Primary Particle Diameter Research Articles

Transmission electron microscopy (TEM) as a tool for identification of combustion products: application to black layers in speleothems

The present study deals with the application of High Resolution Transmission Electron Microscopy (HRTEM) to dark layers, occurring in the speleothems of Domica Cave (Slovakia). Chemical pre-treatment was necessary for sample purification and the effective extraction of carbon soot. For purposes of comparison, soot aggregates obtained from laboratory experiments on the combustion of beech wood and collected from a diesel engine also were studied. HRTEM analyses of combustion products permit a distinction to be made between soot aggregates that originated in different combustion processes. The diameter of spherical, primary particles depends on the conditions of combustion, notably temperature. Burning in diesel engines produces soot with relatively small, primary particles (diameter d p = 34 ± 4 nm). Primary, spherical particles of soot aggregates, obtained from the combustion of beech wood, were larger (diameter d p = 42 ± 5 nm). The diameters of primary particles of soot separated from Domica flowstones (samples DOM1 and DOM2) were similar to the wood samples (d p = 50 ± 9 nm). Another type of carbonaceous particle, obtained in the combustion process, had a spherical shape, but the diameter of about 50–500 nm was significantly larger than that of soot. Analyses performed on two samples (DOM S1 and DOM S2) confirmed that the black laminae owed their colour to particles, formed during wood combustion and later retained in the speleothems.

Combined optical and TEM investigations for a detailed characterization of soot aggregate properties in a laminar coflow diffusion flame

In order to develop soot models that include effects due to particle aggregation, data must be obtained from flames containing all of the relevant chemical and physical processes that affect the evolution of a soot particle. In this study, the effective radius of gyration of aggregated soot is experimentally determined in nitrogen-diluted ethylene coflow diffusion flames using 2-D multi-angle light scattering (2D-MALS). High spatial resolution is achieved by minimizing signal blur that results from imaging light scattering from the probe volume at oblique angles. The results are validated at six locations in the flame through comparison to an effective radius of gyration derived from transmission electron microscope (TEM) analysis of thermophoretically-sampled soot. Simulations are used to model the path taken by a soot particle to reach the TEM grid to ensure the sampling measurements have the spatial resolution necessary to differentiate between aggregate properties at different radial locations in the flame. A radial distance δ is determined from which the front face of the probe is offset from the desired sample location. The ability of the probe to separately capture wing and centerline soot morphology is confirmed by comparison to a previous time-resolved laser-induced incandescence (TiRe-LII) measurement of primary particle diameter. The observed increase in polydispersity and maximum diameter of primary particles along the flame wing compared to the centerline is thought to be a result of surface growth. Excellent agreement is found between the effective radius of gyration derived from 2D-MALS and TEM analysis. The TEM results not only confirm the optical measurement but also elucidate the effective radius of gyration, which depends on aggregate size and polydispersity.

Multimethod approach for the detection and characterisation of food-grade synthetic amorphous silica nanoparticles

Synthetic amorphous silica (SAS) has been used as food additive under the code E551 for decades and the agrifood sector is considered a main exposure vector for humans and environment. However, there is still a lack of detailed methodologies for the determination of SAS’ particle size and concentration. This work presents the detection and characterization of NPs in eleven different food-grade SAS samples, following a reasoned and detailed sequential methodology. Dynamic Light Scattering (DLS), Multiangle Light Scattering (MALS), Asymmetric Flow-Field Flow Fractionation (AF4), Inductively Coupled Plasma Mass Spectrometry (ICPMS) and Transmission Electron Microscopy (TEM) were used. The suitability and limitations, information derived from each type of analytical technique and implications related to current EC Regulation 1169/2011 on the provision of food information to consumers are deeply discussed. In general the z-average, AF4 hydrodynamic diameters and root mean square (rms) radii measured were in good agreement. AF4-ICPMS coupling and pre channel calibration with silica NPs standards allowed the reliable detection of NPs below 100nm for ten of eleven samples (AF4 diameters between 20.6 and 39.8nm) and to quantify the mass concentration in seven different samples (at mgL−1 concentration level). TEM characterisation included the determination of the minimum detectable size and subsequent measurement of the equivalent circle diameter (ECD) of primary particles and small aggregates, which were between 10.3 and 20.3nm. Because of the dynamic size application range is limited by the minimum detectable size, all the techniques in this work can be used only as positive tests.

