Particle Formation Conditions Research Articles

Characterization of excipient enhanced growth (EEG) tobramycin dry powder aerosol formulations.

Spray drying can be utilized to produce highly dispersible powder aerosol formulations. However, these formulations are known to be hygroscopic, leading to potential solid-state stability and aerosol performance issues. This study aims to investigate if control of the spray drying particle formation conditions could be employed to improve the solid-state stability and alter the aerosol performance of tobramycin EEG formulations. Eight formulations were prepared, each had the same drug:excipient ratio of 60%w/w tobramycin, 20% w/w l-leucine, 18% w/w mannitol, and 2% w/w poloxamer 188. An experimental design matrix was performed with drying air water content of 1 or 10g/m3 and spray drying solution l-leucine concentrations of 4.6, 7.6, 15.2 or 23.0mmol/L. The particle size, morphology and crystallinity of spray dried formulations were characterized together with their dynamic moisture vapor sorption and aerosol performance. Higher crystallization and glass transition %RH were observed for the formulations spray dried using drying air with higher water content indicating more stable characteristics. Initial screening using a handheld dry powder inhaler of the realistic aerosol performance revealed that neither changing l-leucine concentration nor the drying gas water content affect the in-vitro expected lung dose. However, using a novel positive pressure inhaler, formulations produced using spray drying solutions with lower l-leucine concentrations showed better aerosol performance with MMAD around 2µm and FPF<5µm around 80%.

Effect of deposition conditions on the thermal stability of Ge layers on SiO2 and their dewetting behavior

Resonant light scattering properties of dielectric particles are highly sensitive to particle shapes and optical parameters of particle/substrate systems. To obtain submicron-sized Ge particle arrays of interest for applications in the near-infrared spectral range, we studied the breakup of relatively thick (60 nm) Ge layers on SiO2 caused by dewetting. It was found that the mechanism of the dewetting process depends on the temperature and the method of initial Ge layer deposition. The Ge layers, deposited using a Knudsen cell, were transformed into Ge particles by solid-state dewetting. The particle shape was determined by the kinetics of surface processes. The particle formation from Ge layers, grown by the Ge evaporation using an electron beam, requires their melting. The Ge droplet solidification on SiO2 after the liquid-state dewetting creates the particles of identical shapes close to the hemisperical, indicating that they are formed in the near equlibrium conditions. The scattering magnitude of contact angles reflects the deviation degree of the particle formation conditions from the thermodynamically equilibrium.

H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and particle production in a photolytic flow reactor: chemical modeling, cluster thermodynamics and contamination issues

Abstract. Size distributions of particles formed from sulfuric acid (H2SO4) and water vapor in a photolytic flow reactor (PhoFR) were measured with a nanoparticle mobility sizing system. Experiments with added ammonia and dimethylamine were also performed. H2SO4(g) was synthesized from HONO, sulfur dioxide and water vapor, initiating OH oxidation by HONO photolysis. Experiments were performed at 296 K over a range of sulfuric acid production levels and for 16 % to 82 % relative humidity. Measured distributions generally had a large-particle mode that was roughly lognormal; mean diameters ranged from 3 to 12 nm and widths (lnσ) were ∼0.3. Particle formation conditions were stable over many months. Addition of single-digit pmol mol−1 mixing ratios of dimethylamine led to very large increases in particle number density. Particles produced with ammonia, even at 2000 pmol mol−1, showed that NH3 is a much less effective nucleator than dimethylamine. A two-dimensional simulation of particle formation in PhoFR is also presented that starts with gas-phase photolytic production of H2SO4, followed by kinetic formation of molecular clusters and their decomposition, which is determined by their thermodynamics. Comparisons with model predictions of the experimental result's dependency on HONO and water vapor concentrations yield phenomenological cluster thermodynamics and help delineate the effects of potential contaminants. The added-base simulations and experimental results provide support for previously published dimethylamine–H2SO4 cluster thermodynamics and provide a phenomenological set of ammonia–sulfuric acid thermodynamics.

