Agglomeration Rate Research Articles

Bacterial uptake of silver nanoparticles in the presence of humic acid and AgNO3

Silver nanoparticles (AgNPs), potent antibiotic materials, have been found to cause cell-membrane damage and produce reactive oxygen species (ROS). The resultant structural change in the cell-membrane could cause an increase in cell permeability of silver ions and AgNPs. To address this issue further, in-vivo and in-vitro cytotoxicity testing of as-made nanomaterials was conducted to quantify and assess their nanotoxicity. Considering the behavior of AgNPs in the environment, toxicity may be reflected by differences in their physicochemical properties (size, agglomeration rate, adsorption properties on humic acid) dependency and toxicity depression. Therefore, we investigated the effect of the cellular uptake of AgNPs with the kinetics of agglomeration and adsorption. The amount of agglomerated and adsorbed AgNPs with sizes of <14 nm was higher than that for AgNPs with sizes of 90 and 140 nm. For 90 and 140 nm sized AgNPs, adsorption was more significant than agglomeration. It is noteworthy that the normal concept that smaller sized AgNPs are taken up more readily may be in error in cases of interactions of abiotic factors.

Agglomeration of microparticles in complex plasmas

Agglomeration of highly charged microparticles was observed and studied in complex plasma experiments carried out in a capacitively coupled rf discharge. The agglomeration was caused by strong waves triggered in a particle cloud by decreasing neutral gas pressure. Using a high-speed camera during this unstable regime, it was possible to resolve the motion of individual microparticles and to show that the relative velocities of some particles were sufficiently high to overcome the mutual Coulomb repulsion and hence to result in agglomeration. After stabilizing the cloud again through the increase of the pressure, we were able to observe the aggregates directly with a long-distance microscope. We show that the agglomeration rate deduced from our experiments is in good agreement with theoretical estimates. In addition, we briefly discuss the mechanisms that can provide binding of highly charged microparticles in a plasma.

Effects of CMP Slurry Additives on the Rate of Agglomeration of Alumina Particles

The rate of agglomeration of alumina particles in 1 mM KNO3 solutions with various additives with a range of pH values was measured. The suspensions tested contained only glycine and glycine, H2O2, benzotriazole, and sodium dodecyl sulfate. A fractal dimensional analysis was used to analyze the rate data to indicate the agglomeration mechanism. At pH 4 no aggregation was observed in the glycine only suspension, however significant aggregation occurred in the other suspension, reaching sizes greater than 3 μm within 2 min. Slow agglomeration was observed at pH 7.5 for both suspensions. Both suspensions at pH 10 showed immediate aggregation to mean sizes greater than 3 μm. However, adjustment of the suspension pH was sufficient to increase or reduce the aggregate size.

In Situ Detection of Altered Particle Size Distributions during Simulated Powdered Sorbent Injection for Mercury Emissions Control

During full-scale sorbent injection tests for mercury removal at coal-fired power plants (CFPPs), a common trend has been observed in which the overall mercury removal efficiency reaches a performance plateau as the sorbent injection rate increases. Two common explanations for this trend are (1) the increased sorbent injection rate induces increased rates of particle agglomeration within sorbent feeding lines, which eventually shifts the particle size distribution to larger sizes and reduces the available particle surface area for heterogeneous oxidation and adsorption, and (2) the increased sorbent injection rate limits the available acid gas concentration for heterogeneous oxidation of Hg0 to Hg2+. In this experimental study, an in situ measurement technique based on the principles of light extinction is used to assess the degree of particle agglomeration. The present in situ measurement technique applies a simple inline HeNe laser, and a sorbent feeder fluidizes powdered activated carbon (PAC) and drives the suspension through a length of rubber tubing to simulate the sorbent feeding process. Each experimental trial yields a time-dependent function of the light extinction ratio, I(t)/I0, for the time-dependent evolution of the PAC suspensions. Observed differences in I(t)/I0 for suspensions ejected directly from the feeder as compared to those directed through the tubing indicate changes in the overall particle size distribution. A numerical model of the experiment provides excellent agreement and facilitates interpretation of the experimental results.