Improved sizing of soot primary particles using mass-mobility measurements

ABSTRACTThe properties and impacts of aggregated aerosol particles (i.e., soot, metal oxide fumes) depend on their morphology, as characterized by fractal dimension, prefactor, and primary particle diameter. The morphology may be measured directly by time-consuming ex situ microscopy or rapid but indirect in situ methods. Previously, it was found that particle mass and mobility measurements could be used for the estimation of the primary particle diameter of zirconia aggregates, using plausible assumptions related to the fractal structure (specifically, prefactor and exponent ). Since the formation and growth of zirconia aggregates are different from carbon soot, here we compare primary particle diameters measured directly from transmission electron microscopy analysis of soot particles with the diameters estimated from mass–mobility measurements. Performing extensive measurements on soot emissions from two reciprocating engines over a range of operating conditions, we found that there are no universal va...

Morphology, chemical composition and nanostructure of single carbon-rich particles studied by transmission electron microscopy: source apportionment in workroom air of aluminium smelters.

Sources of C-rich particles at work places in two aluminium smelters in Norway were studied by transmission electron microscopy and energy-dispersive X-ray microanalysis. Based on morphology, nanostructure and chemistry, three different types of C-rich particles are distinguished: (a) chain-like agglomerates (70-100% by number, relative to the sum of C-rich particles) consisting of primary particles with typical onion-shell structure of graphene layers, (b) multi-walled carbon nanotube particles (≈3%) and (c) spheres or agglomerates of amorphous C-rich particles (0-30%). Chain-like agglomerates are interpreted as diesel soot in accordance with literature data on primary particle diameter, chemical composition and nanostructure of primary particles. The source of the observed multi-walled carbon nanotubes is not known. The amorphous C-rich particles most likely consist of organic carbon species which cannot be characterized further by X-ray microanalysis. Unaltered graphitic electrode material was not found among the C-rich particles. The high fraction of diesel soot particles indicates that elemental carbon is generally suited as proxy for diesel soot in aluminium smelters. However, due to the presence of carbon nanotubes and amorphous C-rich particles, detailed characterization of sources of carbon-rich particles by electron microscopy is recommended for accurate assessment of adverse health effects.

Effect of Drive Cycle and Gasoline Particulate Filter on the Size and Morphology of Soot Particles Emitted from a Gasoline-Direct-Injection Vehicle.

The size and morphology of particulate matter emitted from a light-duty gasoline-direct-injection (GDI) vehicle, over the FTP-75 and US06 transient drive cycles, have been characterized by transmission-electron-microscope (TEM) image analysis. To investigate the impact of gasoline particulate filters on particulate-matter emission, the results for the stock-GDI vehicle, that is, the vehicle in its original configuration, have been compared to the results for the same vehicle equipped with a catalyzed gasoline particulate filter (GPF). The stock-GDI vehicle emits graphitized fractal-like aggregates over all driving conditions. The mean projected area-equivalent diameter of these aggregates is in the 78.4-88.4 nm range and the mean diameter of primary particles varies between 24.6 and 26.6 nm. Post-GPF particles emitted over the US06 cycle appear to have an amorphous structure, and a large number of nucleation-mode particles, depicted as low-contrast ultrafine droplets, are observed in TEM images. This indicates the emission of a substantial amount of semivolatile material during the US06 cycle, most likely generated by the incomplete combustion of accumulated soot in the GPF during regeneration. The size of primary particles and soot aggregates does not vary significantly by implementing the GPF over the FTP-75 cycle; however, particles emitted by the GPF-equipped vehicle over the US06 cycle are about 20% larger than those emitted by the stock-GDI vehicle. This may be attributed to condensation of large amounts of organic material on soot aggregates. High-contrast spots, most likely solid nonvolatile cores, are observed within many of the nucleation-mode particles emitted over the US06 cycle by the GPF-equipped vehicle. These cores are either generated inside the engine or depict incipient soot particles which are partially carbonized in the exhaust line. The effect of drive cycle and the GPF on the fractal parameters of particles, such as fractal dimension and fractal prefactor, is insignificant.

