SYNTHESIS AND CHARACTERIZATION OF (ZNO)–(CO3O4) NANOCOMPOSITE VIA SPRAY PYROLYSIS PROCESS: THE USE OF THE BRUGGEMAN MODEL ON OPTICAL PROPERTIES PREVISION

In the present paper, (ZnO)–(Co3O4) nanocomposite thin films have been prepared by using spray pyrolysis deposition on a glass substrate at 350∘C. After that, the as-obtained films have been characterized and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the double beam UV-visible (UV-vis) spectrophotometer. Furthermore, the Bruggeman model is used to predict the evolution of the optical dielectric constant (real and imaginary parts: [Formula: see text] and [Formula: see text] to compare them with those obtained from the experimental results. The XRD pattern reveals that the nanocomposite film has diffraction peaks 2[Formula: see text], 36.95∘ corresponding respectively to the (220), (311) planes of cubic Co3O4 and another about of 2[Formula: see text] corresponding to the (101) plane of Wurtzite ZnO. Using the Debye Scherrer formula, the crystallite size of (ZnO)[Formula: see text]–(Co3O[Formula: see text] nanocomposite is found about 32[Formula: see text]nm, while the obtained thickness of this nanocomposite is about 780[Formula: see text]nm using the DekTak Stylus profilometer. Besides, the morphology analysis shows that the nanocomposite sample is well covered without holes and/or cracks and it has uniform dense grains. The evaluation of the transmittance, reflectance, refraction index, extinction coefficient, real and imaginary parts of dielectric constant as function of wavelength illustrates that the optical response of nanocomposite thin film (ZnO)[Formula: see text]–(Co3O[Formula: see text] depends on the influence of two mediums of pure materials ZnO and Co3O4 and their interaction. In addition, the direct band gap vs incident photon energy obtained from the Tauc plot equation shows that this nanocomposite has three values of band gap energy which are [Formula: see text][Formula: see text]eV, [Formula: see text][Formula: see text]eV (correspond to pure Co3O4 film) and [Formula: see text][Formula: see text]eV (correspond to pure ZnO film). Besides, the application of the Bruggeman equation indicates that the influence of the values of volume concentration and optical dielectric constant of the ingredient nanomaterials (ZnO and Co3O[Formula: see text] is significant on the value of the effective dielectric constant of nanocomposite thin film. The specific result of this study is the similarity between the spectra obtained from the Bruggeman model and the measured one, which proves that the application of this model is useful for the prediction of the optical properties of the composite.

Effective Debye relaxation models for binary solutions of polar liquids at terahertz frequencies

Compared to the Bruggeman model, the proposed effective Debye models accurately predict the complex dielectric functions of alcohol–water mixtures. The improvements in the lower frequencies suggest that the calculations also describe the complex hydrogen-bond networks within the solutions.

Research of electromagnetic characteristics of planar chiral metastructures based on composite helices components taking into account the heterogeneous Bruggeman model

In this work a mathematical model of a chiral metamaterial is constructed which based on composite fine-wire helices components, which takes into account the properties of chirality, heterogeneity and dispersion. When constructing the model the chiral metamaterial was considered as a heterogeneous system and described by the Bruggeman model. Inthis work, analytical relationships were obtained for calculating the resonance frequencies of composite helices components. Thedispersion properties of the metamaterial were described using the well-known Condon model. As an example of using the constructed mathematical model, we solved the problem of the reflection (transmission) of a plane electromagnetic wave of linear polarization from a planar layer of the chiral structure under study based on composite helices microelements. A system of linear algebraic equations was obtained to determine the reflection and transmission coefficients of the main and cross-polarized field components. As a result of the numerical simulation, the frequency-selective properties of the metastructure were discovered and the frequencies at which the electromagnetic wave is captured by the planar layer of the metastructure were revealed. A similar effect can be used to creation of frequency selective concentrators (hubs) of microwave energy.