Light-Induced Agglomeration and Diffusion of Different Particles with Optical Tweezers

The dynamic process of light-induced agglomeration of carbon nanotubes (CNTs), C60 and Escherichia coli (E.coli) in aqueous solutions is demonstrated using an optical tweezers system. Based on the results, the diameter of the agglomerated region and the agglomeration rate increase with the increasing laser power. After the saturation-stable period, CNTs diffuse completely, C60 clusters only diffuse partially, and E. coli never diffuses in the agglomeration region. Theoretical analyses show that the molecular polarization and thermal diffusion of particles play crucial roles in the diffusion process. The results indicate the possibility of using light to aggregate and sort nanoparticles.

Effects of CMP Slurry Additives on the Rate of Agglomeration of Alumina Particles

not Available.

Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 1: Experimental investigations

A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.

Gold nanoparticles: dispersibility in biological media and cell-biological effect

Spherical gold nanoparticles with a hydrodynamic diameter between 25 and 37 nm were prepared and stabilised with poly(N-vinylpyrrolidone) (PVP) or tris(sodium-m-sulfonatophenyl)phosphine (TPPTS). They were subjected to different cell culture media, e.g. pure RPMI, RPMI containing up to 10% of fetal calf serum (FCS), and RPMI containing up to 10% of bovine serum albumin (BSA), and the rate of agglomeration was studied by dynamic light scattering. In pure RPMI, a strong agglomeration was observed whereas in the RPMI–FCS and RPMI–BSA mixtures the particles remained well dispersed above 1 wt% protein concentration. The effect of PVP-stabilised gold nanoparticles on human mesenchymal stem cells (hMSC) was studied as well. No significant influence on the viability and chemotaxis was observed after incubation of hMSC with gold nanoparticles. However, gold nanoparticles induced the activation of hMSC as indicated by the release of IL-6 and IL-8.

Accumulation of nano-aluminium during combustion of composite solid propellant mixtures

Nano-aluminium particles are produced using the electric wire explosion process in an inert atmosphere at our institute. This paper reports the characterization of nanoaluminium particles in combination with other solid propellant ingredients for their thermal and combustion behaviour. High-heating-rate hot-stage microscopic experiments are performed with different mixtures of propellant ingredients. The effects of addition of nano-aluminium versus micron-sized aluminium in the middle lamina of sandwiches are analyzed for burning rates and by means of scanning electron microscope and transmission electron microscope micrographs of quench-collected aluminium agglomerates. Nano-aluminized sandwiches with thinner middle lamina show slightly higher burning rates than micron-sized aluminized ones. The quenched surface of nano-aluminized sandwiches shows relatively smaller aluminium agglomerates than with micron-sized aluminium. The resultant particle sizes of nano-aluminium agglomerates is in the range of 1–5 µm, which indicates a higher rate of agglomeration than with micro-aluminium, but these sizes are small relative to the agglomerates of the latter. This is also confirmed by quench-collected agglomerates of nano-aluminium emerging from the burning surface of a composite propellant.

Slurry Particle Agglomeration Model for Chemical Mechanical Planarization (CMP)

AbstractIn this work we propose a particle agglomeration model for chemical mechanical planarization (CMP) under the primary motivation of understanding the creation and behavior of the agglomerated slurry abrasive particles during the CMP process, which are a major cause of defectivity and poor consumable utility due to sedimentation.The proposed model considers the slurry composition as a colloidal suspension of charged colloidal silica in an electrically neutral aqueous electrolyte. First, a theoretical relationship between the measurable chemical parameters of the slurry's aqueous electrolyte, the surface potential of the abrasive particles, and corresponding zeta potential between the agglomerated abrasive particles is presented. Secondly, this zeta potential is used in a modified DVLO interaction potential model to determine the particle interaction potentials due to both the attractive van Der Waals forces and repulsive electrostatic interactions. Finally, the total interaction potential created is then used to define a stability ratio for slow versus fast agglomeration and corresponding agglomeration rate equations between particles; these are used in a discrete population balance framework to describe the final particle size distribution with respect to time and agglomerate composition.The proposed model will provide both a qualitative and quantitative description of agglomeration of abrasive slurry particles during CMP that can be extended to account for slurry composition or abrasive particle type, enabling more accurate process control, increased consumable utility, and possible defectivity reduction.

