Nanoparticle Polydispersity Can Strongly Affect In Vitro Dose

When nanomaterials meet the biological world, the cellular interaction of nanoparticles is routinely assessed in in vitro systems. Establishing dose–response relationships requires that the dose of nanoparticles delivered to the cell is accurate and precise. Nanoparticles as such or coated with high molecular‐weight compounds are rarely uniform and the influence of heterogeneity, including polydispersity both in size and mass density, on the delivered dose is never studied before. Furthermore, a probabilistic term describing particle adherence to cells is introduced and the importance is discussed. By tracing the movement of discrete particles via modeling, it is found that the influence of heterogeneity cannot be neglected when the average particle size promotes settling over diffusion. However, the influence of polydispersity on the delivered cellular dose is less critical for particulate systems whose mean size promotes diffusion. The influence of a non‐instantaneous particle association to the cell is negligible for particles whose motion is dominated by settling, but it is relevant for small particles whose motion is governed by diffusion.     

Effects of Continuous Size Distributions on Pressures of Granular Gases

Direct Monte Carlo simulations are employed to investigate the granular pressures in granular materials with a power-law particle size distribution. Specifically, smooth circular discs of uniform material density are engaged in a two-dimensional rectangular box, colliding inelastically with each other and driven by a homogeneous heat bath at zero gravity. The resulting pressures are found to decrease as the widths of particle size distribution are increased. Moreover, the granular pressures in power-law systems are found to be unequally distributed among the various sizes of particles, with large particles possessing more pressure than their smaller counterparts. The width-dependent nature of the total pressures is induced by the more dispersion of smaller particles in the system as the particle size distribution is widened.     

Dynamic Light Scattering Measurement of Nanometer Particles in Liquids

Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.     

Characterisation of silica nanoparticles prior to in vitro studies: from primary particles to agglomerates

The size, surface charge and agglomeration state of nanoparticles under physiological conditions are fundamental parameters to be determined prior to their application in toxicological studies. Although silica-based materials are among the most promising candidates for biomedical applications, more systematic studies concerning the characterisation before performing toxicological studies are necessary. This interest is based on the necessity to elucidate the mechanisms affecting its toxicity. We present here TEM, SAXS and SMPS as a combination of methods allowing an accurate determination of single nanoparticle sizes. For the commercial material, Ludox TM50 single particle sizes around 30 nm were found in solution. DLS measurements of single particles are rather affected by polydispersity and particles concentration but this technique is useful to monitor their agglomeration state. Here, the influence of nanoparticle concentration, ionic strength (IS), pH and bath sonication on the agglomeration behaviour of silica particles in solution has been systematically investigated. Moreover, the colloidal stability of silica particles in the presence of BSA has been investigated showing a correlation between silica and protein concentrations and the formation of agglomerates. Finally, the colloidal stability of silica particles in standard cell culture medium has been tested, concluding the necessity of surface modification in order to preserve silica as primary particles in the presence of serum. The results presented here have major implications on toxicity investigations because silica agglomeration will change the probability and uptake mechanisms and thereby may affect toxicity.     

Dynamic light scattering of a concentrated multicomponent spherical particle solution

The“measured”dunamic structure function of highly concentrated and smallspherical colloidal system with a narrow distribution of particle sizes can be expressed in termsof the sum of two independent modes due to collective diffusion and polydispersity fluctuationsrespectively.The“measured”static structure functions S~M(K) is derived,and applied to cal-culate the polydispersity distribution.The relationship between the moments of the gammaparticle size distribution and the moments determined by a dynamic light scattering measure-ment is developed for the case when the particles are small and spherical.     

Dispersion of crystalline powder materials in gaseous media of different chemical compositions

The process of grinding of rutile and barite crystalline powders in a laboratory ball mill in different types of gaseous media (air, nitrogen, helium) has been investigated. Comparative evaluations of the intensity of the dispersion of these minerals have been performed and the particle sizes of powders obtained in different modes of their dispersion have been measured. A sharp increase in the intensity of this process in the helium medium as compared to the air and nitrogen media has been revealed and ultrafine-grained particles of barite powders have been obtained. The results of the performed investigations have demonstrated that the helium medium can be recommended for producing nanoparticles of powder materials in modern types of ball and bead mills with a drastic decrease in the time and energy consumptions required for their preparation.     