Nonlinear Thermal Radiation and Chemical Reaction Effects on a (Cu−CuO)/NaAlg Hybrid Nanofluid Flow Past a Stretching Curved Surface

The boundary layer flow of sodium alginate ( NaAlg ) based ( Cu − CuO ) hybrid nanofluid, over a curved expanding surface, has been investigated. Heat and mass transport phenomena have also been analyzed. Moreover, the impacts of chemical reaction, magnetic field and nonlinear thermal radiation are also a part of this study. This arrangement has great practical relevance, especially in the polymer and chemical industries. We have extended the Bruggeman model to make it capable of capturing the thermal conductivity of ( Cu − CuO ) / NaAlg hybrid nanofluid. We have employed some suitable transformations to obtain the governing system of nonlinear ODEs. Runge − Kutta − Fehlberg algorithm, accompanied by a shooting technique, has been employed to solve the governing system numerically. The changes in the flow and heat transfer distribution, due to various parameters, have been captured and portrayed in the form of graphs. It has been found that the addition of the nanometer-sized materials, significantly boosts the thermal and heat transport properties of the host fluid, and these phenomena seem to be more prominent, in the case of ( Cu − CuO ) / NaAlg hybrid nanofluid.

Dust Library of Plasmonically Enhanced Infrared Spectra of Individual Respirable Particles

This work characterizes collections of infrared spectra of individual dust particles of ∼4 µm size that were obtained from three very different environments: our lab air, a home air filter, and the 11 September 2001 World Trade Center event. Particle collection was done either directly from the air or by placing dust powder from various samples directly on the plasmonic mesh with 5 µm square holes as air is pumped through the mesh. This arrangement enables the recording of “scatter-free” infrared absorption spectra of individual particles of size comparable to the probing wavelengths whose vibrational signatures are otherwise dominated by scattering and dispersive line shape distortions. The spectra are sensitive to the amounts of various infrared active components and analysis using a Mie–Bruggeman model for mixed composition particles provides volume fractions of the components. Inhalation of dust particles of ∼4 µm size has significant health consequences as these are among the largest inhaled into people's lungs. The chemical composition of ∼4 µm respirable particles is of great interest from health, atmospheric, and environmental perspectives as different environments may pose different hazards and spectroscopic challenges.

Gas Permeation Models in Mixed Matrix Membranes for Gas Separation

Various theoretical models on CO2 permeation were discussed that included Maxwell model, Bruggeman model, Lewis-Nielson model and Pal model. These models were used for comparing the relative permeance of CO2 with the previously published experimental data on silica nanoparticles filled polysulfone/polyimide (PSF/PI) mixed matrix membranes (MMMs). The results showed that the deviation was in the increasing order: Lewis-Nielsen model< Maxwell model< Pal model< Bruggeman model. All these models assumed that the fillers are spherical in shape. A scanning electron microscope (SEM) cross-sectional image indicated that the silica particles were prolate ellipsoids that were dispersed in the matrix. To investigate the prolate effect, the Maxwell-Wagner-Sillar (MWS) model was employed. The evaluation from cross-sectional image of the membrane structure indicated that the shape factor along z-direction gave a minimum deviation of 17.52%-20.10% at 2-10 bar feed pressure respectively.

DIELECTRIC ANALYSIS ON OPTICAL PROPERTIES OF ZrO2 THIN FILMS DISPERSED WITH SILVER NANOPARTICLES

ZrO2 thin films containing silver nanoparticles were prepared using the sol-gel method with silver volume fractions from 5.3 to 53.9 %. An amorphous phase was observed for the ZrO2 matrix and a cubic crystalline phase was identified for the Ag nanoparticles by the XRD measurement. The diameter of silver nanoparticles distributed over 25 to 75 nm was analyzed by TEM measurement. The films showed an absorption band centered at 450 nm due to the surface plasmon resonance of silver nanoparticles. The absorption peak was analyzed using the effective dielectric function modeled with both Maxwell-Garnett and Bruggeman expressions. In the small Ag volume fractions, the calculated spectra using Maxwell-Garnett theory agreed well with the measured spectra. In the large Ag volume fraction, the calculated absorption spectra using the Bruggeman model gives a relatively good fitting to the experimental spectrum.