flexible chains

A series of new compounds based on aromatically 2,5‐disubstituted 1,3,4‐oxadiazoles without flexible chains, formulated as p‐R–C₆H₄–(OC₂N₂)–(p‐C₆H₄)₂–R′ with (i) R = CH₃O, R′ = CH₃O, CH₃S, F, H (Ia–Id), (ii) R = CH₃S, R′ = CH₃O, CH₃S, F, H (IIa–IId) and (iii) R = F, R′ = CH₃O, CH₃S, F, H (IIIa–IIId) (p‐C₆H₄ and OC₂N₂ represent a p‐phenylene spacer and a 1,3,4‐oxadiazole ring, respectively), were synthesised and characterised by ¹H and ¹³C NMR, MS and HRMS techniques. Mesomorphic properties were investigated using differential scanning calorimetry and polarizing optical microscopy. All of the target compounds (except Id, IId, IIIc and IIId) exhibited an enantiotropic nematic mesophase with high melting temperatures. The liquid crystalline properties of these compounds were influenced greatly by polarity, steric factors and positions of the terminal groups. The effect of the terminal groups on the liquid crystal properties is discussed.     

Dye-dependent studies on droplet pattern and electro-optic behaviour of polymer dispersed liquid crystal

In order to study the droplet pattern and electro-optic (EO) behaviour of polymer dispersed liquid crystal (PDLC) with the addition of dye, dichroic polymer dispersed liquid crystal (DPDLC) films were prepared using a nematic liquid crystal (NLC), photo-curable polymer (NOA 65) and anthraquinone blue dichroic dye (B2), in equal ratio (1:1) of polymer and liquid crystal (LC) by polymerisation induced phase separation (PIPS) technique. Dichroic dye was taken in different concentration (wt./wt. ratio) as 0.0625%, 0.125%, 0.25%, 0.5% and 1% of the LC mixture in DPDLC films. Initially, in an open circuit when there is no proviso for external electric field (0 V), LC droplets in polymer matrix exhibited bipolar pattern, though on closing the circuit with the increase of electric field pattern of droplets starts changing, LC molecules align along the direction of applied electric field and aligned completely relatively at higher field (30 V), which illustrate vertical radial pattern. Further, results show that the DPDLC film containing 0.0625% dye concentration with consistent average droplet size ~4.30 μm, exhibits the best transmission at lower operating voltage.     

Preparation and electrochemical characterization of Ruddlesden–Popper oxide La4Ni3O10 cathode for IT-SOFCs by sol–gel method

La₄Ni₃O₁₀ oxide was synthesized as a cathode material for intermediate-temperature solid oxide fuel cells by a facile sol–gel method using a nonionic surfactant (EO)106(PO)70(EO)106 tri-block copolymer (F127) as the chelating agent. The crystal structure, electrical conductivity, and electrochemical properties of La₄Ni₃O₁₀ were investigated by X-ray diffraction, DC four-probe method, electrochemical impedance spectra, and I–V measurements. The La₄Ni₃O₁₀ cathode showed a significantly low polarization resistance (0.26 Ω cm²) and cathodic overpotential value (0.037 V at the current density of 0.1 A cm^?2) at 750 °C. The results measured suggest that the diffusion process was the rate-limiting step for the oxygen reduction reaction. The La₄Ni₃O₁₀ cathode revealed a high exchange current density value of 62.4 mA cm^?2 at 750 °C. Furthermore, an anode-supported single cell with La₄Ni₃O₁₀ cathode was fabricated and tested from 650 to 800 °C with humidified hydrogen (～3 vol% H₂O) as the fuel and the static air as the oxidant. The maximum power density of 900 mW cm^?2 was achieved at 750 °C.     