Efficient adsorption and photocatalytic degradation of Congo red onto hydrothermally synthesized NiS nanoparticles

The influence of the length of the cation alkyl chain on the dispersibility by ultrasonic treatment of TiO₂ nanopowders in hydrophilic imidazolium-based room temperature ionic liquids was studied for the first time by dynamic light scattering and advanced rheology. TiO₂ nanopowders had been synthesized by chemical vapor synthesis (CVS) under varied conditions leading to two different materials. A commercial nanopowder had been used for comparison. Characterizations had been done using transmission electron microscopy, X-ray diffraction, nitrogen adsorption with BET analysis, and FT-IR spectroscopy. Primary particle sizes were about 6 and 8 nm for the CVS-based and 26 nm for the commercial materials. The particle size distribution in the dispersion was strongly influenced by the length of the cation alkyl chain for all the investigated powders with different structural characteristics and concentrations in the dispersion. It was found that an increase of the alkyl chain length was beneficial, leading to a narrowing of the particle size distribution and a decrease of the agglomerate size in dispersion. The smallest average nanoparticle sizes in dispersion were around 30 nm. Additionally, the surface functionality of the nanoparticles, the concentration of the solid material in the liquid, and the period of ultrasonic treatment control the dispersion quality, especially in the case of the ionic liquids with the shorter alkyl chain. The influence of the nanopowders characteristics on their dispersibility decreases considerably with increasing cation alkyl chain length. The results indicate that ionic liquids with adapted structure are candidates as absorber media for nanoparticles synthesized in gas phase processes to obtain liquid dispersions directly without redispergation.     

Characterizing char particle fragmentation during pulverized coal combustion

A particle population balance model was developed to predict the oxidation characteristics of an ensemble of char particles exposed to an environment in which their overall burning rates are controlled by the combined effects of oxygen diffusion through particle pores and chemical reactions (the zone II burning regime). The model allows for changes in particle size due to burning at the external surface, changes in particle apparent density due to internal burning at pore walls, and changes in the sizes and apparent densities of particles due to percolation type fragmentation. In percolation type fragmentation, fragments of all sizes less than that of the fragmenting particle are produced. The model follows the conversion of particles burning in a gaseous environment of specified temperature and oxygen content. The extent of conversion and particle size, apparent density, and temperature distributions are predicted in time.Experiments were performed in an entrained flow reactor to obtain the size and apparent density data needed to adjust model parameters. Pulverized Wyodak coal particles were injected into the reactor and char samples were extracted at selected residence times. The particle size distributions and apparent densities were measured for each sample extracted. The intrinsic chemical reactivity of the char to oxygen was also measured in experiments performed in a thermogravimetric analyzer. Data were used to adjust rate coefficients in a six-step reaction mechanism used to describe the oxidation process.Calculations made allowing for fragmentation with variations in the apparent densities of fragments yield the type of size, apparent density, and temperature distributions observed experimentally. These distributions broaden with increased char conversion in a manner that can only be predicted when fragmentation is accounted for with variations in fragment apparent density as well as size. The model also yields the type of ash size distributions observed experimentally.     

Nonlocal effects in the optical response of composite materials with metallic nanoparticles

A phenomenological model for the optical response of composite materials with metallic nanoparticles is presented. This model applies the conventional effective medium theories (EMT) but takes into account the spatial dispersion effects in the dielectric response of the metallic nanoparticles. This leads to an EMT that depends on the size of the particles. Numerical results from a model computation shows that this effect due to the nonlocal optical response of the nanoparticles can increase the resonant absorption frequency of the composite significantly for particles of very small sizes; and can lead to resonant absorption even in the Bruggeman symmetric EMT—a feature which is believed to be absent in the conventional treatment where local response for the metal particles has been assumed.     

Optical properties of hybrid plasmonic nanofluid based on core/shell nanoparticles

The plasmonic effect is used in nanofluid to help capture and absorb sunlight. The optical absorption is significantly enhanced as plasmonic effect excited. To obtain an enhanced absorption in a broad band, the hybrid plasmonic nanofluid is developed. It is composed of core/shell nanoparticles of different sizes. The overall absorption of hybrid nanofluid is examined. Compared to the nanofluid of single particle size, the hybrid nanofluid exhibits a broadband absorption. As particle size increases, the plasmon resonance peak is shifted to longer wavelength. The variation in the sizes of core/shell nanoparticles can broaden the absorption spectrum. In the near-infrared region, the proportion of different size particles has an obvious influence. With the increase of proportion of larger particles, the absorption band is broadened. Since the suspended nanoparticles have different sizes, the particle distribution in base fluid also has an effect on absorption of light. The large particle in upper has a broadband absorption, however, less energy can be transmitted to lower after the absorption of upper particles. The contribution from the particles in lower is relatively weak.     

