Effect Of Nanoparticle Shape Research Articles

Gold nanoparticle-assisted polymerase chain reaction: effects of surface ligands, nanoparticle shape and material

The concentration, shape, material, and surface functionalization effects of gold nanoparticles on PCR outcome have been studied with two PCR gene diagnostic models.

Effect of gold nanoparticle shapes for phototherapy and drug delivery

In this study, we compared three different hybrid gold nanoparticle shapes (spherical, rod and star) for photothermal therapy and the delivery of doxorubicin.

Doping liquid crystals with nanoparticles. A computer simulation of the effects of nanoparticle shape

We have studied, using Monte Carlo computer simulations, the effects that nanoparticles of similar size and three different shapes (spherical, elongated and discotic) dispersed at different concentrations in a liquid crystal (LC), have on the transition temperature, order parameter and mobility of the suspension. We have modelled the nanoparticles as berry-like clusters of spherical Lennard-Jones sites and the NP with a Gay-Berne model. We find that the overall phase behaviour is not affected by the addition of small amounts (xN = 0.1-0.5%) of nanoparticles, with the lowest perturbation obtained with disc-like nanoparticles at the lowest concentration. We observe a general decrease of the clearing temperature and a reduction in the orientational order with a change in its temperature variation, particularly in the case of the xN = 0.5% dispersions and with a more pronounced effect when the nanoparticles are spherical.

Mixed convection due to rotating cylinder in an internally heated and flexible walled cavity filled with SiO2–water nanofluids: Effect of nanoparticle shape

In this study, numerical investigation of mixed convection in a square cavity filled with SiO2 nanofluid and volumetric heat generation is performed under the effect of an inner rotating cylinder and a flexible side wall. The top wall of the cavity is kept at constant cold temperature while the bottom wall is at hot temperature and the other walls of the cavity and the cylinder surface are assumed to be adiabatic. The finite element method is utilized to solve the governing equations. The Arbitrary Lagrangian–Eulerian method is used to describe the fluid motion with the flexible wall of the cavity in the fluid–structure interaction model. The effects of external Rayleigh number (between 103 and 5×105), internal Rayleigh number (between 104 and 106), Young's modulus of the flexible wall (between 5×102 and 106), angular rotational speed of the cylinder (between −2000 and 2000) and nanoparticle volume fraction (between 0 and 0.03) on the fluid flow and heat transfer are numerically studied for different solid nanoparticle shapes (spherical, cylindrical, brick and blade). It is observed that as the value of external Rayleigh number increases, internal Rayleigh number and elastic modulus of the flexible wall decrease, the local and averaged heat transfer enhances. The averaged heat transfer enhances with cylinder rotation in both directions for all nanoparticle types. Among all nanoparticle shapes, cylindrical ones show the best performance and spherical ones show the worst performance for heat transfer enhancement.

Effects of Nanoparticle Shape and Size on Optical Properties of LaB6

The optical response of lanthanum hexaboride (LaB6) nanoparticles has been investigated by both theoretically and experimentally. The LaB6 nanoparticles obtained by solid-state reaction could avoid serious surface oxidization and exhibit excellent optical performance. The discrete dipole approximation (DDA) has been used to investigate the optical response of LaB6 nanoparticles with different sizes and different shapes. The calculation results coincide with the experimental results and reveal that the largest extinction peak value appears at 60 nm for cubic particles and 40 nm for spherical particles, respectively. Our calculation results show that the existence of the largest extinction peak value is not only due to the surface oxides but also relate to the particle shape of LaB6 compound. In addition, the LaB6 nanoparticles with cubic and spherical shapes exhibit different optical responses, and the cubic particles exhibit stronger near infrared (NIR) extinction than spherical particles. With increasing particle size, the extinction peak value of spherical particle decreases more rapidly than that of cubic ones.

Evaluation of Nanoparticle Shape Effect on a Nanofluid Based Flat-Plate Solar Collector Efficiency

Solar thermal energy is a very convenient source of heating which is environmentally benign. Solar collectors convert solar radiation into heat and transfer the heat to a medium. Flat-plate solar collectors are the most common and cost effective devices for exploiting solar energy. However, these systems have relatively low efficiency due to the poor thermo-physical properties of working fluid. Dispersing of nanometer sized particles into the base fluid is proposed as an efficient method to improve heat transfer properties of the working fluid. In order to evaluate the thermal performance of nanofluid in a solar collector, firstly, it is essential to understand the thermo-physical variations of base fluid through addition of nanoparticles. Thermo-physical properties of base fluid vary with parameters such as particle concentration, particle diameter, and particle shape. In this study the effect of these parameters are explored on thermal performance of a flat-plate solar collector theoretically. Investigating shape effect of particles on collector efficiency is a highlight in this study. It is observed that increasing nanoparticles volumetric concentration leads to enhancenement in flat-plate collector efficiency. Reversely, particle size enhancement reduces the efficiency. In addition, particle shape affects collector efficiency. For different shapes of particles, including spherical, brick, cylinders, platelets, and blades, the blade shape particles relatively have the highest efficiency.