Smoke Production and Fractal Structure Properties of Soot from n-Heptane Pool Fires Under Low Pressures

The purpose of this work is to investigate the influence of low air pressure on the smoke production and fractal structure properties of soot aerosols formed in fires. A series of experiments of n-heptane pool fires were conducted in a pressure chamber that could simulate ambient pressures from 40.4 kPa to 101 kPa. Soot aerosols were collected by carbon-supported copper grids and then examined by scanning electron microscopy to determine the soot morphology. A smoke meter was employed to detect the extinction coefficient of smoke in the chamber. The results indicate that the mean primary particle diameter, the mean number of primary particles per aggregate and the mean aggregate radius of gyration were reduced with decreasing air pressure. The Mueller matrix element S11 and extinction efficiency factor were calculated using the discrete dipole approximation method. For the soot formed at lower pressure, values of S11 of the overall scattering angles are much less than those formed under higher pressure. The scattering asymmetry factors indicate that forward scattering is dominant for soot particles of n-heptane pool fires. The ratio of forward scattering intensity to backward scattering intensity along with the extinction efficiency factor of single soot particle and the extinction coefficient of smoke decrease with decreasing pressure; the mean extinction coefficient of smoke is proportional to pressure to the power 3.3. These results may be useful for engineers to develop smoke detectors or other related technologies applied in cargo compartments or other regions under low pressure.

On the radiative properties of soot aggregates – Part 2: Effects of coating

The effects of weakly absorbing material coating on soot have attracted considerable research attention in recent years due to the significant influence of such coating on soot radiative properties and the large differences predicted by different numerical models. Soot aggregates were first numerically generated using the diffusion limited cluster aggregation algorithm to produce fractal aggregates formed by log-normally distributed polydisperse spherical primary particles in point-touch. These aggregates were then processed by adding a certain amount of primary particle overlapping and necking to simulate the soot morphology observed from transmission electron microscopy images. After this process, a layer of WAM coating of different thicknesses was added to these more realistic soot aggregates. The radiative properties of these coated soot aggregates over the spectral range of 266–1064nm were calculated by the discrete dipole approximation (DDA) using the spectrally dependent refractive index of soot for four aggregates containing Np=1, 20, 51 and 96 primary particles. The considered coating thicknesses range from 0% (no coating) up to 100% coating in terms of the primary particle diameter. Coating enhances both the particle absorption and scattering cross sections, with much stronger enhancement to the scattering one, as well as the asymmetry factor and the single scattering albedo. The absorption enhancement is stronger in the UV than in the visible and the near infrared. The simple corrections to the Rayleigh–Debye–Gans fractal aggregates theory for uncoated soot aggregates are found not working for coated soot aggregates. The core–shell model significantly overestimates the absorption enhancement by coating in the visible and the near infrared compared to the DDA results of the coated soot particle. Treating an externally coated soot aggregate as an aggregate formed by individually coated primary particles significantly underestimates the absorption enhancement by coating in the visible and the near infrared.

Particle Emission Characteristics of a Gas Turbine with a Double Annular Combustor