Solvent effect in sonochemical synthesis of metal-alloy nanoparticles for use as electrocatalysts

Nanomaterials are now widely used in the fabrication of electrodes and electrocatalysts. Herein, we report a sonochemical study of the synthesis of molybdenum and palladium alloy nanomaterials supported on functionalized carbon material in various solvents: hexadecane, ethanol, ethylene glycol, polyethylene glycol (PEG 400) and Ionic liquids (ILs). The objective was to identify simple and more environmentally friendly design and fabrication methods for nanomaterial synthesis that are suitable as electrocatalysts in electrochemical applications. The particles size and distribution of nanomaterials were compared on two different carbons as supports: activated carbon and multiwall carbon nanotubes (MWCNTs). The results show that carbon materials functionalized with ILs in ethanol/deionized water mixture solvent produced smaller particles sizes (3.00 ± 0.05 nm) with uniform distribution while in PEG 400, functionalized materials produced 4.00 ± 1 nm sized particles with uneven distribution (range). In hexadecane solvents with Polyvinylpyrrolidone (PVP) as capping ligands, large particle sizes (14.00 ± 1 nm) were produced with wide particle size distribution. The metal alloy nanoparticles produced in ILs without any external reducing agent have potential to exhibit a higher catalytic activity due to smaller particle size and uniform distribution.     

Size-dependant heating rates of iron oxide nanoparticles for magnetic fluid hyperthermia

Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ∼15 nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions.     

Continuous Size Classification of Nanoparticles Utilizing Brownian Motion in Microchannel Size Exclusion Chromatography

This study presents a new method for classifying the sizes of colloidal nanoparticles of below 100 nm in diameter in liquid dispersion using a microchannel size exclusion chromatography (SEC) chip. This chip can classify polydisperse colloidal nanoparticles containing a mix of two monodisperse nanoparticles into several monodisperse particle populations. The particles classified by the SEC chip are then sequentially analyzed by a photon correlation spectroscopy (PCS) method in combination with a flow cell. Two different pillar patterns of such SEC chips were used in experiments to investigate the effects of these patterns on the nanoparticle classification performance. The results obtained were compared with those from a numerical simulation. Standard polystyrene latex particles with diameters of 20 nm and 100 nm were used in this study. The usefulness of this methodology was verified since the simulation and measurement results were in good agreement with each other.     

Particle surface treatment for nanocomposites containing ceramic particles

Polymer matrix composites containing dispersed ceramic nanoparticles were formed by UV activated photopolymerization from the reactive liquid monomer hexanediol-diacrylate (HDODA). The polymer forming reaction proceeds by a free-radical mechanism. In forming polymer composites that contain nanoparticles, dispersing the particles as discrete entities is critical for developing optimum properties. In the as-received condition, ceramic particles are aggregated. They must be dispersed in the monomer but if the particles are not surface treated and stabilized, they rapidly settle out of the suspension. Surface modification of the ceramic allows the particles to be suspended in the organic monomer and stabilizes the dispersion so that the particles will not reagglomerate. In this study silanes were employed as surface modifiers to disperse two nano-particulate ceramics in the HDODA monomer. The ceramic particles used are silicon carbide (SiC) and barium titanate (BaTiO₃). The shapes and sizes of the ceramic particles were established using transmission electron microscopy (TEM). A method for dispersing nanoparticles was developed in which silane-treated particles were stabilized so that they did not settle out of the liquid monomer. An analytical method based on atomic force microscopy (AFM) was used to characterize the particle distribution in the cured composites. Focusing on work with SiC nanoparticles in HDODA as a model system, the process for silane application was advanced so that it successfully yielded composites having no aggregates with particle sizes closely matching those of the neat ceramic particles.     

The dispersion of polymeric materials with the use of supercritical fluids

The dispersion of polyisobutylene was studied on a Thar RESS-100-2 test bench over the temperature and pressure ranges 45–120°C and 100–350 bar; 30–1000 nm particles were obtained. Particle size could be controlled by varying process parameters. A procedure for modifying polymer particles during rapid expansion of supercritical solutions was suggested. Modification suppressed agglomeration and caused particle coating with a modifier (NaCl). The use of supercritical fluid antisolvents was shown to be promising for the dispersion of polymers to nanosized particles. An experimental bench for performing such processes was described. A procedure for trapping nanoparticles prepared using antisolvents was suggested. Particles with sizes of 10 to 150 nm were obtained in the dispersion of polystyrene in the toluene-polystyrene-supercritical carbon dioxide system at 40–150 bar and temperatures of 40 and 100°C.     

