Aspect Ratio Of Nanoparticles Research Articles

Effects of interphase regions and tunneling distance on the electrical conductivity of polymer carbon nanotubes nanocomposites

In this paper, an analytical model is developed for electrical conductivity of nanocomposites, particularly polymer/carbon nanotubes nanocomposites. This model considers the effects of aspect ratio, concentration, waviness, conductivity and percolation threshold of nanoparticles, interphase thickness, wettability between polymer and filler, tunneling distance between nanoparticles and network fraction on the conductivity. The developed model is confirmed by experimental results and parametric studies. The calculations show good agreement with the experimental data of different samples. The concentration and aspect ratio of nanoparticles directly control the conductivity. Moreover, a smaller distance between nanoparticles increases the conductivity based on the tunneling mechanism. A thick interphase also causes an increased conductivity, because the interphase regions participate in the networks and enhance the effectiveness of nanoparticles.

Indium silicon oxide thin films for infrared metaphotonics

We demonstrate silicon-doped indium oxide (ISO) with tunable epsilon near-zero and plasmonic behavior and propose it as a Si-compatible alternative material for metaphotonic applications in the mid-infrared (MIR) spectral range. ISO thin films were grown using DC and RF magnetron cosputtering deposition. Post-deposition thermal annealing was performed that resulted in large tunability of the optical dispersion data, as measured directly by variable-angle ellipsometry. Screened plasma wavelengths in the range 1.7 μm–5.8 μm were experimentally obtained depending on the annealing conditions. Moreover, ISO films with 350 nm thickness were investigated by atomic force microscopy that reveals a maximum rms roughness of 1.9 nm, enabling high-quality nanofabrication. In order to demonstrate the suitability of ISO thin films for the fabrication of plasmonic structures, we have produced ISO nanoparticle disk arrays using electron-beam lithography on Al2O3 substrates and shown, using both finite element method simulations and Fourier transform infrared spectroscopy, distinctive plasmonic resonances at MIR wavelengths tuned by the nanoparticles' spacing and aspect ratio. A figure of merit based on Mie theory is computed for spheres whose radii are either λ/10 or λ/3 over a broad spectral range that enables quantitative comparison with alternative plasmonic materials and reveals the full potential of ISO for engineering localized surface plasmons across the MIR spectral range. The development of fully Si-compatible plasmonic materials with engineered optical dispersion is important to enable cost-effective photonic-plasmonic high-density device integration for metaphotonic research.

Exclusion and Trapping of Carbon Nanostructures in Nonisotropic Suspensions of Cellulose Nanostructures.

Incorporation of carbon nanotubes (CNTs) into liquid crystalline phases of cellulose nanocrystals (CNCs) may be used for preparation of hybrids with novel optical, electrical, and mechanical properties. Here, we investigated the effect of nanoparticle diameter, geometry, aspect ratio, and flexibility on the exclusion of dispersed carbon nanostructures (CNs) from the chiral nematic phase (N*) of the CNCs. Although the CNs are nicely dispersed in isotropic suspensions of CNCs, we observe that fullerenes, carbon black, and CNTs are depleted from the N* phase. This observation is surprising as theoretical predictions and previous observations of nanoparticles indicate that nanometric inclusions would be incorporated within the N* phase. Cryogenic transmission electron microscopy imaging reveals that the dispersed CNs induce misorientation of the CNCs, irrespective of their geometry and size. Rheological measurements suggest that about 10% of the CNCs are affected by the CNs. The multiparticle nature of the interaction may be the origin of the nonsize selective exclusion of the CNs. Re-entrant behavior is observed at high CNC concentrations (about 13 wt %), where a (nematic) gel-like phase kinetically traps the CNs. These phases exhibit non-Newtonian flow behavior and birefringence, offering a pathway for preparation of nonisotropic CNCs-CNT composites and thin films via liquid processing.

