Aspect Ratio Of Nanoparticles Research Articles

FEM analysis of the stiffness evolution in clustered composites and nanocomposites

This work is aimed at studying the stiffness evolution of clustered composites and nanocomposites by FEM analysis. In fully dispersed composites and nanocomposites, proper modeling requires accounting for nanoparticle aspect ratio, volume fraction, and angle of orientation. In addition to these, the FEM model proposed in this work accounts for number of nanoparticles and volume fraction of nanoparticles in the cluster. The proposed approach allowed to calculate the longitudinal modulus and the other elastic constants of clustered composites, showing significant differences with the modulus of fully disperse composites.

Gas Permeation Model of Mixed-Matrix Membranes with Embedded Impermeable Cuboid Nanoparticles.

In the packaging industry, the barrier property of packaging materials is of paramount importance. The enhancement of barrier properties of materials can be achieved by adding impermeable nanoparticles into thin polymeric films, known as mixed-matrix membranes (MMMs). Three-dimensional numerical simulations were performed to study the barrier property of these MMMs and to estimate the effective membrane gas permeability. Results show that horizontally-aligned thin cuboid nanoparticles offer far superior barrier properties than spherical nanoparticles for an identical solid volume fraction. Maxwell’s model predicts very well the relative permeability of spherical and cubic nanoparticles over a wide range of the solid volume fraction. However, Maxwell’s model shows an increasingly poor prediction of the relative permeability of MMM as the aspect ratio of cuboid nanoparticles tends to zero or infinity. An artificial neural network (ANN) model was developed successfully to predict the relative permeability of MMMs as a function of the relative thickness and the relative projected area of the embedded nanoparticles. However, since an ANN model does not provide an explicit form of the relation of the relative permeability with the physical characteristics of the MMM, a new model based on multivariable regression analysis is introduced to represent the relative permeability in a MMM with impermeable cuboid nanoparticles. The new model possesses a simple explicit form and can predict, very well, the relative permeability over an extensive range of the solid volume fraction and aspect ratio, compared with many existing models.

Numerical simulation of nanoparticles size/aspect ratio effect on thermal conductivity of nanofluids using lattice Boltzmann method

Recent developments in nanofluids have led to a renewed interest in the geometrical effects of nanoparticles on the effective thermal conductivity (ETC) of nanofluids. Although the experimental data for the effect of nanoparticles shapes (the aspect ratio) on ETC are quite consistent, there are still controversial results regarding the effect of the nanoparticles size. Theoretical approaches have been proposed to shed light on the experimental observations in both macroscopic and microscopic scales. However, these approaches cannot be generalized due to the collective interrelated behaviours of nanoparticles. In this paper, a mesoscale numerical simulation, Lattice Boltzmann method (LBM), is implemented to study the effect of nanoparticle geometry on the nanofluids thermal conductivity. The results demonstrate that the nanofluids thermal conductivity and the nanoparticles volume fraction can be linearly correlated. In essence, increasing the nanoparticles aspect ratio can improve ETC of nanofluids. However, the nanoparticle size is not statistically significant (P-value>0.05) to be considered as an influencing parameter (as observed in the controversial results of the experiments) when the interfacial phenomena are not taken into account. The surface to volume ratio of the particle is the parameter that should be studied as all the solid/liquid interfacial interactions depends on this ratio.

Machine learning approach for elucidating and predicting the role of synthesis parameters on the shape and size of TiO2 nanoparticles

In the present work a series of design rules are developed in order to tune the morphology of TiO2 nanoparticles through hydrothermal process. Through a careful experimental design, the influence of relevant process parameters on the synthesis outcome are studied, reaching to the develop predictive models by using Machine Learning methods. The models, after the validation and training, are able to predict with high accuracy the synthesis outcome in terms of nanoparticle size, polydispersity and aspect ratio. Furthermore, they are implemented by reverse engineering approach to do the inverse process, i.e. obtain the optimal synthesis parameters given a specific product characteristic. For the first time, it is presented a synthesis method that allows continuous and precise control of NPs morphology with the possibility to tune the aspect ratio over a large range from 1.4 (perfect truncated bipyramids) to 6 (elongated nanoparticles) and the length from 20 to 140 nm.