Estimation of particles emissions from a jet engine in real flight

The article presents the results of particles measurements from a jet engine. Engine parameters were analysed during the actual flight and an attempt was made to map it in stationary tests. Research results were supported by correlation analysis. Based on measurements of particulate matter it was found that the most favourable conditions for particle formation occur during taxiing. Mass distributions were presented and emission factors were determined for three basic phases: taxiing, take-off and approach. The applied research methodology was based on the latest guidelines and was expanded to include propositions related to the analysis of engine operation in real flight conditions.

Aerosol particle formation in the Lithuanian hemi-boreal forest

Aerosol particle observations are needed to determine the conditions of particle formation and growth in different environments. This research focuses on new particle formation (NPF) events in the hemi-boreal forest environment at the Aukštaitija Integrated Monitoring Station (IMS) (55°26ʹN and 26°04ʹE, 170 m above the sea level). The parameterisation of aerosol particle Nucleation I (3–10 nm), Nucleation II (10–20 nm) and Aitken (20–100 nm) modes was performed, their inputs to the total particle number concentration (PNC) and distribution were assessed. It has been estimated that around 40% of days in spring and 22% in summer were NPF event days. The highest contribution of Nucleation mode I aerosol particles was observed in June, reaching up to 38% of the total PNC values. The mean growth rate (GR) and condensation sink (CS) values at the Aukštaitija IMS in April and May were 2.9 nm·h–1, 1.30·10–3 s–1 and 5.3 nm·h–1, 1.35·10–3 s–1, respectively. The GR and CS values were well in agreement with the results obtained from other hemi-boreal forest sites in the Baltic Sea region.

Microfluidic synthesis of metal oxide nanoparticles via the nonaqueous method

Microfluidic synthesis allows for a good control of the particle formation conditions while minimizing the consumption of material. In this study, we exploited these advantages for the nonaqueous synthesis of TiO2, ZnO and CeO2 nanoparticles in a closed micro droplet reactor which resulted in well-defined particle structures. Monodisperse droplets are generated in amicrofluidic flow-focusing area and subsequently transported to a reaction zone allowing synthesis temperatures of up to 200 °C. In addition, we showed that a continuous particle generation process using solid precursor species can be realized without channel clogging. We present different microfluidic designs with reaction zones consisting either of a long meandering channel or a short expansion channel to realize the different reaction times required for the respective model systems. Interestingly, we found that at elevated temperatures, the reaction mixture diffuses into the surrounding continuous phase fluid which leads to a shrinkage of the droplets, forcing eventually the assembly of highly spherical aggregate structures. Depending on the different model systems, we obtained nanospheres of about 100 nm from the CeO2 synthesis and microspheres up to 17 µm in size from the TiO2 synthesis. In contrast, ZnO syntheses at milder temperatures were conducted without any droplet shrinkage which resulted in randomly shaped aggregates of 150 nm that self-assembled in the droplet micro reactor. Thus, a versatile synthesis technique is presented that can be applied for various metal oxides over a broad range of reaction parameters, as a promising approach for the controlled production of high quality nanoparticles.

Particle count and black carbon measurements at schools in Las Vegas, NV and in the greater Salt Lake City, UT area