Growth Kinetics and Sensing Features of Colloidal Silver Nanoplates

This paper presents the growth mechanisms and the plasmon sensing features for a large class of silver nanoplates obtained in the colloidal form. The synthesis is conducted by seed-mediated growth and leads to plates with aspect ratios as large as 20, having localized surface plasmon resonances extending deeply into the infrared spectral region (1000 nm and above). We measure plasmon sensitivity by varying the colloidal local refractive index, and Δλ/Δn sensitivity values up to 500 nm/RIU are obtained. Theoretical considerations regarding the correlation between the refractive index sensitivity and the position of the main localized plasmon resonance band demonstrate that plasmon sensitivity does not depend directly on the nanoparticle shape and aspect ratio.

Physicochemical parameters - hydration performance relationship of the new endodontic cement MTA Repair HP.

BackgroundTo characterize the chemical composition and textural parameters of the MTA Repair HP precursor powder and their influence to hydration performance.Material and MethodsUn-hydrated precursor material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), laser diffraction (LD), N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated material was analysed by XRD, FT-IR, energy dispersive X-ray (EDX) analysis and FEG-SEM.ResultsCa3SiO5 and Ca2SiO4, in addition to CaWO4 as radiopacifier are the main compositional phases. Other measured parameter indicates high specific surface area of 4.8 m2 g-1, high aluminium content of 1.7 wt.% and low initial and final setting times of 12 and 199 min, respectively. Singular microstructural features consisting of high aspect ratio nanoparticles are main constituents of un-hydrated precursor. Besides, FEM-SEM observation shows notably growth of hexagonal shaped plate-like morphologies homogeneously distributed along the sample during hydration process.ConclusionsThe short setting time measured for HP Repair, is correlated with high surface area of precursor powder, high Al content and the absence of compositional sulphate phases. Key words:Bioactive endodontic cements, hydration performance, MTA HP Repair, physicochemical parameters.

Numerical study of MHD nanofluid natural convection in a baffled U-shaped enclosure

In this study, nanofluid natural convection in a baffled U-shaped enclosure in the presence of a magnetic field is investigated. Lattice Boltzmann method (LBM) is used to study present problems. KKL (Koo-Kleinstreuer-Li) correlation is applied to calculate the effective thermal conductivity and viscosity of nanofluid. The effect of the Brownian motion on the effective thermal conductivity is considered in this correlation. The combination of the four topics (nanofluid, U-shaped enclosure, baffle, magnetic field) is the main novelty of the present study. Effect of Rayleigh number, Hartmann number, nanoparticle volume fraction and cavity aspect ratio on the flow field and heat transfer characteristics have been investigated. The results demonstrate that the average Nusselt number increases by increments of the Rayleigh number, nanoparticle solid volume fraction and aspect ratio. However, the rate of heat transfer is suppressed by the magnetic field. The effect of magnetic field on heat transfer is more significant at higher Rayleigh number and the effect of Ra on the average Nusselt number is more noteworthy at lower Ha. Besides, the effect of Rayleigh number on heat transfer enhancement becomes more significant at higher aspect ratio.

The effect of filler geometry on thermo-optical and rheological properties of CuO nanofluid

In the present work, we investigate the effect of nanoparticle crystallite size and shape on the thermal, rheological and optical properties of low-cost copper oxide nanofluid. Nanofluids are prepared by suspending 0.3% volume of nanoparticles in the 70:30 ethylene glycol:distilled water mixture using ultrasonic vibration, and followed by the microwave irradiation. Our results indicate that the zeta potential values of the nanofluids decrease as nanoparticle anisotropy or aspect ratio increases, zeta potential values decreases. Moreover, the increase in the thermal conductivity of the nanofluids is maximum for the nanofluids prepared using nanorods having the highest aspect ratio of 5.84. The rheology data of the CuO nanofluids with different shapes of nanoparticles at a particle volume fraction of 0.3% indicates that the nanofluids predominantly show Newtonian behaviour, exemplified by the shear rate independent viscosity. Moreover, the rheological behaviour is observed to depend on crystallite size and the nanoparticles shape as marked by an increase in the viscosity which follows the order, spherical < cubelike < rectangular < nanobar < nanorods. The comparison of the optical transmittance spectra for the base fluid and CuO suspended nanofluids suggests that the latter have higher adsorption capacity than the base fluid in the range 940 and 1165 nm. The CuO nanofluids with different shapes can be potentially utilised as direct solar absorber and heat transfer fluid and also as a coolant owing to their excellent stability, high thermal conductivity and low viscosity.