Metallic nanoparticle shape and size effects on aluminum oxide-induced enhancement of exciton-plasmon coupling and quantum dot emission.

We investigate the shape and size effects of gold metallic nanoparticles on the enhancement of exciton-plasmon coupling and emission of semiconductor quantum dots induced via the simultaneous impact of metal-oxide and plasmonic effects. This enhancement occurs when metallic nanoparticle arrays are separated from the quantum dots by a layered thin film consisting of a high index dielectric material (silicon) and aluminum oxide. Our results show that adding the aluminum oxide layer can increase the degree of polarization of quantum dot emission induced by metallic nanorods by nearly two times, when these nanorods have large aspect ratios. We show when the aspect ratio of these nanorods is reduced to half, the aluminum oxide loses its impact, leading to no improvement in the degree of polarization. These results suggest that a silicon/aluminum oxide layer can significantly enhance exciton-plasmon coupling when quantum dots are in the vicinity of metallic nanoantennas with high aspect ratios.

The effect of nanoparticle shape on the thermal resistance of a flat-plate heat pipe using acetone-based Al2O3 nanofluids

In this paper, we experimentally investigate the effect of the shape of nanoparticles in acetone-based Al2O3 nanofluids on the thermal resistance of a flat-plate heat pipe. Acetone-based Al2O3 nanofluids containing sphere-, brick- and cylinder-shaped nanoparticles were prepared, using the two-step method without any surfactants or additives. The flat-plate heat pipes are manufactured with the prepared three nanofluids. The thermal resistances of the flat-plate heat pipes are experimentally obtained. The results show that the thermal resistances of the flat-plate heat pipes with nanofluids containing sphere-, brick- and cylinder-shaped nanoparticles are reduced to 33%, 29%, and 16%, respectively, compared with the thermal resistance of the flat-plate heat pipe with pure acetone. Based on the results, we demonstrate that the shape of nanoparticles in working nanofluids significantly affects the thermal resistance of the heat pipes. Finally, we discuss why nanoparticle shape in nanofluids reduces the thermal resistance of the flat-plate heat pipe using a theoretical approach presented in literature.

The shape effects of nanoparticles suspended in HFE-7100 over wedge with entropy generation and mixed convection

The flow of mixed convection nanofluid over wedge under the effects of porous medium is investigated. The HFE-7100 Engineered Fluid having Nimonic 80a metal nanoparticles of spherical and non-spherical shapes with different sizes is used. The particle shape effects on Bejan number and entropy generation are taken into account. The system of partial differential equations is first written in terms of ordinary differential equations using adequate similarity transformations and then solved analytically. Analytical solutions of the resulting equations are obtained for the velocity and temperature profiles. Simultaneous effects of porous medium, particle volume friction, mixed convection parameter, and angle of wedge in the presence of different shapes nanoparticles are demonstrated graphically. Effects of particle concentrations, sizes on wall stress, heat transfer coefficient of Skin friction, and Nusselt are discussed in the form of tables.

Effect of particle shape on suspension stability and thermal conductivities of water-based bohemite alumina nanofluids

The suspension stability and thermal conductivity of water-based bohemite alumina nanofluids created using nanoparticles of various shapes (brick, platelet, and blade) at concentrations from 0.3 vol% to 7.0 vol% were theoretically and experimentally investigated. To quantitatively examine the effect of nanoparticle shape on suspension stability, this study uses the laser-scattering method rather than the zeta-potential measurement or the sedimentation test because both the zeta-potential and sedimentation tests cannot systematically represent the suspension stability of nanofluids. Using the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory, we explain why the suspension stability varies with nanoparticle shape despite similar volume fraction of nanoparticles, pH, and temperature. The thermal conductivities are also measured by the transient hot wire method, which was developed in house. Experimental data are compared with theoretical results predicted by the Hamilton–Crosser model, which considers the effect of nanoparticle shape. It is shown that the model cannot predict nanofluids thermal conductivity relative to nanoparticle shape. Finally it is clearly shown that the thermal conductivity of nanofluids strongly depends on the suspension stability of bohemite alumina with various shapes.