Direct Electrochemistry of Hemoglobin in Cerium Dioxide/Carbon Nanotubes/Chitosan for Amperometric Detection of Hydrogen Peroxide

Abstract

A novel hemoglobin (Hb) biosensor based on the remarkable synergistic effects of cerium dioxide (CeO₂) and multiwalled carbon nanotubes (MWNTs) for detection of hydrogen peroxide (H₂O₂) is presented. The Hb/CeO₂/MWNTs/CHIT nanocomposite was nanoengineered by selected matched material components and optimized composition ratio to produce a superior H₂O₂ sensor. The preparation method is quite simple and practical. This composite matrix combined the advantages of MWNTs, CeO₂ nanoparticles, and chitosan (CHIT), with good electron-transfer ability, attractive biocompatibility, and fine film-forming ability, which could increase Hb attachment quantity and H₂O₂ detection sensitivity. In the optimum pH 7.0 phosphate buffer, the electrocatalytic response exhibited a linear dependence on H₂O₂ concentration in a wide range from 5.0 × 10^?6 to 4.6 × 10^?4 mol L^?1 with a detection limit of 6.5 × 10^?7 mol/L (3σ).     

Initial corrosion behavior of composite coatings obtained by co-electrodeposition of zinc with nanoparticles of Ti and Ce oxides

The present work reports the results obtained for the electrodeposition of composite Zn coatings on steel by using Ti and Ce oxides nanopowders, separately or in mixture, and a TiO₂·CeO₂ binary oxide. In an attempt to correlate the effects of nanoparticles on corrosion behavior of the composite deposits, the properties of Zn–TiO₂·CeO₂ layers were compared with those referring to similar coatings prepared by using a simple mixture of the two oxides or individual oxides. Corrosion measurements were performed in 0.2 g?L^?1 Na₂SO₄ solution (pH?=?5). The results of electrochemical measurements (open circuit potential measurements, polarization curves, and electrochemical impedance spectroscopy) were corroborated with those obtained by using X-ray diffraction, atomic force microscopy, scanning electron microscopy, and salt spray tests. The results indicate that the composite Zn–(TiO₂?+?CeO₂) coatings exhibit the highest corrosion resistance from all investigated Zn coatings.     

Mechanical,thermal, and ultraviolet resistance properties of polycarbonate/cerium oxide composites

The composites containing polycarbonate (PC) and cerium oxide (CeO₂) nanoparticles as well as nanoparticles modified with stearic acid (mCeO₂) have been prepared using a melt blending method. The composites are studied by using FTIR spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and scanning electron microscopy, and their tensile strength and ultraviolet (UV) resistance are examined. The results indicate that the introduction of CeO₂ nanoparticles at 1 wt% can improve the mechanical properties of PC, while a weight ratio that is over 1 wt% can lead to a reduction in the tensile strength. Compared with the PC/CeO₂ composites, the PC/mCeO₂ composites provide better mechanical properties. Besides, the introduction of CeO₂ nanoparticles gives PC promising UV resistance. However, different amounts of CeO₂ nanoparticles used provide similar thermal and UV resistance in PC. In a comparison of the PC/CeO₂ and PC/mCeO₂ composites, there are no apparent differences observed between CeO₂ and mCeO₂ on improving the UV resistance of PC.     

Study of quasi-solid electrolyte in dye-sensitized solar cells using surfactant as pore-forming materials in TiO<Subscript>2</Subscript> photoelectrodes

A novel polymer gel electrolyte was used to improve the performance and long-term stability in dye-sensitized solar cells (DSSCs). The polymer gel electrolyte (PGE) was prepared by mixing 5 wt% poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and 2 % TiO₂ nanoparticles. The conductivity of PGE with P25 reached 9.98 × 10^?3 S/cm, which increased by 34.9 % compared with 7.40 × 10^?3 S/cm of PGE without P25, and the diffusion coefficient was also increased by 19.0 %. Different photoelectrodes were obtained by using three kinds of surfactants (cetylamine, octadecylamine, and P123) as pore-forming materials, and their morphologies were contrasted through scanning electron microscopy (SEM). The results showed that gel electrolyte can increase the short-circuit current density (J _sc) from 11.01 to 12.99 mA/cm² in DSSCs. Moreover, unlike the liquid electrolyte, the gel electrolyte is more conducive to the TiO₂ photoelectrodes with larger pores. In conclusion, the efficiency of DSSC with gel electrolyte and P123 as pore-forming material was 6.73 %, which was 12 % higher than the liquid electrolyte in the same test condition. In addition, the sealed gel electrolyte DSSCs showed better stability than did liquid electrolyte DSSCs during nearly 600 h.