Rheological analysis of MWCNT, TiO2, CuO based Nano—Fluids under varying temperatures and concentrations

The present work aims to determine the effect of Nanoparticles in Water - Ethylene glycol mixture on contradictory results in literature, which includes thermo-physical property focusing on viscosity. The experimental analysis was carried out using Rheometer on Water - Ethylene glycol based Nano fluid containing 0.015 % and 0.15 % by weight concentration of cylindrical MWCNT, spherical CuO and TiO2 at 10 °C, 20 °C, 30 °C and 40 °C. The Rheometer procured result of viscosity shows that the Newtonian to shear thinning transition takes place at high shear stress range in comparison to the base fluid. At 10 °C, highest increment in the viscosity was noted by MWCNT (0.015 % by mass) over (0.15 % by mass) for CuO, 139.3 % increment and TiO2 recorded 64.73 % for (0.015 % by mass) over (0.15 % by mass). Moreover, the modified Maron and Pierce model predicted the viscosity of Nano-Fluid which in turn resulted in showing that viscosity ration of Nano-Fluid increased with increase in temperature due to the addition of high surface activity Nano particles into water-ethylene glycol mixture. The aspect ratio, Brownian motion, shear thinning and surface activity of Nano particles played a major role in the viscosity analysis.

Shape memory polyurethane nanocomposites with porous architectures for enhanced microwave shielding

Thermoplastic Polyurethanes (TPU) are versatile smart materials exhibiting shape memory property and have wide usage in the field of microwave shielding through incorporation of microwave active nanoparticles. The incorporation of high aspect ratio particles into the shape memory polymer matrix may however lead to increase in stiffness and thereby loss of shape memory property. To successfully incorporate high aspect ratio nanoparticles in the polymer matrix, porous polyurethane membranes were prepared by phase inversion technique using polyethylene glycol (PEG) as pore forming agent. The pore sizes were tuned to be of the order of 1–3 µm in size by varying the PEG concentration in the dope solution to facilitate the vacuum filtration of an aqueous nanoparticles solution through the porous structure. This technique helped to preserve the shape memory property of PU which would otherwise be disturbed if nanoparticles were incorporated into the polymer matrix. From the results obtained it was clear that this strategy of coating nanoparticles onto the porous membranes helped in achieving good shielding effectiveness at relatively lower membrane thickness without compromising much on the shape memory property of the membranes which otherwise is impeded at higher filler content. When stacked to form a sandwich structure of about 400 µm thickness, the membranes showed a high shielding effectiveness of −32 dB manifesting in 99.9% attenuation of electromagnetic radiations.

Effects of Magnetohydrodynamics on Natural Convection and Entropy Generation with Nanofluids

The paper presents a numerical study of the magnetohydrodynamic natural convection heat transfer of a heated block situated on the bottom wall of an enclosure filled with nanofluids. The transport equations for a Newtonian fluid are solved numerically using the lattice-Boltzmann method. The effective thermal conductivity and viscosity of the nanofluid are calculated by the Koo–Kleinstreuer–Li correlation. The influence of pertinent parameters such as Rayleigh number, solid volume fraction, Hartmann number, magnetic field inclination angle, nanoparticle volume concentration and aspect ratio of the rectangular heated block on the flow, heat transfer characteristics, and entropy generation has been investigated. It is found that the total entropy generation is an increasing function of the Rayleigh number, whereas it is a decreasing function of the Hartmann number. Moreover, the numerical results demonstrate that the average Nusselt number increases steadily but nonlinearly by the augmentation of the nanoparticle volume fraction. Also, the results show that the magnetic field with an inclination angle of has the maximum heat transfer coefficient and total entropy generation.