ABSTRACTAs part of two separate studies aimed to characterize ambient pollutant concentrations at schools in urban areas, we compare black carbon and particle count measurements at Adcock Elementary in Las Vegas, NV (April–June 2013), and Hunter High School in the West Valley City area of greater Salt Lake City, UT (February 2012). Both schools are in urban environments, but Adcock Elementary is next to the U.S. 95 freeway. Black carbon (BC) concentrations were 13% higher at Adcock compared to Hunter, while particle count concentrations were 60% higher. When wind speeds were low—less than 2 m/sec—both BC and particle count concentrations were significantly higher at Adcock, while concentrations at Hunter did not have as strong a variation with wind speed. When wind speeds were less than 2 m/sec, emissions from the adjacent freeway greatly affected concentrations at Adcock, regardless of wind direction. At both sites, BC and particle count concentrations peaked in the morning during commute hours. At Adcock, particle count also peaked during midday or early afternoon, when BC was low and conditions were conducive to new particle formation. While this midday peak occurred at Adcock on roughly 45% of the measured days, it occurred on only about 25% of the days at Hunter, since conditions for particle formation (higher solar radiation, lower wind speeds, lower relative humidity) were more conducive at Adcock. Thus, children attending these schools are likely to be exposed to pollution peaks during school drop-off in the morning, when BC and particle count concentrations peak, and often again during lunchtime recess when particle count peaks again.Implications: Particle count concentrations at two schools were shown to typically be independent of BC or other pollutants. At a school in close proximity to a major freeway, particle count concentrations were high during the midday and when wind speeds were low, regardless of wind direction, showing a large area of effect from roadway emissions even when the school was not downwind of the roadway. At the second school, which sits in an urban neighborhood away from freeways, high particle counts occurred even though solar radiation was low during wintertime conditions, meaning that exposure to high particle counts can occur throughout the year.

Spatially resolved near infrared observations of Enceladus’ tiger stripe eruptions from Cassini VIMS

Particle properties of individual fissure eruptions within Enceladus’ plume have been analyzed using high spatial resolution Visible and Infrared Mapping Spectrometer (VIMS) observations from the Cassini mission. To first order, the spectra of the materials emerging from Cairo, Baghdad and Damascus sulci are very similar, with a strong absorption band around 3µm due to water-ice. The band minimum position indicates that the ice grains emerging from all the fissures are predominantly crystalline, which implies that the water-ice particles’ formation temperatures are likely above 130K. However, there is also evidence for subtle variations in the material emerging from the different source fissures. Variations in the spectral slope between 1–2.5µm are observed and probably reflect differences in the size distributions of particles between 0.5 and 5µm in radius. We also note variations in the shape of the 3µm water-ice absorption band, which are consistent with differences in the relative abundance of > 5µm particles. These differences in the particle size distribution likely reflect variations in the particle formation conditions and/or their transport within the fissures. These observations therefore provide strong motivation for detailed modeling to help place important constraints on the diversity of the sub-surface environmental conditions at the geologically active south-pole of Enceladus.

Nanopatterning Gold by Templated Solid State Dewetting on the Silica Warp and Weft of Diatoms

The diatom,Nitzschia palea, exhibits complex silica shell (frustule) topography that resembles the warp and weft pattern of woven glass. The surface is perforated with a rhombic lattice of roughly oblong pores between periodically undulating transverse weft costae. Exfoliated frustules can be used to template gold nanoparticles by thermally induced dewetting of thin gold films. Acting as templates for the process, the frustules give rise to two coexisting hierarchies of particle sizes and patterned distributions of nanoparticles. By examining temperature dependent dewetting of 5, 10, and 15 nm Au films for various annealing times, we establish conditions for particle formation and patterning. The 5 nm film gives distributions of small particles randomly distributed over the surface and multiple particles at the rhombic lattice points in the pores. Thicker films yield larger faceted particles on the surface and particles that exhibit shapes that are roughly conformal with the shape of the pore container. The pores and costae are sources of curvature instabilities in the film that lead to mass transport of gold and selective accumulation in the weft valleys and pores. We suggest that, with respect to dewetting, the frustule comprises 2-dimensional sublattices of trapping sites. The pattern of dewetting is radically altered by interposing a self-assembled molecular adhesive of mercaptopropyltrimethoxysilane between the Au film overlayer and the frustule. By adjusting the interfacial energy in this manner, a fractal-like overlay of Au islands coexists with a periodic distribution of nanoparticles in the pores.

