Effect of ZnO nanoparticles doping on structural,dielectric and interfacial behavior of polyoxyethylene (20) sorbitan/ethylene glycol lyotropic phases

ABSTRACT

We are reporting on the interaction of zinc oxide (ZnO) nanoparticles (NPs) with the lyotropic phase comprises of Polyoxyethylene (20) sorbitan monolaurate and protic solvent ethylene glycol. The concentration of the NPs has been varying from 0.05 to 0.5 wt%. Multiwall lamellar and inverse phases have been observed at lower and higher concentration of ZnO NPs doping. Interestingly, the organization of ZnO NPs on the periphery and inside the periphery of ring-like structures has been observed at lower and higher concentration of the dopant, respectively. Such organization of the NPs can be explained considering interfacial interaction amid host and dopant and may also attribute to the adsorption mechanisms of surfactant. Effects of NPs doping on the dielectric dynamics has also been examined. About 32.6% decrease in the dielectric permittivity has been noticed at higher NPs doping. Such decrement in permittivity could be a result of the screening of the ZnO NPs dipole moment by the adsorption of surfactant molecules on their surface. Relaxation and optical parameters of the non-doped and doped mixtures have also been discussed.     

Investigation of dielectric and electro-optical properties of nematic liquid crystal with the suspension of biowaste-based porous carbon nanoparticles

ABSTRACT

The effect of biowaste porous carbon nanoparticles (PCNPs) on the dielectric and electro-optical properties of nematic liquid crystal (LC) mixture (1823A) of 4-(4-alkyl-cyclohexyl) benzene isothiocyanates and 4-(4-alkyl-cyclohexyl) biphenyl isothiocyanates has been studied. The dielectric permittivity of nematic LC has been increased with the dispersion of carbon NPs. The dielectric anisotropy has been calculated and found to be decreased with the dispersion of PCNPs into the pure nematic LC. The response time and birefringence have been also observed with the variation of temperature, frequency as well as the concentrations of carbon NPs. After the dispersion of PCNPs achieved better birefringence and faster response in the dispersed system, which is the significant application in display devices. Threshold voltage splay elastic coefficient and rotational viscosity have been calculated for both pure and NPs dispersed nematic system. Its value is increased with the dispersion of NPs. Additionally, photoluminescence and figure of merit have investigated as a comparative study of nematic matrix as well the dispersed system. The experimental results have been found to have good agreement with the theoretical data of nematic LC. An effort has been made to explain these experimental results on the basis of interaction between nematic molecules and carbon NPs.     

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.     

Cd1-xZnxS/ZnS core/shell quantum dot ferroelectric liquid crystal composite system: analysis of faster optical response and lower operating voltage

Cd_1?xZn_xS/ZnS core/shell-structured quantum dot (QD)-doped ferroelectric liquid crystal (FLC) Felix 17/000 has been investigated in the present study. In the SmC* phase, the effect of QD on the dielectric and electro-optical properties of FLC has been studied as a function of dopant concentration. A substantial change in the different parameters like tilt angle, spontaneous polarisation, response time and relative permittivity has been observed for the composite system. Nearly two times faster response of the composite system with lower operating voltage is one of the promising results of the present study. The faster optical response along with the decreased value of spontaneous polarisation can be utilised in low power consumption liquid crystal displays.     

Role of doping and CuO segregation in improving the giant permittivity of CaCu3Ti4O12

The dopant role on the electric and dielectric properties of the perovskite-type CaCu₃Ti₄O₁₂ (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1-2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90<ε_r<180. Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07 eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76 eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.     

Enhanced electro-optical properties of a nematic liquid crystals in presence of BaTiO3 nanoparticles

Composites of nematic liquid crystals (NLCs) and ferroelectric barium titanate (BaTiO₃) nanoparticles (NPs) have been prepared. The alignments of NPs in the host medium have been demonstrated. Effect of NPs doping on various display parameters of NLCs, namely, threshold voltage, dielectric anisotropy and splay elastic constant has been studied using electro-optical and dielectric studies. The nematic ordering of host supports alignment of NPs parallel to the director which consequently improves electro-optical parameters in the composite system. The dielectric and electro-optic properties of LC–NPs composites have been discussed in frame of conventional theories of NLCs.     