Properties of polycrystalline nanoparticles with uniaxial and cubic types of magnetic anisotropy of individual grains

The influence of the crystal structure inhomogeneities on the magnetic properties of cobalt nanoparticles with different aspect ratio and spherical nanoparticles of chromium dioxide, cobalt ferrite and magnetite has been studied by means of numerical simulation. The polycrystalline nanoparticles are modeled by means of subdivision of the nanoparticle volume into tightly bound single-crystal granules with randomly distributed directions of the easy anisotropy axes. The probability of appearance of quasi uniform and vortex states in sufficiently large assemblies of polycrystalline nanoparticles of various types have been calculated depending on the nanoparticle diameter. It is shown that the subdivision of a nanoparticle into single-crystal granules with different orientations of the easy anisotropy axes substantially reduces the effective single-domain diameters for particles with uniaxial type of anisotropy of individual granules. However, for particles with cubic type of magnetic anisotropy the influence of the crystal structure inhomogeneities on the equilibrium properties of the particles is not so important even for magnetically hard cobalt ferrite nanoparticles. It is practically absent for magnetically soft magnetite nanoparticles.

Optimizing experimental conditions in synthesizing WO3 nanopowders through sol-gel method using Taguchi design

In this research, the Taguchi method with L9 orthogonal array was applied to optimize the experimental parameters used in synthesizing tungsten trioxide, WO3, nanopowders through the simple, fast, and cost-effective sol-gel method. Synthesis parameters, including sodium tungstate and acid concentrations, sodium tungstate to oxalic acid, and sodium tungstate to cetyltrimethylammonium bromide weight ratios were considered as the Taguchi factors. The average size and aspect ratio of WO3 nanoparticles were considered as the characteristic factors. The optimum condition for these factors was introduced using the signal-to-noise ratio analysis. The condition was obtained as follows: sodium tungstate concentration of 0.25 mol/l, acid concentration of 1 mol/l, sodium tungstate to oxalic acid weight ratio of 1:2, and sodium tungstate to cetyltrimethylammonium bromide weight ratio of 1:0.4 for the average particle size; sodium tungstate and acid concentrations of 1 and 3 mol/l, respectively; and sodium tungstate to oxalic acid and sodium tungstate to cetyltrimethylammonium bromide weight ratios of 1:1.5 and 1:0.4, respectively, for the aspect ratio. The concentration of sodium tungstate and its weight ratio to cetyltrimethylammonium bromide were proposed as the main parameters influencing the size and aspect ratio of WO3 nanopowders. Also, under the optimum condition, WO3 nanopowders were prepared, and their structure, as well as chemical composition, were characterized using field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Characterizing the final product synthesized under the optimum condition confirmed producing the nanopowder with an average particle size of 47 nm and aspect ratio of 1.22.

Percolating Behavior of Nanoparticles in Block Copolymer Host: Hybrid Particle-Field Simulations

The hybrid particle–field method is extended to investigate self-assembly and percolating behavior of nanocomposites containing block copolymers and nanoparticles. The self-assembled nanostructures serve as templates to guide organization and distribution of nanoparticles. The percolation threshold of nanoparticles in the host of block copolymers is discussed in terms of composition of block copolymers, radius, and aspect ratio of nanoparticles. The simulated results demonstrate that the block copolymers have a synergistic or antagonistic effect on emergence of percolating network of nanoparticles, depending on the copolymer composition. There exists an optimal value of copolymer composition for lowering the percolation threshold of nanoparticles. In addition, regulating the geometrical shape of nanoparticles further lowers the percolation threshold of nanoparticles dispersed in the block copolymers. These simulated results provide useful guidelines for designing high-performance composite materials with ...