The total climate, air quality, and health impact of aircraft black carbon (BC) emissions depend on quantity (mass and number concentration) as well as morphology (fractal dimension and surface area) of emitted BC aggregates. This study examines multiple BC emission metrics from a gas turbine with a double annular combustor, CFM56-5B4-2P. As a part of the SAMPLE III.2 campaign, concurrent measurements of particle mobility, particle mass, particle number concentration, and mass concentration, as well as collection of transmission electron microscopy (TEM) samples, allowed for characterization of the BC emissions. Mass- and number-based emission indices were strongly influenced by thrust setting during pilot combustion and ranged from <1 to 208 mg/kg-fuel and 3 ×× 1012 to 3 ×× 1016 particles/kg-fuel, respectively. Mobility measurements indicated that mean diameters ranged from 7 to 44 nm with a strong dependence on thrust during pilot-only combustion. Using aggregation and sintering theory with empirical effective density relationships, a power-law relationship between primary particle diameter and mobility diameter is presented. Mean primary particle diameter ranged from 6 to 19 nm; however, laser-induced incandescence (LII) and mass-mobility-calculated primary particle diameters demonstrated opposite trends with thrust setting. Similarly, mass-mobility-calculated aggregate mass specific surface area and LII-measured surface area were not in agreement, indicating both methods need further development and validation before use as quantitative indicators of primary particle diameter and mass-specific surface area.Copyright 2015 American Association for Aerosol Research

Aggregate characteristics accounting for the evolving fractal-like structure during coagulation and sintering

Coagulation and partial coalescence (or sintering) frequently results in fractal-like aerosol structures in natural and industrial processes. The asymptotic form of such structures is described reasonably well with the so-called fractal dimension, Df. Little is known, however, for its evolution, from spheres to fractal-like particles and, in particular, its effect on aerosol primary particle and collision diameters that determine the environmental impact or manufactured product performance. So the effect of a variable or constant Df on product crystalline (TiO2) and amorphous (SiO2) aerosol particle characteristics is elucidated over their process synthesis parameter space ( maximum temperature 1600–2000K, cooling rate 103–106K/s and precursor molar fraction 10−4–10−1). Aerosol dynamics by coagulation and sintering are simulated accounting for the evolving fractal-like structure by either a linear interpolation or detailed mesoscale simulations from spherical to asymptotic fractal-like structures. In addition, two sintering rates for SiO2 as well as expressions for the effect of particle structure on sintering rate are compared in terms of product particle characteristics. Neglecting the evolution of Df hardly affects the product primary particle and soft-agglomerate diameters but overestimates the agglomerate collision diameter growth rate during the hard- to soft-agglomerate transition. This underpredicts the hard-agglomerate diameter by 25–30% at high cooling rates (105–106K/s).

Ultrafine particulate matter formation in the early stage of pulverized coal combustion of high-sodium lignite

Abstract In this work, the pulverized coal combustion of Zhundong lignite was conducted in an optically-accessible, downward Hencken flat-flame burner to investigate the incipient formation of ultrafine particulate matter (PM). The ultrafine PM were collected in - flame from distinct positions under 1800 K, 1500 K and 1200 K using a self-designed thermophoretic sampler, together with extensive conventional transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS) examinations. A novel in situ low-intensity phase-selective laser-induced breakdown spectroscopy (PS-LIBS) was further introduced to diagnose the dynamic behavior of particle-phase sodium during the pulverized coal combustion. The primary particles in the collected ultrafine PM have mean diameter of 8–15 nm, with Si and Na as main mineral components based on TEM/HRTEM–EDS results. The formation of ultrafine PM is regarded as a process of multi-component flame syntheses of mineral precursors, in which the competition between the devolatilization and the coalescence of particles are of most significance. Finally, based on an approach of time scale analysis, three characteristic times of minimum mean diameter of primary particles, the initial increment point of particle-phase sodium and the maximum devolatilization are found to be highly correlated.

Characteristics of airborne gold aggregates generated by spark discharge and high temperature evaporation furnace: Mass–mobility relationship and surface area

The properties of gas-borne aggregates are important in nano-technology and for potential health effects.Gold aggregates from three generators (one commercial and one custom built spark discharge generator and one high-temperature furnace) have been characterized. The aggregate surface areas were determined using five approaches – based on aggregation theory and/or measured aggregate properties. The characterization included mass-mobility relationships, effective densities (assessed by an Aerosol Particles Mass analyzer), primary particle analysis (based on Transmission Electron Microscopy), as well as total mass and number concentration outputs.The relationships between mass and mobility are well described by power-law functions with exponents of 2.18–2.35. For all generators, the primary particles of the aggregates were fused together by a bridge with a diameter typically ~60–70% of the primary particle diameter (5–10 nm). The total mass outputs were 6.1–48.1 mg/m3 and the predicted surface area outputs in the range 0.9×10-3–17×10-3 cm2/cm3.The aggregate effective densities differed considerably between generators. The difference could partly be explained by the differences in primary particle diameter, but not fully. This in turn may be explained either by a varying primary particle size with aggregate size, or by that there are slight differences in the morphology of the aggregates from the generators.