Cellulose Nanocrystals Obtained from Rice By‐Products and Their Binding Potential to Metallic Ions

The present study aimed to develop and optimize a method to obtain cellulose nanocrystals from the agricultural by‐products rice husk and straw and to evaluate their electrostructural modifications in the presence of metallic ions. First, different particle formation conditions and routes were tested and analyzed by spectrophotometry, dynamic light scattering (DLS), and Zeta potential measurements. Then, electrostructural effects of ions Na(I), Cd(II), and Al(III) on the optimized nanoparticles were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical conductivity (EC) assessments. The produced cellulose nanocrystals adopted a rod‐like shape. AFM height distribution and EC data indicated that the nanocrystals have more affinity in binding with Na(I) &gt; Al(III) &gt; Cd(II). These data suggest that the use of these cellulose nanocrystals in the bioremediation field is promising, both in metal sorption from wastewater and as an alternative for water desalination.

Experimental study of carbon and iron nanoparticle vaporisation under pulse laser heating

The process of vaporisation of carbon and iron nanoparticles induced by a nanosecond Nd:YAG laser pulse at a wavelength of 1,064 nm was investigated. A drop of a volume fraction of both types of particles after the YAG laser pulse was observed by laser light extinction at a wavelength of 633 nm. The nanoparticle sizes and peak particle temperature were measured by the two-colour time-resolved laser-induced incandescence technique. The dependences of the evaporated part of the particle volume fraction and peak particle temperature on laser fluence, particle size and particle formation conditions have been analysed for the carbon and iron nanoparticles. It was found that the process of carbon nanoparticle vaporisation depended on their size and structure, which varied in different formation conditions. It was assumed that the difference in vaporisation process of iron nanoparticles from the bulk was caused by the change of their size and surface tension leading to higher vapour pressure. It is shown that an equilibrium description of nanoparticle vaporisation in laser-induced incandescence model is not valid at high laser fluence and an essential correction of the description of the vaporisation process is necessary.

Structure and properties of core-shell microparticles in paraffin-ultradispersed polytetrafluoroethylene systems

Microsized spherical core-shell particles consisting of hydrocarbon cores encapsulated into fluoropolymer shells are obtained in supercritical carbon dioxide. Paraffins serve as a core material, while the polymer shell is formed from ultradispersed polytetrafluoroethylene. The morphology and molecular structure in the bulk and on the surface of the particles and the influence of conditions of particle formation on the shell thickness and the thermal properties of the materials are studied. The materials are composites comprised of paraffin cores coated with shells of loosened globular fluoropolymer particles with sizes of 0.2–1.7 μm. The shells is built of low- and high-molecular-mass fractions consisting of CF3(CF2)nCF3 molecular chains with different lengths. The shell thickness is governed by preparation conditions, exposure time, and the percentage of the polymer in the initial dispersion.

Phase formation of Mn-doped zinc silicate in water at high-temperatures and high-pressures

Phase formation of Mn-doped zinc silicate (Zn 2SiO 4:Mn 2+, ZSM) in high-temperature and high-pressure water was studied by in situ observations with a hydrothermal diamond anvil cell (HDAC). Precursor was prepared with zinc oxalate dihydrate, manganese oxalate, and silica, where the Zn/Mn/Si molar ratio was 192/8/120 to 199/1/120. Conditions of particle formation were at temperatures up to 650 °C and at pressures up to 1250 MPa. Precursors dissolved at temperatures of 145–203 °C and needle-like particles formed through homogeneous nucleation at temperatures from 357 to 374 °C, close to the critical point of water. The needle-like particles grew at growth rates of 0.5–3.8 μm/s and were identified to be ZSM as evident from their green luminescence. ZSM synthesized in supercritical water (400 °C for 180 min) by batch reactions had comparable luminescence with that of ZSM produced by solid-state reaction (1200 °C for 240 min) using the same precursor. The key finding in this work is that the precursors can be made to dissolve in near-critical water and that this allows ZSM to form via a homogeneous nucleation process.