Destabilization of the Nematic Phase of Clay Nanosheet Suspensions by Polymer Adsorption.

Complex aqueous mixtures comprised of swelling clays and hydrosoluble polymers naturally occur in soils and play a major role in pedogenesis. They are also very often used for formulating oil-well drilling fluids, paints, and personal-care products. The suspensions of some natural clays, thanks to their large nanoparticle aspect ratio, spontaneously form nematic liquid-crystalline phases where the particles align parallel to each other, which affects their flow properties. We observed that adding small amounts of hydrosoluble polymers to these clay suspensions destabilizes the nematic phase with respect to the isotropic (disordered) phase. The polymers that we used (poly(ethylene oxide) and dextran) were too small to adopt particle-bridging conformations and small-angle X-ray scattering experiments showed that the structure of the nematic phase is not altered by polymer doping. However, the adsorption isotherm shows that the macromolecules adsorb onto the clay nanosheets, effectively coating them with a polymer layer. Our extension of Onsager's theory for polymer-coated platelets properly captures the experimental phase diagram and shows how the nematic phase destabilization can be due to the polymer adsorbing more on the platelet faces than at the rim. Because the flow properties of the nematic phase are very different from those of the isotropic phase, the presence or absence of the former phase is an important factor to be determined and considered to explain the rheological behavior of these complex systems.

Production routes to tailor the performance of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are bio-based, high aspect ratio nanoparticles that are industrially produced in tonne-per-day quantities across the globe. CNCs can be used to improve the performance of a large range of materials such as emulsions and foams, biomedical devices, electronics and sensors, high-viscosity fluids and polymer composites. Their ability to do so, however, is highly dependent on the way they are produced. In this Review, we assess the properties of CNCs from more than 30 production routes and 40 biomass sources to help CNC users select the right material for their desired application. CNCs produced by various methods are evaluated against three target properties: colloidal stability, size and crystallinity index. Alternative production routes and/or starting materials are suggested to overcome challenges associated with CNC use, including increasing compatibility with hydrophobic materials, resistance to thermal degradation and colloidal stability in high ionic strength environments. Additionally, we discuss industrial production of CNCs, as well as considerations for increasing the yield and reducing the environmental impact of these processes. Overall, this Review guides researchers and CNC users towards a deeper understanding of how production processes can be modified to control CNC properties and subsequently tailor their performance. Cellulose nanocrystals are rigid rod-shaped nanoparticles that show promise as additives in composites, emulsions, foams and biomedical devices and as rheological modifiers. In this Review, the authors guide end users towards selecting cellulose sources and production routes that optimize the performance of cellulose nanocrystals in their intended application.

Nanocellulose-based products for sustainable applications-recent trends and possibilities

The bio-based products can provide a solution to the problems associated with petroleum shortages and waste treatment. Nanocellulose development has raised massive interest for a variety of applications pertinent to the material engineering to biomedical fields due to its biodegradable nature, impressive optical properties, anisotropic shape, high mechanical strength, excellent biocompatibility and tailorable surface chemistry. The nanocellulose composites show improved properties compared to other biopolymers due to their high surface area and large aspect ratio of nanoparticles. In this review, a clear overview of nanocellulose extraction, structural properties, sources and their applications in versatile fields are discussed. The foreseen markets of nanocellulose products can be categorised into different levels namely low-end, mid-range and high-end applications. An interdisciplinary research is essential to commercialize nanocellulose based products for sustainable applications.