Effect of particle size of graphites on electrical conductivity of graphite/polymer composite

The effect of particle size of graphite particles on the dispersion state of graphite particles and electrical conductivity of graphite/low-density polyethylene (LDPE) composites is investigated. Graphite particles which have plate-like and spherical shapes and mean particle sizes of 2.1 to 82.6 μm are used. Scanning electron microscopy observation showed that graphite particles are not aggregated and ordered along the direction of mixing-roll in the polymer matrix. X-ray diffraction measurements show that crystallite size of the (110) plane of polyethylene crystal and the crystallinity are significantly affected by the particle size of graphite particles. These results were interpreted as due to the orientation of PE crystallites. The electrical conductivity of composites changes discontinuously at the critical volume fraction of particles, Ø_c. The Ø_c values given by the percolation equation increase with decreasing of the particle size of graphites. The plate-like graphite particles with a mean particle size of 2.1 μm could induce conductivity at Ø_c of 0.135. The values of Ø_c increased linearly with increasing of the mean particle sizes of the plate-like graphites. The value of Ø_c of spherical graphite particle is the largest value, 0.292, in all specimens.     

Photoinduced formation of metal nanoparticles in γ-irradiated sodium-fluoride crystals

It is established that sodium nanoparticles with sizes of several hundreds of nanometers, several tens of nanometers, and several nanometers are formed in γ-irradiated photobleached NaF crystals. Along with randomly scattered particles, areas in which nanoparticles with sizes of tens of nanometers are grouped around a particle with a size of hundreds of nanometers are revealed. Mechanisms for color-center aggregation and nanoparticle formation are discussed.     

Morphology selection of nanoparticle dispersions by polymer media

Designable media can control properties of nanocomposite materials by spatially organizing nanoparticles. Here we theoretically study particle organization by ultrathin polymer films of grafted chains ("brushes"). Polymer-soluble nanoparticles smaller than a brush-determined threshold disperse in the film to a depth scaling inversely with particle volume. In the polymer-insoluble case, aggregation is directed: provided particles are nonwetting at the film surface, the brush stabilizes the dispersion and selects its final morphology of giant elongated aggregates with a brush-selected width.     

Estimation of the upper limit of aerosol nanoparticles penetration through inhomogeneous fibrous filters

The fully segregated flow model (FSFM) was formulated to describe filtration of aerosol nanoparticles in polydisperse fibrous filters made of fibers with different diameters. The model is capable of predicting significantly higher penetration of nanoparticles through polydisperse filters than it may be expected from the classical theory applied to a mean fiber diameter. The model was solved numerically in the case of the log-normal fiber size distribution, and a simple correlation between the actual penetration through a polydisperse filter and the one calculated for the geometric mean fiber diameter was proposed. Equivalent fiber diameter for deposition due to Brownian diffusion was determined and it was found to be dependent on particle size and filter’s polydispersity degree, being significantly greater than any mean fiber diameter. It was noted that it is impossible to select any one universal mean fiber diameter to describe penetration of nanoparticles with different sizes. It was also shown that in the case of a polydisperse fibrous filter the apparent exponent of the Peclet number based on the mean fiber diameter is greater than the expected value of −2/3 for diffusional deposition in a monodisperse filter. This prediction is in agreement with the available experimental data. The FSFM is expected to give the estimation of the upper limit of nanoparticles penetration in polydisperse fibrous filters.     

Effect of the temperature on the synthesis of (K,Na)NbO<Subscript>3</Subscript>-modified nanoparticles by a solid state reaction route

(Na_0.5K_0.5)NbO₃ (KNN)-modified nano-particulated powders, based on variations of sodium–potassium niobate, were synthesised by solid state reaction from carbonate starting materials. The nanoparticles were attained by an optimization of the raw materials particle size and particle refinement of the carbonates during their decomposition. Particle sizes between 50 and 200 nm have been obtained as a function of calcination (decomposition) temperature. The obtained powders showed a co-existence between a tetragonal phase and an orthorhombic phase. The optimization of the raw materials particle size and the particle refinement of the carbonates during their decomposition play a key role in the formation of the KNN-modified nano particles. The developed method is well suited for the production of KNN-modified nano powders at low cost for mass production.