A simple semi-empirical model for effective density measurements of fractal aggregates

Effective density measurements are used extensively to convert submicron particle sizes based on a particle׳s mobility diameter into mass. Measurements of the effective density also provide information concerning the particle morphology. For example, the effective density curves of fractal aggregates reveal a scaling factor that seems to correlate with the fractal dimension of the particles. The present paper proposes a simple semi-empirical model that permits the quantitative interpretation of these measurements to determine parameters such as the fractal dimension, the primary particle size, and the bulk density of an aggregate particle. The proposed model is based on the assumption that the hydrodynamic drag force of an aggregate is proportional to the drag force applied to isolated primary spheres and to the number of primary spheres in the aggregate at power α. The model was applied to soot particles produced by either a spark discharge (PALAS GFG1000) or by combustion (miniCAST 5206)—both mechanisms enable the generation of aggregates or agglomerates with very different primary sphere diameters. The proposed model showed a good fit for all of the effective density measurements obtained in this study; the α parameter was driven by the aggregate fractal dimension and by the Knudsen number that was determined based on the primary particle diameter. Finally, for a known primary particle diameter, the fractal dimension and the bulk density were determined successfully with the proposed model.

A green synthesis of bis[1-(hydroxy-κO)-2(1H)-pyridinethionato-κS2]-(T-4)-zinc (zinc pyrithione) nanoparticles via mechanochemical milling

Particulate bis[1-(hydroxy-κO)-2(1H)-pyridinethionato-κS2]-(T-4)-zinc (zinc pyrithione; ZPT) in the diameter range 0.5–0.7 µm is a US FDA-approved anti-dandruff active widely used in anti-dandruff shampoos. A nanoparticulate form of ZPT is expected to exhibit a higher activity, be distributed more effectively on the scalp, require less thickening agent in the shampoo formulation to ensure its stability against settling than the standard form of ZPT, and would enable clear anti-dandruff shampoo formulations. We demonstrate, for the first time, that a green, mechanochemical nanoparticle synthesis process can be used to prepare nanoparticulate ZPT from zinc chloride and sodium pyrithione monohydrate. Both a Reeves attrition mill and a Retsch MixerMill were found to be effective tools for delivering the mechanical energy needed for the conversion. The infrared spectra and X-ray powder diffraction patterns for the products correspond to those for the known desired material. Transmission electron microscopic analysis indicates that ZPT nanoparticles with primary particle diameters in the range of 20–200 nm (mean diameters of 65–100 nm) can be obtained via this method.

Structural evolution of soot particles during diesel combustion in a single-cylinder light-duty engine

The structural evolution of soot particles in a single-cylinder, light-duty diesel engine has been investigated by conducting thermophoretic soot sampling and subsequent transmission electron microscope (TEM) imaging. The location of TEM grid with respect to a diesel flame is varied so that soot particles are sampled at three different combustion stages including (1) when the impingement of flame on the wall occurs, (2) after the flame impingement, and (3) during the late-cycle burn-out. For comparison purposes, engine-out soot particles are also collected at the same operating conditions. The results show that diesel soot particles are aggregates of varying numbers of primary particles. It is found that the flame impingement on the wall makes a significant impact on the soot aggregate structures, evidenced by the decreased mean radius of gyration of the aggregates from 38 to 26nm between the wall-impinging and post-impingement stages. This was due primarily to the fragmentation of large soot aggregates while the mean diameter of primary particles remains the same. From the post-impingement to late-cycle burn-out stages, most of the soot aggregates disappear due to the oxidation leaving only highly agglomerated substructures. As a result, soot aggregates show higher fractal dimension in the late-cycle burn-out stage than that in the previous stages. The intensive soot oxidation also reduces primary particle diameter from 19 to 15nm through surface oxidation. The engine-out soot samples show similar particle size and structure to the late-cycle samples, suggesting that the late-cycle soot particles experienced little oxidation before exiting through the exhaust. This leads to a conclusion that the highly agglomerated substructures of soot aggregates can survive the late-cycle burn-out and become a major contributor to exhaust soot emissions.