Synthesis of early transition metal oxide nanomaterials and their conversion to nitrides

The synthesis of nanorods and nanowires of early transition metal oxides by hydrothermal methods and the conversion of some bulk oxides to nitrides in NH3 flow are both well established. However, the conversion of such oxide nanostructures to nitrides is not as well explored but could be a valuable method of producing nanowires, nanorods, and other asymmetric or high aspect ratio nanoparticles of the highly conductive metal nitrides. In this work, nanostructures of TiO2, V2O5, MoO3, and WO3 and mixtures thereof were synthesized by hydrothermal reactions, and conversion into nitride was attempted by heating the oxide material under NH3 flow with or without N2 flow. It was found that slow heating produces the best shape retention, but the nitridized products are porous in even the most favorable cases. The products were characterized by X-ray powder diffraction and scanning electron microscopy. Two-point conductivity measurements were done on the nitride materials, and optical measurements to characterize the plasmon absorption were done in favorable cases.

Facile decoding of quantitative signatures from magnetic nanowire arrays

Magnetic nanoparticles have been proposed as contact-free minimal-background nanobarcodes, and yet it has been difficult to rapidly and reliably decode them in an assembly. Here, high aspect ratio nanoparticles, or magnetic nanowires (MNWs), are characterized using first-order reversal curves (FORC) to investigate quantitative decoding. We have synthesized four types of nanowires (differing in diameter) that might be used for barcoding, and identified four possible “signature” functions that might be used to quickly distinguish them. To test this, we have measured the signatures of several combination samples containing two or four different MNW types, and fit them to linear combinations of the individual type signatures to determine the volume ratios of the types. We find that the signature which determines the ratios most accurately involves only the slope of each FORC at its reversal field, which requires only 2–4 data points per FORC curve, reducing the measurement time by a factor of 10 to 50 compared to measuring the full FORC.

Investigation of Nanofluid Natural Convection Heat Transfer in Open Ended L-shaped Cavities utilizing LBM

In this paper, laminar natural convection of copper/water nanofluid in an open-ended L-shaped cavity is investigated by Lattice Boltzmann Model (LBM). The results are compared by previous studies, that are in good agreement. Influences of Rayleigh number (Ra=〖10〗^3,〖10〗^4,〖10〗^5,〖10〗^6), cavity aspect ratio (AR=0.2, 0.4, 0.6) and volume concentration of Cu nanoparticles (0≤φ≤0.1) on the momentum, thermal fields and heat transfer in the enclosure are studied. Also, the effect of changing the boundary conditions, on the heat transfer rate has been investigated. It is observed that maximum heat transfer enhancement by adding the nanoparticles for Ra=〖10〗^6 with AR=0.4 (32.76%) occurs. Results illustrate that increasing the cavity aspect ratio decreases heat transfer rate for Ra=〖10〗^3 and Ra=〖10〗^4. The least and most heat transfer rate for Ra=〖10〗^5 occurs in enclosures by aspect ratios of 0.2 and 0.4 respectively, while it was observed at Ra=〖10〗^6 for minimum and maximum rate of heat transfer the opposite behavior that at Ra=〖10〗^5 occurs.

Exploring the Impact of Morphology on the Properties of Biodegradable Nanoparticles and Their Diffusion in Complex Biological Medium.

Nanoparticle morphology (size, shape, and composition) and surface chemistry are the determining factors underpinning the efficacy of such materials in therapeutic applications. The size, shape, and surface chemistry of a nanoparticle can strongly influence key properties such as interactions with diverse biological fluids and interfaces and, in turn, impact the delivery of bioactive cargo, modulating therapeutic performance. This is exemplified in ocular drug delivery, where potential therapeutics must navigate complex biological media such as the gel-like vitreal fluid and the retina. Biodegradable block copolymer amphiphiles are a robust tool for the engineering of various types of self-assembled nanoparticles with diverse morphologies ranging from spherical and tubular polymersomes to spherical and worm-like micelles. Here, we explore the effect of morphological features such as shape and surface chemistry upon the interactions of a series of copolymer nanoparticles with retinal (ARPE-19) cells and the release of a low solubility drug (dexamethasone) that is currently used in ocular therapy and study their diffusion in vitreous using ex vivo eyes. We demonstrate that both aspect ratio and surface chemistry of nanoparticles will influence their performance in terms of cell uptake, drug release, and diffusion with high aspect ratio shapes demonstrating enhanced properties in relation to their spherical counterparts.