Stöber silica particle size effect on the hardness and brittleness of silica monoliths

Micro-indentation experiments were performed on monoliths prepared by drying dispersions of Stöber silica nano-sized particles in the 15–115 nm diameter range. Monolith hardness and resistance to fracture change gradually: the monoliths made with the smaller particles have smoother surfaces and resist to higher indentation forces while the monoliths made out of the larger particles are very brittle. These differences are assigned to changes in particle microchemistry associated to the differences in particle sizes, evidenced in a previous work from this group: larger particles are more extensively cross-linked and thus less plastic than smaller particles. This is in turn due to a larger amount of non-hydrolyzed ethoxy groups in the smaller particles, which limits the extent of cross-linking and creates domains containing linear siloxane chains that contribute to mechanical energy dissipation and thus to increased monolith tenacity and decreased hardness. Optical and electron microscopy examination of monolith surfaces show a large number of defects at different scales on the monoliths formed by larger particles. Under high magnification in a field-emission scanning electron microscope, larger particles appear less deformed and less densely packed than the smaller particles, thus contributing to lower cohesion energy. These results show a clear connection between the conditions for particle formation, their chemical and morphological features and the resulting mechanical properties of macroscopic solids.

Infrared spectroscopy of acetic acid and formic acid aerosols: pure and compound acid/ice particles

Acetic acid aerosol particles, formic acid aerosol particles and mixed acid/ice particles were generated in a collisional cooling cell at a temperature of 78 K and investigated using in situ rapid scan Fourier transform infrared spectroscopy. The infrared spectra reveal that the internal structure of the particles critically depends on the particle formation conditions and, especially for the mixed particles, on the composition. The acetic acid particles are likely to have only a partially crystalline structure whereas the formic acid particles are likely to have an overall crystalline structure. The existence of acid in the mixed acid/ice particles prevents the ice from crystallization even at low acid concentrations (less than 10%). Mid-infrared refractive index data were derived from the different particle spectra, which can be helpful for remote sensing of such systems.

Size effects in the infrared spectra of NH3 ice nanoparticles studied by a combined molecular dynamics and vibrational exciton approach

Infrared extinction spectra of ammonia ice nanoparticles with radii between 2 and 10 nm show pronounced band shape variations depending on the conditions of particle formation by collisional cooling. We present experimental and theoretical evidence showing that the variations in the region of the nu2 (umbrella) fundamental are due to changes in the particle size. The effect is analyzed in terms of an explicit atomistic model of the particles' structure and vibrational dynamics. An explicit potential function combined with a novel extension of the vibrational exciton approach allows us to simulate extinction spectra for particles containing up to 16,000 atoms. It is shown that the particles formed under the conditions of our experiments consist of a crystalline core surrounded by an amorphous shell with an approximately constant thickness of 1-2 nm. For the nu2 fundamental, this shell gives rise to a broad band [full width at half maximum (FWHM) 72 cm(-1)] blueshifted by about 19 cm(-1) relative to a narrow peak (FWHM of 19 cm(-1)) which arises from the crystalline core.

New particle formation observed in the tropical/subtropical cirrus clouds

Previous studies show that new particle formation takes place in the outflows of marine stratus and cumulus clouds. Here we show measurements of high concentrations of ultrafine particles, diameters (Dp) from 4 to 9 nm (N4–9), in interstitial cloud aerosol. These ultrafine particles indicate that in situ new particle formation occurs interstitially in cirrus clouds. Measurements were made at altitudes from 7 to 16 km over Florida with instruments on the WB‐57F aircraft during Cirrus Regional Study of Tropical Anvils and Cirrus Layers‐Florida Area Cirrus Experiments (CRYSTAL‐FACE) in July 2002. Size‐resolved ice crystal particle concentrations and water vapor concentrations were measured to help identify the presence of cirrus clouds. About 72% of the in‐cloud samples showed new particle formation events with the average N4–9 of 3.0 × 103 cm−3, whereas about 56% of the out‐of‐cloud samples had events with the lower N4–9 of 1.3 × 103 cm−3. The periods during which high N4–9 appeared were often associated with times of increasing ice water content (IWC) and high relative humidity with respect to ice (RHI); however, the measured N4–9 was not quantitatively correlated to IWC. The magnitude and frequency of new particle formation events seen in cirrus clouds were also higher than those previously observed in the tropical/subtropical upper troposphere in the absence of clouds. These results suggest that cirrus clouds may provide favorable conditions for particle formation, such as low temperatures, high RHI, high OH production (due to high water vapor), cloud electricity, and atmospheric convection. At present, however, particle formation mechanisms in clouds are unidentified.