The Primary Origin of Excellent Dielectric Properties of (Co,Nb) Co-Doped TiO2 Ceramics: Electron-Pinned Defect Dipoles vs. Internal Barrier Layer Capacitor Effect

(Co, Nb) co-doped rutile TiO₂ (CoNTO) nanoparticles with low dopant concentrations were prepared using a wet chemistry method. A pure rutile TiO₂ phase with a dense microstructure and homogeneous dispersion of the dopants was obtained. By co-doping rutile TiO₂ with 0.5 at.% (Co, Nb), a very high dielectric permittivity of ε′ ≈ 36,105 and a low loss tangent of tanδ ≈ 0.04 were achieved. The sample–electrode contact and resistive outer-surface layer (surface barrier layer capacitor) have a significant impact on the dielectric response in the CoNTO ceramics. The density functional theory calculation shows that the 2Co atoms are located near the oxygen vacancy, creating a triangle-shaped 2CoV_oTi complex defect. On the other hand, the substitution of TiO₂ with Nb atoms can form a diamond-shaped 2Nb2Ti complex defect. These two types of complex defects are far away from each other. Therefore, the electron-pinned defect dipoles cannot be considered the primary origins of the dielectric response in the CoNTO ceramics. Impedance spectroscopy shows that the CoNTO ceramics are electrically heterogeneous, comprised of insulating and semiconducting regions. Thus, the dielectric properties of the CoNTO ceramics are attributed to the interfacial polarization at the internal insulating layers with very high resistivity, giving rise to a low loss tangent.     

Fast response in TN liquid-crystal cells: effect of functionalised carbon nanotubes

The optical response time of a nematic liquid crystal (NLC) decreases due to incorporation of carbon nanotubes (CNTs) in the liquid-crystal host. Such reduction is believed to be due to an increase in the elastic constant of the nanotube-doped LC system. In this paper, we present the effect on optical response due to doping an NLC with octadecylamine functionalised single-walled carbon nanotubes (ODA-SWCNT) in a twisted alignment mode. The electro-optic switching amplitude of ODA-SWCNT nanocomposites of NLC decreases compared to pure NLC. A fast response time is observed with an increase in the concentration of ODA-SWCNT in NLC host. Additionally, optical response of pure NLC in a twisted nematic (TN) cell fabricated using mixtures of polyimide (PI) and ODA-SWCNT as an alignment layer is investigated. The optical response time decreased by ~75% in a TN cell fabricated with a mixture of PI and ODA-SWCNT compared to that of a TN cell prepared using a pure PI alignment layer. The presence of ODA-SWCNT in the alignment layer enhances the surface anchoring of the NLC molecules leading to an increase in the elastic constant and a decrease in the optical response time of NLC.     

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

The present work concerns with the investigation of the effect of dispersion of Silica (SiO₂) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO₂ NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO₂ NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation P_s and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions.     

Effect of functionalised silver nanoparticle on the elastic constants and ionic transport of a nematic liquid crystal

ABSTRACT

Addition of nanomaterial into pure nematic liquid crystals (NLCs) leads to improvement in the various physical properties of the liquid crystal (LC) host. Doping of nanomaterials affects the local molecular arrangement of the LC molecules. Here, we present the results of our investigation on the effect of functionalised silver nanoparticles (f-AgNPs) on the physical properties of the rod-shaped NLC, 4-trans-pentyl-cyclohexyl cyanobenzene (5PCH). The dielectric constant, threshold voltage, elastic constants, birefringence and conductivity measurements were performed on pure 5PCH and its f-AgNPs doped nanocomposites as a function of temperature in planar cell. The magnitude of dielectric anisotropy, elastic constants and birefringence in nanocomposites were enhanced with increasing concentration of f-AgNPs indicating enhancement of order parameter in the nematic medium. Threshold voltage decreases with increasing concentration of f-AgNPs. Both parallel and perpendicular components of conductivity decrease with increasing concentration of f-AgNPs due to the absorption of ion by the doped f-AgNPs. This observed decrease in conductivity in nanocomposites is further confirmed by calculating the ion transportation number and time of flight. The ion transport number i.e ionic contribution present in the LC cell was found to be 0.966 in pure 5PCH, whereas 0.830 in 0.5 wt% of f-AgNPs nanocomposite of 5PCH.     