One-step synthesis of Cu3N, Cu2S and Cu9S5 and photocatalytic degradation of methyl orange and methylene blue

Herein we report on a novel one-step synthesis of copper-rich Cu3N, Cu2S and Cu9S5 nanoparticles by using the surfactant dodecanethiol as a sulfur source to substitute the nitrogen in Cu3N using the Pearson acid-base concept. The Cu3N nanoparticles are indexed to a cubic anti-ReO3 phase, whilst the Cu2S nanoparticles are indexed to the alpha low cubic phase and Cu9S5 to a rhombohedral phase. The Williamson-Hall method is then used to estimate the sizes from the x-ray diffraction patterns. The estimated sizes are larger than the sizes observed from transmission electron microscopy. X-ray photoelectron spectroscopy confirms the formation of Cu3N, Cu2S and Cu9S5 nanoparticles. The oxidation state of copper in Cu3N and Cu2S is +1 with Cu9S5 having both Cu1+ and Cu2+ present. In addition the S 2p high resolution spectrum for Cu9S5 shows the presence of S2− and (S2)2−. The TEM shows the formation of cubic Cu3N nanoparticles (41 nm) as well as hexagonal Cu2S (27 nm), and elongated Cu9S5 nanoparticles (aspect ratio 1.8). These nanoparticles have direct band-gap transitions of 2.41 eV, 2.75 eV and 2.36 eV respectively. The blue-shifting of photoluminescence spectrum of the Cu3N nanoparticles is indicative of the presence of surface traps while Cu2S and Cu9S5 show near band-edge emission indicative of defect-free samples. The nanoparticles are then used as photocatalysts to degrade methyl orange and methylene blue dyes. The Cu3N photocatalyst degrades 89 % of 20 ppm methyl orange dye in a 1st order reaction with the degradation products being aniline and C5H6N2SO3- fragments whilst the Cu9S5 is the best catalyst at degrading 20 ppm methylene blue (79 %). The methylene blue degradation follows a 2nd order reaction and aniline is the only detectable degradation product.

Free convection with MWCNT/water nanofluid having varying aspect ratio of MWCNT nanoparticle in thermally undulated enclosures

The Aspect ratio of carbon nanotubes (CNTs) in cavities of different geometrical aspect ratio is one of the critical parameters of the design in thermal engineering. The present work documented a numerical simulation of 2D, steady and laminar free convection in rectangular cavities with different aspect ratios filled with water-based nanofluid. The nanoparticle considers in the present work is MWCNT with varying average diameter and length consequently varying aspect ratio. The Navier–Stokes and energy equations are solved numerically, coupling Thang et al. [43] model for calculating the effective thermal conductivity and Brenner and Condiff [44] model for determining the effective dynamic viscosity. The results are presented in the form of streamlines, isotherms, vertical velocity and Nusselt numbers. The novelty of the present study is to find the effect of MWCNT nanoparticle aspect ratio on fluid flow and heat transfer. Maximum of about 65% increment in average Nusselt number is observed at maximum aspect ratio (length/diameter) of 6 × 104 for any temperature undulation and cavity aspect ratio. Maximum MWCNT aspect ratio (or minimum diameter) is proposed for better heat transfer. A range of Rayleigh number is observed for better heat transfer for different temperature undulation value at the left wall.

Melting heat transfer of power-law non-Newtonian phase change nano-enhanced n-octadecane-mesoporous silica (MPSiO2)

The heat transfer removal from heated elements in different engineering devices is the main challenge for each engineer in various fields. This problem can be solved using an effective heat-transfer agent or by increasing the heat transfer surface. The present work is devoted to an opportunity to use the phase change material with nanoparticles for an intensification of heat removal within a gap between two coaxial vertical isothermal cylinders. The analysis was performed numerically using the Galerkin finite element approach in the case of the non-Newtonian nature of the nano-enhanced PCM. The power-law was used for the description of the non-Newtonian behavior of the considered material. For the solution to the Stefan problem, a deformed mesh method, based on the Arbitrary Lagrangian–Eulerian (ALE), was used. The developed computational code was validated using the numerical and experimental data of other authors. The effects of the nanoparticles volume fraction, aspect ratio and Fourier number on the melting process were investigated. It has been revealed that the inclusion of nanoparticles within the phase change material leads to both less intensive melting of the material and a reduction of the average Nusselt number.