Formation mechanisms of soot from high-molecular-weight polycyclic aromatic hydrocarbons

The feedstocks, including benzene, acetylene, and benzene with acetylene or 2–7 ring PAH, were pyrolyzed in an isothermal laminar flow at 1400–1650K. The particle size distributions (PSDs) of soot and nascent soot were analyzed using a scanning mobility particle sizer (SMPS). The morphology of particles with the same mobility particle diameter was examined using a scanning electron microscope (SEM), where the grid was sampled via thermophoretic sampling assisted by a differential mobility analyzer (DMA). The soot produced by the pyrolysis of acetylene at 1400K exhibited the highest number concentration and a log-normal distribution compared with those of the soot produced by the pyrolysis of benzene and the PAH additives. At 1500K, the pyrolysis of PAHs with three or more rings with zigzag sites significantly increased the number concentration, although the added carbon concentration was smaller than that of acetylene. The addition of dibenzo[a,e]pyrene, which possesses three armchair sites, inhibited soot formation, suggesting that the bay site is easily formed and that the formation of anisotropic PAHs inhibits dimerization. The morphology of the soot formed by the addition of dibenzo[a,e]pyrene exhibited a primary particle diameter of 10nm and similar primary particles, whereas the morphology of the soot formed by the addition of PAHs with zigzag sites clearly indicated a structure with a primary particle diameter of 20–40nm. These observations indicate that the incipient soot is formed by the formation of dimers or small clusters of large PAHs via the mechanisms of aromatic molecule addition to aromatic radicals referred to as the PAH–addition cyclization (PAH–AC) mechanism at high temperatures, whereas moderate-sized PAHs developed via the hydrogen-abstraction–carbon-addition (HACA) mechanism form clusters and incipient soot at relatively low temperatures.

Measurements and modeling of laser-induced incandescence of soot at different heights in a flat premixed flame

Laser-induced incandescence (LII) measurements were conducted in a laminar flat rich premixed CH4/O2/N2 flame at atmospheric pressure using a Nd:YAG laser operated at 1,064 nm. Time-resolved LII signals were measured at 610 nm (20 nm FWHM) at different heights above the burner exit surface and at different laser fluences. The averaged soot temperature over 10 ns around the laser peak was determined from spectrally resolved LII signals over the spectral range of 500–630 nm. Flame temperature and soot primary particle diameter and aggregate size at several flame heights were obtained using the NO-LIF thermometry and from image analyses of sampled soot. The time-resolved LII signal and the averaged soot temperature were modeled using two LII models. To achieve reasonable agreement between the modeled and experimental LII signal and soot temperature at low laser fluences, it is necessary to use flame height-dependent soot absorption functions. Such practice can be attributed to the continuous variation of soot thermal and/or radiative properties during the surface growth process after inception. At high laser fluences, both LII models are unable to reproduce the overall shape of the normalized time-resolved LII signal profiles and the averaged soot temperatures.

The electrical mobilities and scalar friction factors of modest-to-high aspect ratio particles in the transition regime