Formation of silver particles and periodicprecipitate layers in silicate glass induced by thermally assistedhydrogen permeation

Nanoscale silver particles embedded in sodium silicate glass wereproduced by Na/Ag ion exchange and subsequent thermal treatment in ahydrogen atmosphere. Their structure and spatial distribution werestudied by conventional and high-resolution electron microscopy(HREM). Two different mechanisms of particle formation could beidentified: (i) reduction of ionic silver by hydrogen and formationof mostly defective particles (twinned) within a near-surfaceregion; and (ii) formation of single-crystalline particles in theinterior of the glass resulting from reduction by means ofpolyvalent iron ions. Electron microscopy investigation revealedthe completion of periodic layers of silver particles innear-surface regions with high silver concentration induced bythermally assisted hydrogen permeation. The self-organized periodiclayer formation may be explained in terms of Ostwald'ssupersaturation theory, assuming interdiffusion of two mobilespecies. Analysis of lattice plane spacings from HREM images ofsilver particles revealed the typical size-dependent latticecontraction. The extent of this, however, was found to be differentfor particles formed by hydrogen permeation and those formed byinteraction with polyvalent iron ions. These differences reflectdifferent influences of the surrounding glass matrix, probablyoriginating from the conditions of particle formation (thermal history).

Thermal Stabilization and Crystallization of Nanometric Particles of Si-C-N Produced by RF-Plasma Enhanced Chemical-Vapor-Deposition

ABSTRACTNanoparticles of Si-alloys were grown at room temperature in a RF-PECVD process from mixtures of SiH4, CH4 and NH3. Quasi-monodisperse nanoparticles were produced in conditions of fast particle development. Among the different conditions for particle formation, we chose moderate low pressure (below 100Pa) and RF-power lower than 200W in all cases. The particle size was controlled through the modulation of the RF power supplied to the discharge. A post-thermal treatment at 800-900°C was used to eliminate the hydrogen of the particles and to stabilize them against environmental oxidation. To study the thermal crystallization of the particles, various thermal-treatments were used. The annealing of these particles at 1400°C for one hour under Ar or N2 led to different results depending on the composition of the samples as revealed by HRTEM and electron-diffraction analysis: SiC particles showed a marked internal crystallization; SiCN particles developed nanocrystals embedded in their amorphous matrix; Si particles crystallized in diamond-like silicon when annealed in Ar, whereas long whiskers of the α-Si3N4 phase, 50-200nm wide, grew from the particles in N2.

Control of the pore characteristics of thin alumina membranes with ultrafine zirconia particles prepared by the reversed micelle method

Ultrafine zirconia particles were prepared by hydrolysis of zirconium tetrabutoxide in micro water pools of reversed micelles formed with a novel surfactant, dioleyl phosphoric acid. By repeating a dipping-firing cycle, the mesopores of a γ-alumina membrane were packed with the zirconia particles. The gas permeability of the membrane was dependent on the conditions of particle formation and calcination. The former affected the size of the zirconia particles, and the latter influenced the removal of carbonaceous matters and the sintering of the particles. The permselectivity of hydrogen to nitrogen increased with repetition of the impregnation cycle, and exceeded a value of 4.5 after six cycles, the initial value being 3.4. The membrane was stable up to at least 800 K.