Magneto-actuated cell apoptosis by biaxial pulsed magnetic field

We report on a highly efficient magneto-actuated cancer cell apoptosis method using a biaxial pulsed magnetic field configuration, which maximizes the induced magnetic torque. The light transmissivity dynamics show that the biaxial magnetic field configuration can actuate the magnetic nanoparticles with higher responsiveness over a wide range of frequencies as compared to uniaxial field configurations. Its efficacy was demonstrated in in vitro cell destruction experiments with a greater reduction in cell viability. Magnetic nanoparticles with high aspect ratios were also found to form a triple vortex magnetization at remanence which increases its low field susceptibility. This translates to a larger magneto-mechanical actuated force at low fields and 12% higher efficacy in cell death as compared to low aspect ratio nanoparticles.

Highly Concentrated Seed-Mediated Synthesis of Monodispersed Gold Nanorods

The extremely large optical extinction coefficient of gold nanorods (Au-NRs) enables their use in a diverse array of technologies, rnging from plasmonic imaging, therapeutics and sensors, to large area coatings, filters, and optical attenuators. Development of the latter technologies has been hindered by the lack of cost-effective, large volume production. This is due in part to the low reactant concentration required for symmetry breaking in conventional seed-mediated synthesis. Direct scale up of laboratory procedures has limited viability because of excessive solvent volume, exhaustive postsynthesis purification processes, and the generation of large amounts of waste (e.g., hexadecyltrimethylammonium bromide(CTAB)). Following recent insights into the growth mechanism of Au-NRs and the role of seed development, we modify the classic seed-mediated synthesis via temporal control of seed and reactant concentration to demonstrate production of Au-NRs at more than 100-times the conventional concentration, while maintaining independent control and narrow distribution of nanoparticle dimensions, aspect ratio, and volume. Thus, gram scale synthesis of Au-NRs with prescribed aspect ratio and volume is feasible in a 100 mL reactor with 1/100th of organic waste relative to conventional approaches. Such scale-up techniques are crucial to cost-effectively meet the increased demand for large quantities of Au-NRs in emerging applications.

Nanolubricants flow boiling heat transfer enhancement in a microfin tube evaporator—IRG0021

The current article experimentally documents the effects of the nanoparticles thermal conductivity and aspect ratio on the two-phase flow heat transfer coefficient and pressure drop of nanolubricants in mixture with refrigerant R410A. Two nanoparticles types were dispersed in the polyolester lubricant: spherical Alumina (γ-Al2O3) nanoparticles with 40 nm nominal particles diameter and ZnO nanoparticles with 20 to 40 nm nominal particles diameter and with an elongated shape. While the two nanolubricants had different nanoparticle aspect ratio, they shared similar thermal conductivity. In refrigerant R410A and polyolester mixtures, they led to measurably different heat transfer coefficient for two-phase flow boiling inside a horizontal 9.5 mm micro-fin evaporator tube. Depending on mass flux, concentration, and heat flux, nanolubricants provided either an enhancement or a degradation, supporting the hypothesis that the nanolubricants thermal conductivity was not the main property responsible for the heat transfer coefficient intensification during flow boiling. The current article presents an analysis of the nanolubricants heat transfer models that adopted homogeneous liquid phase modeling approaches during the two-phase flow process. A sensitivity analysis of the thermodynamic properties highlighted that these type of models were not able to satisfactorily predict the heat transfer coefficient and pressure drop of refrigerant-nanolubricants mixtures.