Agglomeration of gibbsite particles from carbonation process of sodium aluminate solution

The particle size distribution of the carbonation products from sodium aluminate solution was analysed based on the relative mass supersaturation and the particle number conversion from the Malvern volume distribution curves. An approximate relationship was developed which showed that the rate of change of particle number in each particle size interval (0–20 μm, 20–45 μm and 45 μm–∞) per unit volume was proportional to the rate of change of the relative mass supersaturation of the solution. The evolution of agglomeration of gibbsite particles in the carbonation process was also studied and the results show that the agglomeration rate constant is mainly influenced by the initial particle number of gibbsite Al(OH) 3 under the experimental conditions. The agglomeration between fine grains (< 20 μm) plays a dominant role when the initial particle number is large, while the agglomeration between relatively coarse particles (20–45 μm) occurs with a small initial particle number. A carbonation product with extremely narrow-sized distribution and ideal large average size of 75 μm was produced by regulating the relative mass supersaturation of the solution, the amount and particle size distribution of added seeds and other carbonation parameters such as temperature and stirring rate.

Radiopaque iodinated copolymeric nanoparticles for X-ray imaging applications

Recently we described iodinated homopolymeric radiopaque nanoparticles of 28.9 ± 6.3 nm dry diameter synthesized by emulsion polymerization of 2-methacryloyloxyethyl(2,3,5-triiodobenzoate) (MAOETIB). The nanoparticle aqueous dispersion, however, was not stable and tended to agglomerate, particularly at weight concentration of dispersed nanoparticles above ∼0.3%. The agglomeration rate increases as the concentration of nanoparticles in aqueous phase rises and prevents the potential in vivo use as contrast agent for medical X-ray imaging. Here we describe efforts to overcome this limitation by synthesis of iodinated copolymeric nanoparticles of 25.5 ± 4.2 nm dry diameter, by emulsion copolymerization of the monomer, MAOETIB, with a low concentration of glycidyl methacrylate (GMA). The surface of resulting copolymeric nanoparticles is far more hydrophilic than that of polyMAOETIB (PMAOETIB) nanoparticles. Therefore, P(MAOETIB-GMA) nanoparticles are significantly more stable against agglomeration in aqueous continuous phase. After intravenous injection of P(MAOETIB-GMA) nanoparticles in rats and mice (including those with a liver cancer model) CT-imaging revealed a significant enhanced visibility of the blood pool for 30 min after injection. Later, lymph nodes, liver and spleen strongly enhanced due to nanoparticle uptake by the reticuloendothelial system. This favorably enabled the differentiation of cancerous from healthy liver tissue and suggests our particles for tumor imaging in liver and lymph nodes.

Nanoparticle characteristics affecting environmental fate and transport through soil

Nanoparticles are being used in broad range of applications; therefore, these materials probably will enter the environment during their life cycle. The objective of the present study is to identify changes in properties of nanoparticles released into the environment with a case study on aluminum nanoparticles. Aluminum nanoparticles commonly are used in energetic formulations and may be released into the environment during their handling and use. To evaluate the transport of aluminum nanoparticles, it is necessary not only to understand the properties of the aluminum in its initial state but also to determine how the nanoparticle properties will change when exposed to relevant environmental conditions. Transport measurements were conducted with a soil-column system that delivers a constant upflow of a suspension of nanoparticles to a soil column and monitors the concentration, size, agglomeration state, and charge of the particles in the eluent. The type of solution and surface functionalization had a marked effect on the charge, stability, and agglomeration state of the nanoparticles, which in turn impacted transport through the receiving matrix. Transport also is dependent on the size of the nanoparticles, although it is the agglomerate size, not the primary size, that is correlated with transportability. Electrostatically induced binding events of positively charged aluminum nanoparticles to the soil matrix were greater than those for negatively charged aluminum nanoparticles. Many factors influence the transport of nanoparticles in the environment, but size, charge, and agglomeration rate of nanoparticles in the transport medium are predictive of nanoparticle mobility in soil.