Conducting polyaniline-rutile TiO2 nanocomposites for the development of high-k dielectric materials

Inorganic dielectrics encapsulated in an organic matrix are showing excellent promise as novel dielectric materials. In this work, firstly highly organized crystalline nanoparticles of rutile TiO₂ were synthesized by acid hydrolysis of titanium isopropoxide at room temperature. Then we developed a novel dielectric material consisting of highly organized rutile TiO₂/polyaniline (PAni) nanocomposites by in-situ chemical oxidative polymerization. The structural, morphological, conducting, and dielectric properties of the rutile TiO₂/PAni nanoparticles have been evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission emission microscopy (HR-TEM), four-point probe technique, CV (Capacitance versus Voltage), and Impedance analyzer. The nanocomposites show 70 times higher permittivity compared to rutile nanoparticles and much higher compared to anatase/PAni (ES) nanocomposites at 10 MHz. Large interfacial polarizations, nanostructure, and dopant levels are the key factors for the large dielectric constant of the nanocomposites. The rutile/PAni (ES) nanocomposites might see potential uses in super-capacitors, gate dielectric in transistors, and capacitive-type gas sensors.     

Influence of low concentration silver nanoparticles on the electrical and electro-optical parameters of nematic liquid crystals

Thermodynamical, optical, dielectric and electro-optical characterisation of nematic liquid crystals (LCs) and silver nanoparticle (NP) composites have been carried out. Transition temperatures of pure and composites systems have been measured. Thermodynamical studies suggest increase of clearing temperature of the composite material as compared to the pure material. Threshold voltage for switching from bright to dark state and splay elastic constant of the pure and composite materials have been determined. From frequency dependence of dielectric measurements, permittivity, loss, relaxation frequency and dielectric strength of flip-flop mechanism of LC molecules in the nematic phase have been calculated. Dielectric properties of composites have been explained in reference of Maier and Meier theory. The effects of doping of NPs on dielectric and electro-optic properties of LC-NP composites have been discussed.     

Dielectric and visco-elastic properties of laterally fluorinated liquid crystal single compounds and their mixture

The physical properties of three laterally fluorinated liquid crystalline compounds with negative dielectric anisotropy have been studied from static dielectric permittivity, optical birefringence, bend elastic constant, relaxation time and rotational viscosity measurements. Such negative dielectric anisotropy materials find use as components of mixtures for application in vertically aligned mode liquid crystal displays. Moreover, the physical properties of one phenyl cyclohexane compound with positive dielectric anisotropy have also been studied. A five-component mixture comprising these four mesogens and a non-mesogenic component has been formulated and its physical properties have been thoroughly investigated. An attempt has been made to strike a balance between the optical birefringence of the mixture to adjust the cell gap and the dielectric anisotropy and threshold voltage (V_th ) to ensure low driving voltages. The pretilt angle effect on the threshold voltage and the relaxation time has also been studied. At T?=?20°C, the response time decreases to 22% and 41% for the mixture for 2° and 5° pretilt as compared to zero pretilt. On the other hand, at the same temperature the V_th values are decreased by 5% and 9%, respectively.     

Orientational instability of nematic liquid crystal in a homeotropic cell with boundary conditions controlled by an electric field

We study the orientational instability of the director in a homeotropic nematic liquid crystal (NLC) cell in a DC electric field. The electric field is applied along or perpendicular to a cell surface depending on whether anisotropy of dielectric permittivity of NLC is positive or negative. The easy axis on one of the cell polymer substrates is allowed to deviate in perpendicular to the substrate plane due to the influence of the NLC and the electric field. It was established that the orientational instability of the director can have a threshold as well as be thresholdless which depends on the character of the coupling of the easy axis with the electric field. The temporal behaviour of a director and the easy axis during transition to the stationary state after turning on electric field and returning to the initial homogeneous state after turning off the field was investigated. In the case of the negative anisotropy of the static permittivity, the comparison of experimental and calculated time dependences of the easy axis reorientation angle let us to estimate values of the mobile easy axis viscosity coefficient and coupling parameter describing the coupling between the easy axis and the electric field.     

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate in dioxane-water mixtures

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate, i-Pen ₄ NNO ₃ . in various dioxane-water mixtures have been studied using dielectric time domain spectroscopy (TDS). The static permittivity of the solutions _s increases for low concentrations of solute but levels off to asymptotic values at higher concentrations. The limiting sloped_s dc, and the asymptotic value depend on the static permittivity of the solvent mixture. The relaxation time due to the solute varies with solute concentration and depends on the solvent mixture. In the solvent mixtures of lowest permittivity the plots of relaxation time vs. concentration go through a maximum, while in the mixtures of highest permittivity the relaxation time initially decreases and then levels off to an asymptotic value. The concentration dependence of the dielectric parameters is discussed in relation to ion association.     