Slow and Stopped Light in Active Gain Composite Materials of Metal Nanoparticles: Ultralarge Group Index‐Bandwidth Product Predicted

Chip‐compatible slow light devices with large group index‐bandwidth products and low losses are of great interest in the community of modern photonics. In this work, active gain materials containing metal nanoparticles are proposed as the slow and stopped light materials. Gain‐assisted high field enhancement in metal nanoparticles and the resultant strong dispersion lead to such phenomena. From the Maxwell‐Garnett model, it is revealed that the metal nanocomposite exhibits the infinitely large group index when the gain of the host medium and the filling factor of metal nanoparticles satisfy a critical condition. For the gain of the host above the critical value, one can observe slowing down effect with amplification of light pulses. Significantly large group index‐bandwidth products, which vary from a few to several thousand or even infinity depending on the gain value of the host medium, have been numerically predicted in active silica glasses containing spheroidal metal nanoparticles, as examples. The proposed scheme inherently provides the widely varying operating spectral range by changing the aspect ratio of metal nanoparticles and chip‐compatibility with low cost.

Investigation of volume fraction of nanoparticles effect and aspect ratio of the twisted tape in the tube

In present study, the heat transfer of laminar and turbulent flow of water/Al2O3 nanofluid in the volume fraction of φ = 0–4% of solid nanoparticles in Reynolds numbers of 500–25,000 have been numerically investigated. The studied geometrics is a three-dimensional tube with the diameter of D = 2 cm and the length of L = 50 cm. In order to increase the heat transfer inside horizontal tube, the twisted tape in different aspect ratios has been used. In this research, the considered geometrics with aspect parameters, such as the twisted ratios (P/W) of 3, 3.5 and 4, the space ratios (C/D) of 0.3, 0.4 and 0.5 and the tape width ratios (W/D) at the range of 0.5–0.9, has been investigated. The results indicate that, in the turbulent flow, the use of solid nanoparticle in higher volume fractions and Reynolds numbers, comparing to the laminar flow, improves heat transfer. The existence of solid nanoparticles in lower twisted ratios (P/W) has great effect on the heat transfer enhancement. In the laminar flow, by increasing the width of twisted tape and the concentration of nanoparticles, heat transfer enhances.

Plasmonic ZnO/p-silicon heterojunction solar cell

A ZnO/p-Si heterojunction solar cell has been fabricated by sol-gel technique. Silver nanostructures have been deposited on the top surface of the cell by pulsed laser deposition (PLD) system. Silver nanoparticles show strong surface plasmon resonance at 500 nm and improve the overall absorbance of the cell. Deposition of silver nanoparticles on the top surface of the solar cell quenches the photoluminescence and indicates an effective scattering of incident light into the absorber layer. A solar cell containing silver nanoparticles shows fivefold improvement in short circuit current density in comparison to a pristine cell. Finite-difference time-domain (FDTD) simulations illustrate the effect of silver nanoparticles on the performance of the solar cell. The total quantum efficiency (TQE) of the device shows a Gaussian curve with the aspect ratio (diameter: interspacing) of nanoparticles. Optimized distribution of silver nanoparticles can improve the light trapping capabilities of various thin-film solar cells.

The mechanical behavior of CNT reinforced nanocomposites assuming imperfect interfacial bonding between matrix and nanoparticles and percolation of interphase regions

The effective inverse aspect ratio (αeff) and volume fraction (φeff) of nanoparticles in polymer/CNT nanocomposites are defined accounting imperfect interfacial adhesion between polymer matrix and nanoparticles and percolation of interfacial regions as interphase percolation. After that, the tensile modulus and strength of nanocomposites are expressed by Halpin-Tsai and Pukanszky models to show the effects of radius (R) and length (l) of nanoparticles as well as the interphase thickness (t) and interfacial shear strength (τ) on the mechanical properties of nanocomposites. The best levels of “αeff” and “φeff” are obtained by the thinnest and the longest nanotubes as well as the highest values of “t” and “τ” factors. The best relative modulus of 8 is calculated by R < 13 nm and l > 6500 nm, while the strength slightly improves by R < 17 nm. Likewise, the relative modulus of 9 is calculated at t > 20 nm and τ > 170 MPa, while the best relative strength of 4.5 is shown at the highest levels of t = 25 nm and τ = 300 MPa. Conclusively, the interphase properties further affect the mechanical properties of nanocomposites compared to material parameters.