Effect of Copper CMP Slurry Chemistry on the Rate of Agglomeration of Alumina Particles

The rate of agglomeration was measured for alumina particles with and without the copper in KNO3 at various pH values. For solutions without copper, agglomeration was greatest at pH of 7.5, near the isoelectric point of 6.5, at a rate of 82 nm/min, following a reaction-limited mechanism. Solutions with a pH away from the isoelectric point underwent reversible agglomeration, reaching a small agglomerate size at steady-state. The addition of copper did not affect agglomeration at pH 4. However, an increase in the agglomeration rates at pH 7.5 and 10 was observed with copper in the solutions, following a diffusion-limited mechanism.

Effect of Copper CMP Slurry Chemistry on the Rate of Agglomeration of Alumina Particles

not Available.

Kinetics of Primary Nanoparticle Agglomeration in Precipitation of Silver

AbstractThe precipitation kinetics of silver was studied using a lab‐scale batch crystallizer with special attention to characterization of agglomeration of primary nanoparticles. The vessel was operated at different feed concentrations, molar ratios, and stirrer speed. Nucleation, volume average crystal growth rates, and agglomeration kernels were determined. Empirical relations were obtained between the rates of the different crystallization steps with supersaturation, magma density, and energy dissipation rate. The results show that larger crystals will be obtained at high supersaturation due to dominance of agglomeration, because the rate of agglomeration also increases with supersaturation, thereby suppressing the primary nucleation rate and enhancing the observed average volume growth rate.

Initial rates of aggregation for dilute, granular flows of wet particles

Molecular dynamics (MD) simulations are used to determine the agglomeration rates of wet grains (particles coated with a viscous, liquid layer) engaged in simple shear flow under dilute conditions. In this work, a closed-form model derived from the elastohydrodynamic theory describes the normal restitution coefficient for binary collisions. Unlike previous MD studies, the particle deformation is not assumed to depend on a particle “overlap” (penetration), but instead depends on the formal coupling of Hertzian deformation theory with lubrication theory. The initial rate of doublet formation is studied as a function of system properties and the energy input to the system. In addition to the system properties, the distribution of relative velocities in the system is found to be a key factor influencing the initial rates of clustering. A theory based on estimating the collision frequency and the critical velocity below which no rebound is observed—due to viscous dissipation—is found to provide a good approximation of the initial aggregation rate. The rate of aggregation is found to increase with increasing number of particles in the system, increasing solid fraction, decreasing overall Stokes number, and decreasing compliance parameter.

Short-term changes in drug agglomeration within interactive mixtures following blending

The objective was to investigate the nature and extent of short-term dynamic changes to dissolution within specific interactive mixtures following blending. Two micronized drugs, nitrazepam and flunitrazepam, were formulated into lactose-based interactive mixtures containing a micronized surfactant. The dissolution rate of the drugs decreased significantly over a period of days after preparation. The dissolution was modelled using a multi-exponential equation, allowing estimation of agglomeration and dissolution rate. From this model, decreasing dissolution rates were consistent with increasing agglomeration. Particle-sizing studies provided evidence of an increase in drug agglomerates over the same timescale. This is the first study to report short-term dissolution changes immediately following secondary processing. Several hypotheses are proposed for increases in agglomeration, which potentially relate to changes in surface charge, particle rearrangements, recrystallisation at surfaces and the role of moisture, although the role of mechanical processing on agglomerate behaviour remains poorly understood. The observations from this study may have wider implications, for dissolution and for other powder-based drug delivery systems which include interactive mixtures with fine powders. This study emphasizes the need for improved understanding if we are to implement a “Quality by Design” ethos to improve control and risk management over the performance and stability of these systems.

Ranking the Lacunary (Bu4N)9{H[α2-P2W17O61]} Polyoxometalate’s Stabilizing Ability for Ir(0)n Nanocluster Formation and Stabilization Using the Five-Criteria Method Plus Necessary Control Experiments