Electrochemical characterization of sodium and potassium doped lanthanum–titanium mixed oxides prepared by sol–gel method

Varying amounts of Na and K doped lanthanum–titanium oxides were synthesized by gel entrapment technique. These ceramics were characterized by X-ray diffraction. Microstructural investigations revealed grain growth in the doped material compared to undoped sample. Dielectric relaxations of these compounds were investigated in the temperature range 250–900 °C. A high degree of dispersion of the permittivity of un-doped lanthanum–titanium oxide and K and Na doped lanthanum–titanium oxide was observed in the frequency range <100 kHz which was attributed to oxygen vacancies. An increase in the permittivity values were observed with 1 % Na and K doped samples. The permittivity values further deteriorated with the dopant concentration. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The dielectric loss was found to decrease by doping K in lanthanum–titanium oxide matrix. The dc conductivity studies showed that a temperature dependent hopping type mechanism is responsible for electrical conduction in the system.     

Electrical and electro-optical parameters of 4ʹ-octyl-4-cyanobiphenyl nematic liquid crystal dispersed with gold and silver nanoparticles

Thermodynamical, dielectric, optical and electro-optical characterisation of pure 8CB and its composites with gold and silver nanoparticles have been studied. Thermodynamical studies suggest a decrease in clearing temperature of the nanocomposite systems as compared to the pure system. Dielectric parameters of pure nematic liquid crystal and nanocomposites in the homeotropic and planar aligned samples have been measured in the frequency range of 1–35 MHz. Ionic conductivity increases significantly in nematic and smectic A_d (SmA_d) phases, whereas dielectric anisotropy is almost unchanged for both the nanocomposites. Threshold voltage for Freederick transition, switching voltage and splay elastic constant have decreased in the case of nanocomposite systems. Relaxation frequency and activation energy of an observed relaxation mode corresponding to molecular rotation about the short axis increase in the SmA_d phases of both the nanocomposites. The optical study suggests that due to dispersion of nanoparticles, the optical band gap has decreased.     

Electronic band structure and optical properties of titanium oxyphosphates Li0.50Co0.25TiO(PO4) single crystals: An ab-initio calculations

From the refined atomic positions obtained by Belmal et al. (2004) [1] using X-ray diffraction for Li_0.50Co_0.25TiO(PO₄), we have performed a structural optimization by minimizing the forces acting on the atoms keeping the lattice parameters fixed at the experimental values. With this relaxed (optimized) geometry we have performed a comprehensive theoretical study of electronic properties and dispersion of the linear optical susceptibilities using the full potential linear augmented plane wave (FP-LAPW) method. The generalized gradient approximation (GGA) exchange-correlation potential was applied. In addition, the Engel-Vosko generalized gradient approximation (EVGGA) was used for comparison with GGA because it is known that EVGGA approach yields better band splitting compared to the GGA. We have calculated the band structure, and the total and partial densities of states. The electron charge densities and the bonding properties were analyzed and discussed. The complex dielectric optical susceptibilities were discussed in detail.     

Application of CuO nanoparticles modified with vitamin B1 for the production of poly(vinyl alcohol)/CuO nanocomposite films with enhanced optical,thermal and mechanical properties

In this Investigation, the CuO nanoparticles (NPs) were treated by vitamin B₁ as a biomolecule modifier. The CuO NPs were used as an appropriate filler for fabrication of poly(vinyl alcohol) (PVA) nanocomposites (NCs). Then, NCs with various ratios (3, 5, and 7wt%) of modified CuO were fabricated under ultrasonic irradiation and their properties were compared with pure PVA. Several techniques were used for characterization of NCs. Field emission scanning electron microscopy and transmission electron microscopy analysis indicated that NPs have proper compatibility with the PVA matrix. Thermal gravimetric analysis results confirmed that NCs displayed higher thermal stability than neat PVA. Also, the addition of the NPs into the PVA matrix improved the optical and mechanical behaviors. Finally, the contact angle measurements verified that the hydrophilicity decreased for different ratios of modified NPs loaded in the polymer matrix. Copyright © 2017 John Wiley & Sons, Ltd.