Influence of particle aspect ratio and ability to aggregate on electrical conductivity of fiber-forming polymer composites

Fiber-forming polymer composites filled with carbon nanoparticles of three types (carbon black is a spherical filler; carbon nanofibers and carbon nanotubes are anisotropic nanoparticles) were produced by melt technology. Electrical conductivity of the fiber-forming polymer composites was measured; a function of the filler concentration and the percolation thresholds were determined. It was found that an increase in the aspect ratio of carbon nanoparticles leads to a decrease in the percolation threshold. The correlation between the axial ratio, stiffness, filler concentration and electrical conductivity of the percolation cluster in fiber-forming polymer composites was analysed.

A Simulation Work for the Influences of Aggregation/Agglomeration of Clay Layers on the Tensile Properties of Nanocomposites

This study examines the aggregation/agglomeration of layered clay in polymer nanocomposites and discusses their influences on nanoparticle characteristics and mechanical properties using appropriate equations. The effective volume fraction, specific surface area, and aspect ratio of layers are calculated in samples containing both single and aggregated/agglomerated nanoparticles. The Young’s modulus and yield strength of nanocomposites are predicted based on the effective characteristics of layers. The aggregation/agglomeration decreases the effective levels of volume fraction, aspect ratio, and specific surface area of nanoparticles. As a result, researchers should prevent the accumulation of clay layers in nanocomposites and encourage the exfoliation of single layers causing optimal properties.

Simulating natural convection and entropy generation of a nanofluid in an inclined enclosure under an angled magnetic field with a circular fin and radiation effect

Natural convection and radiation heat transfer of alumina (Al2O3)–water nanofluid are assessed in an enclosure under a magnetic field in different angles. The enclosure is a cavity at an angle of 45° with respect to the horizon, and a circular quadrant fin with the temperature Th is placed at the bottom corner of the cavity. The right wall is considered at the temperature Tc, and the rest of the walls are defined as adiabatic. The governing equations of flow are solved using algebraic finite volume method and the SIMPLE algorithm. In this work, the entropy generation is also evaluated other than heat transfer. The parameters in the present work include Rayleigh and Hartmann numbers, radiation parameter, magnetic field angle, nanoparticles volume fraction and aspect ratio. The results indicate higher Nusselt number and entropy generation and a lower Bejan number for a higher Rayleigh number and a lower Hartmann number. Addition of 6% of the nanoparticles causes an increase of 10% in the heat transfer rate and 11% in the entropy generation in the absence of radiation. The addition of the radiation mechanism to the enclosure leads to an increase in the heat transfer rate and entropy generation. It is also demonstrated that the vertical magnetic field is more intense than the horizontal magnetic field in the enclosure. With an increase in the fin aspect ratio from 0.3 to 0.7, the rate of heat transfer and entropy generation increases by 36 and 27%, respectively.

Size and aspect ratio dependency of sensitivity of ellipsoidal metal nanoparticle based liquid sensor

Detection of bio chemical species in a liquid is very important for research and technical purposes. In the last decade, metallic nanoparticles have been shown to be potential for such measurement. Resonance wavelength (or frequency) of free electron oscillation on metallic nanoparticle surface is very sensitive to tiny changes of its surrounding environment. Change in surrounding medium shifts the resonance wavelength with a slope determined mainly by the size and geometry of nanoparticle. We numerically optimized size and aspect ratio of silver and gold nanoparticles to obtain the highest sensing sensitivity. Here, sensitivity is defined as the slope of resonance wavelength on refractive index of liquid. We found that size, aspect ratio, and material of metal affect sensing sensitivity of metal nanoparticle based sensor significantly.

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.