Influence of copper oxide nanoparticle form and shape on toxicity and bioaccumulation in the deposit feeder, Capitella teleta

Few in vivo studies have been conducted to assess how nanoparticle (NP) characteristics such as particle form and shape affect their toxicity and bioaccumulation. In the present study, the deposit feeder, Capitella teleta, was used to investigate the influence of copper form (CuO NPs, micron-sized CuO particles, and aqueous Cu) and CuO NP shape (spheres, rods and platelets) on toxicity and bioaccumulation through sediment exposures of approximately 250 μg Cu/g dw sed. There were no effects of nanoparticle form or shape on mortality or growth rate during the exposure period. However, mortality increased to approximately 26.3% on average in all Cu treatments after the depuration period indicating a delayed effect of Cu exposure, despite more than 90% depuration of Cu during this period. A significant effect of nanoparticle shape was detected on body burden, the gross uptake rate constant and the depuration rate constant, suggesting preferential accumulation of rods by the worms. We recommend that additional sublethal endpoints and longer exposure durations should be examined to fully understand the environmental risks of CuO nanoparticles compared to other forms of Cu entering marine sediment systems.

Evaluation of crystallinity and gas barrier properties of films obtained from PLA nanocomposites synthesized via “in situ” polymerization of l-lactide with silane-modified nanosilica and montmorillonite

The effects of nanoparticles shape and surface modification on crystallinity and on gas and vapor properties of nanocomposites polylactide (PLA) films were evaluated. Films were prepared via solvent casting from PLA nanocomposites obtained by in situ polymerization of l-lactide using two different nanoparticles: nanosilica (NS) and an organically-modified montmorillonite (MMT), Cloisite® 15A. To improve the compatibility between the polymer and the nanoparticles, NS and MMT were also modified with different amounts of two silanes, 3-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane. Thermal analyses indicate that nanoparticles (both with and without silanes on the surface) enhance crystallization processes and the effect of NS is much higher than the effect of MMT. The presence of NS nanoparticles, especially when modified with silanes, contribute in greatly enhancing crystallinity and in lowering permeability to O2 and CO2; values of O2 and CO2 permeability were reduced up to 80% and 50% respectively, compared to pure PLA; water vapor (WV) permeability is significantly affected by the presence of the nanoparticles but not by their shape and by modification with silanes. The in situ-synthesis permits to use lower amounts of nanoparticle in comparison to melt extrusion or blending processing techniques, in order to achieve the same or better performances, thanks to an improved dispersion of the fillers, that is obtained also due to the surface modification.

First-principles calculations of the dissolution and coalescence properties of Pt nanoparticle ORR catalysts: The effect of nanoparticle shape

The degradation of Pt nanoparticles (NPs) in fuel cell cathodes leads to the loss of the precious metal catalyst. While the effect of NP size on Pt dissolution has been studied extensively, the influence of NP shape is largely unexplored. Because of the recent development of experimental methods to control the shape of metal NPs, rational guidelines/insights on the shape effects on NP stability are imperative. In this study, first-principles calculations based on density functional theory were conducted to determine the stability of 1–2 nm Pt NPs against Pt dissolution and coalescence with respect to NP shape. Toward dissolution, the stability of the Pt NPs increases in the following order: Hexagonal close-packed < icosahedral < cuboctahedral < truncated octahedral. This trend is attributed to the synergy of the oxygen adsorption strength and the local coordination of the Pt atoms. With respect to coalescence, the size of a NP is related to its propensity to coalesce or detach/migrate to form larger particles. The stability of the Pt NPs was found to increase in the following order: Hexagonal close-packed < truncated octahedral < cuboctahedral < icosahedral, and was correlated with the cohesive energies of the particles. By combining the characteristic stabilities of the shapes, new “metal-interfaced” Pt-based coreshell architectures were proposed that should be more stable than pure Pt nanoparticles with respect to both dissolution and coalescence.

The effects of Au nanoparticle size (5–60 nm) and shape (sphere, rod, cube) over electronic states and photocatalytic activities of TiO2studied by far- and deep-ultraviolet spectroscopy

While there was little shape dependence, smaller Au nanoparticles induced larger electronic state changes and higher photocatalytic activities.

Shape effects of Pt nanoparticles on hydrogen production via Pt/CdS photocatalysts under visible light

The photocatalytic activity of Pt/CdS photocatalysts strongly depends on both the shape and size of the Pt particles.