In this work, we compared measured electrical mobilities of spherical and non-spherical nanoparticles to the predictions of both transition regime and free molecular theories. Mobility measurements were performed using a differential mobility analyzer (DMA) with both air and carbon dioxide as background gases, at atmospheric pressure and room temperature. For all measurements, DMA operational settings were selected in an attempt to minimize particle alignment with the electric field or flow direction, such that particles traversed the DMA rotating close to randomly. The particles included gold nanospheres (diameters of 50nm and 70nm), polystyrene latex dimers (primary particle diameter of 116nm), gold nanorods (mobility equivalent diameters of 40–70nm; aspect ratio 1.8–14) and carbon nanotubes (mobility equivalent diameters of 48.3nm –60.3nm; aspect ratios 9.5–243). Our primary objective was to test the accuracy of a transition regime theory (Dahneke’s adjusted sphere model) for non-spherical particles; this theory suggests that electrical mobilities are dependent upon a particle Knudsen number, specifically defined as Kn=λπRH/PA, where λ is the background gas mean free path, RH is the particle’s hydrodynamic radius, and PA is its projected area. For this test, electrical mobilities were calculated from the dimensions of particles collected downstream of a DMA and observed via TEM, with the DMA operated with fixed voltage and sheath flowrate. Mobility calculations for each particle were used to reconstruct electrical mobility histograms, which we show are directly comparable to the DMA transfer function for the operating conditions selected. We further compared the mean electrical mobilities of electrical mobility ranked sub-populations to the transfer function weighted mean mobilities of “windows” smaller in width than the DMA transfer function. Through analysis we find that in the 0.7<Kn<6 range, measurements are explained well by the proposed transition regime expression (the adjusted sphere model), with transfer function weighted and sub-population mean electrical mobilities typically within 10% of one another. Electrical mobilities calculated using solely free molecular models were in reasonable agreement with observations (±20%) for Kn>3, but were systematically lower (by up to 50%) than measurements for 1<Kn<3. Based upon the presented measurements and analysis, we propose that (1) an appropriate Knudsen number-dependent friction factor/electrical mobility expression needs to be used in interpreting DMA measurements not only for spheres (as is common practice), but also non-spherical nanorods and nanotubes, and (2) the expression tested here is suitable for such measurement interpretation.

Air Entrainment During Flame Aerosol Synthesis of Nanoparticles

Enclosed flames typically produce substantially larger particles than open flames under identical reactant flows and composition. The enclosure hinders air entrainment to the flame and reduces heat losses by radiation and convection, facilitating particle coagulation and coalescence. Here the effect of natural air entrainment on flame aerosol synthesis is investigated by lifting off the enclosing tube from the burner surface and utilizing tracer gas (Ne) analysis after calibration with forced air entrainment. That way the effect of air entrainment on product primary particle diameter and mobility size distribution dynamics is investigated by microscopy, scanning mobility particle sizing, and N2 adsorption, while temperature is measured by Fourier-transform infrared spectroscopy. So air entrainment during flame spray pyrolysis is examined here for its versatility in scalable manufacture of an array of material compositions, while copper oxide (CuO) is used for its electro-chemical applications (e.g., batte...

Impact of nanoparticle aggregation on protein recovery through a pentadentate chelate ligand on magnetic carriers.

The growing need for more efficient separation techniques still dominates downstream processing of biomolecules, thus encouraging the continuous development of advanced nanomaterials. In this paper we present an improved process for recovering recombinant histidine tagged green fluorescent protein from an E. coli cell lysate. Superparamagnetic core-shell nanocarriers are functionalized with a pentadentate chelate affinity ligand and then loaded with metal ions (Cu(2+), Ni(2+), or Zn(2+)). The separation process yields high binding capacity (250 mg/g), good selectivity, purity >98%, good recyclability with 90% capacity after 9 cycles, and long-term stability. We determined the main physical properties of the magnetite-based nanoparticles such as saturation magnetization (59 A m(2)/kg), primary particle diameter (22 ± 4 nm), and specific surface area (89 m(2)/g). Our results show that this material is a promising tool for bioseparation applications. One special focus of the work includes analyzing the changes in the hydrodynamic size distribution using dynamic light scattering and transmission electron microscopy. We relate these effects to different interaction levels in the system and discuss how the stronger aggregation of the magnetite core is the main limiting factor for the separation yield, leading to a considerable decrease in the number of metal ions available for biomolecular capture. Otherwise weaker interactions lead instead to agglomeration effects that have no impact on the binding capacity of the system. The simple relation between the size of the aggregated units and the size of the primary particles corresponds approximately to the relation between the number of existing binding sites and the actual protein binding in the separation process. Compared with that, the effect of steric hindrance among proteins is of less significance.