The primary goal of the present studies is to rank the monoprotonated, lacunary Wells-Dawson-type polyoxometalate [H[alpha2-P2W17O61]](9-) as a stabilizing anion for the formation and subsequent stabilization of Ir(0)(n) nanoclusters in acetone using the five-criteria method developed previously ( Ozkar , S. ; Finke , R. G. J. Am. Chem. Soc. 2002 , 124, 5796 ). A related goal is to compare this potentially tetradentate, three W-O(-) plus one W-OH ligand [H[alpha2-P2W17O61]](9-) system to the nanocluster formation and stabilization abilities of the present "gold standard" polyoxometalate, [P2W15Nb3O62]9-, with its established tridentate, three Nb-O-Nb ligating system. A comprehensive table of 54 references at present examining polyoxometalates (POMs) as additives/stabilizers of nanoclusters is also provided as Table S1 of the Supporting Information . To accomplish the above-noted two main goals, the organic-solvent-soluble tetrabutylammonium salts, (Bu4N)8.4[H1.6[alpha2-P2W17O61]] x 1.4H2O, (Bu4N)9[H[alpha2-P2W17O61]], and (Bu4N)9[P2W15Nb3O62] were prepared and their basic structures (by IR) and purity (by 31P NMR, plus elemental analysis where appropriate) were determined. The parent Wells-Dawson POM (Bu4N)6[alpha-P2W18O62] was also prepared, characterized, and then used as a control of a polyoxometalate with little surface anionic charge density, one therefore expected to be a poor stabilizer for at least metal(0)(n), overall neutral core, nanoclusters. Also prepared and characterized was (Bu4N)4[H3[PW11O39]], but its attempted deprotonation by (Bu4N)OH with direct 31P NMR monitoring did not yield a clean product by 31P NMR, so studies with this second lacunary POM were deemphasized. The resultant POMs of known composition, protonation state, and thus overall charge were then evaluated by the five criteriathe one presently available methodfor their ability to promote the kinetically controlled formation, stabilization, and subsequent catalytic activity of prototype Ir(0)(n) nanoclusters. A number of additional control experiments necessary to provide confidence in the results are also reported. One main finding is that the efficacy of the POMs studied herein, as stabilizers for Ir(0)(n) nanoclusters in acetone solvent, is [P2W15Nb3O62]9- > [H[alpha2-P2W17O61]]9- >> [alpha-P2W18O62]6- approximately [H3[PW11O39]]4-, the potentially tetradentate, lacunary [H[alpha2-P2W17O61]]9-proving somewhat less efficacious as a stabilizer than the tridentate Nb-O-Nb containing [P2W15Nb3O62]9-POM. Another finding is that the degree of protonation and the overall charge of the POM matter, the more highly charged [H[alpha2-P2W17O61]]9- POM being a better stabilizer then the more protonated, less charged [H2[alpha2-P2W17O61]]8-. Two additional important findings are better insights into the inherent errors underlying three of the five criteria, and thus the use of the five-criteria method itself, and further evidence supporting the hypothesis that future studies of direct measurements of nanocluster agglomeration rate constants k3 and k4 ( Ott , L. S. ; Finke , R. G. Chem. Mater. 2008 , 20, 2592 - 2601 ) should prove valuable.

Agglomeration and sedimentation of TiO 2 nanoparticles in cell culture medium

The physicochemical characterization of nanoparticles in suspension is a prerequisite for the adequate assessment of their potential biological effect. Little is known to date about the colloidal stability of TiO 2 nanoparticles in cell culture medium. This study investigates the effect of particle concentration, ionic strength, pH, and the presence of fetal bovine serum (FBS) and human serum albumin (HSA) on the colloidal stability of TiO 2 nanoparticles in RPMI cell culture medium, by sedimentation measurements, dynamic light scattering, and electrokinetic measurements ( ζ-potential). TEM revealed that the particles were polydisperse, with diameters ranging from ∼15 to ∼350 nm. The agglomeration rate and sedimentation rate increased with particles’ concentration. The size of the agglomerates at 100 mg/L TiO 2 was significantly reduced, from 1620 ± 160 to 348 ± 13 and 378 ± 15 nm, upon the addition of 10% (v/v) FBS and 1% (w/w) HSA, respectively. The isoelectric point of TiO 2 in water was 2.9 and the measured ζ-potential in RPMI was −16 ± 2 mV at pH 7.4. A slight increase in the ζ-potential of TiO 2 in RPMI was observed upon the addition of FBS and HSA. The addition of FBS and HSA prevented high agglomeration, leading to a stable dispersion of TiO 2 nanoparticles for at least 24 h, possibly due to steric stabilization of the particles.