Aggregate size and structure determination of nanomaterials in physiological media: importance of dynamic evolution

Most in vitro nanotoxicological assays are performed after 24 h exposure. However, in determining size and shape effect of nanoparticles in toxicity assays, initial characterization data are generally used to describe experimental outcome. The dynamic size and structure of aggregates are typically ignored in these studies. This brief communication reports dynamic evolution of aggregation characteristics of gold nanoparticles. The study finds that gradual increase in aggregate size of gold nanospheres (AuNS) occurs up to 6 h duration; beyond this time period, the aggregation process deviates from gradual to a more abrupt behavior as large networks are formed. Results of the study also show that aggregated clusters possess unique structural conformation depending on nominal diameter of the nanoparticles. The differences in fractal dimensions of the AuNS samples likely occurred due to geometric differences, causing larger packing propensities for smaller sized particles. Both such observations can have profound influence on dosimetry for in vitro nanotoxicity analyses.

Atomistic investigation of the nanoparticle size and shape effects on ionic conductivity of solid polymer electrolytes

Adding nanoparticle fillers is a potential route to enhance room temperature ionic conductivity of solid polymer electrolytes. In this work, we use molecular dynamics simulation to elucidate the role of nano-scale filler size and shape on ionic conductivity. Our key conclusions are that the addition of nanofillers can affect the salt dissociation, lithium-ion mobility, and the dynamics of polymer chains. The repulsive nanofillers of different sizes appear to suppress ion-cluster formation and enhance lithium ion mobility. Smaller size nanofillers are found to be comparatively more effective in increasing the mobility of lithium ions while shape effects appear to be insignificant.

Shape dependence of the band gaps in luminescent silicon quantum dots

Silicon nanoparticles exhibit quantum confinement and function as optoelectronic devices whose optical properties are known to depend strongly on size and surface termination. The effect of nanoparticle shape on optical properties, however, has not yet been investigated. In this work we use tight binding and density functional theory simulations to study the HOMO–LUMO gaps of hydrogen-terminated silicon nanoparticles as a function of shape and size. It is shown that optical properties are strongly dependent upon nanoparticle shape, and in particular that octahedral nanoparticles exhibit significantly (up to 0.2 eV) larger band gaps than cubic or pseudo-spherical nanoparticles of the same volume. Control of the shape of nanoparticles via the tuning of the thermodynamic conditions in which they are formed may allow the formation of silicon nanoparticles with emission wavelengths running across the full visible range.

Size-tunable synthesis of monodisperse thorium dioxide nanoparticles and their performance on the adsorption of dye molecules

We report a facile method to synthesize monodisperse, uniform and size-controllable thorium dioxide nanoparticles via a hydrothermal precursor synthesis and a subsequent calcination treatment. Highly uniform spherical precursor nanoparticles with a tunable diameter of 38–274 nm and monodisperse irregular precursor nanoparticles with a size range of 20–45 nm can be successfully synthesized using thorium nitrate pentahydrate, urea and glycerol as the metal source, nucleation agent, and size-controlling agent, respectively. The chemical composition, growth process, and size control of the precursor nanoparticles have been systematically investigated, and a probable formation mechanism of these nanoparticles was also proposed. Calcination of precursor nanoparticles at 800 °C leads to the formation of uniform thorium dioxide nanoparticles without any morphological deformation. Furthermore, the size and shape effects of thorium dioxide nanoparticles on the uptake of dye molecules have been studied. The corresponding adsorption behaviors of as-prepared samples can be elucidated very well by the nitrogen adsorption–desorption analysis.

First and second laws analysis of a minichannel-based solar collector using boehmite alumina nanofluids: Effects of nanoparticle shape and tube materials

This paper evaluates the first and second laws for a flat plate minichannel-based solar collector where the working fluid is a suspension of boehmite alumina nanoparticles in a mixture of water and ethylene glycol. Four different shapes of nanoparticles, including platelets, blades, cylinders, and bricks are selected for this study. The results of Nusselt number, heat transfer coefficient, outlet temperature, and entropy generation are presented for different shapes of nanoparticles and volume concentrations up to 4% in turbulent flow. Two different solar collectors are investigated so that in one of them the tubes and absorber plate are made of copper and in another the material is of steel. It is found that the platelet shaped nanoparticles show the lowest heat transfer coefficient while bricks, except at the highest volume fraction, i.e. 4%, display the highest heat transfer coefficient. The heat transfer coefficient for copper tubes is lower than that of steel tubes. The findings indicate that, independent of nanoparticle shape, the outlet temperature increases by adding the nanoparticles but the rate of increase for platelets is lowest. The results of entropy generation analysis for copper tubes elucidate that the entropy generation rate is minimized by using brick shaped particles with volume fraction of 2%, while for steel tubes the minimum entropy generation is achieved by using blade shaped particles with volume fraction of 4%. In mass flow rate of 0.5kg/s, the entropy generation rate for steel tubes is, on average, about 11% higher than copper tubes and this value attains 18% when the mass flow rate increases from 0.5 to 0.75kg/s.