Submicron-sized Particles Research Articles

Impact of the coagulation of dust particles on Mars during the 2018 global dust storm

Coagulation of particles occurs when two particles collide and stick together. In the Martian atmosphere, coagulation of dust would increase the dust effective particle size, as small particles accrete to larger particles. Murphy et al. (1990) concluded that Brownian coagulation of dust in the Martian atmosphere was not significant, due to the low dust particle mixing ratios, while Montmessin et al. (2002) and Fedorova et al. (2014) showed that it mostly involves dust particle radii smaller than 0.1 μm. However, the effects of coagulation have never been explored in 3D, during a global dust storm, and in presence of larger numbers of small particles. Here we revisit this issue by using the NASA Ames Mars Global Climate Model (MGCM) to investigate the temporal and spatial changes in dust particle sizes during the 2018 global dust storm due to dust coagulation and the overall impact of these processes on Mars' climate. Our parameterization for dust coagulation includes the effect of Brownian motion, Brownian diffusion enhancement, and gravitational collection. We show that Brownian motion and Brownian diffusion enhancement dominate gravitational collection. Coagulation has a significant impact during the global storm, with coagulation rates increased by a factor of 10 compared to non-storm conditions. The mean effective particle radius can be increased by a factor of up to 2 due to coagulation, leading to a 20 K colder atmosphere above 30 km altitude. Overall, our parameterization improves the representation of the decay phase of the storm relative to MCS dust observations. Coagulation also remains a significant process affecting dust outside the storm period if large numbers of submicron-sized particles are involved. As coagulation removes the small sub-micron particles within a relatively short time, it may therefore be possible, in GCMs, to lift larger amounts of submicron-sized particles from the surface without excess dust buildup in the atmosphere, thus improving the agreement with some of the observations without diverging from the observed column opacities.

A portable flow tube homogenizer for aerosol mixing in the sub-micrometre and lower micrometre particle size range

A portable and light-weight aerosol homogenizer has been designed and validated experimentally. The design relies on large-scale primary standards for particle number and mass concentration previously developed for metrology applications, but the dimensions have been scaled down to produce a versatile and user-friendly apparatus for everyday applications in aerosol sciences. The homogenizer is a 0.8 m long cylinder made of steel with an inner diameter of 50 mm, equipped with three inlets for primary aerosols and up to four outlets for sampling homogenized aerosol mixtures. Mixing is achieved by three turbulent air jets. The aerosol spatial homogeneity in the sampling zone was within ±1% and ±4% for 2 and 5 µm polystyrene (PS) particles, respectively. The possibility to supply and control independently aerosol flows with pressure-sensitive generators and the short equilibration time (<1 min) have also been demonstrated. The homogenizer allows for mixing various aerosol components, such as soot, inorganic species and mineral dust particles, to generate ambient-like aerosols in the laboratory or industrially manufactured particles such as PS spheres as model aerosols. We believe that it could have applications in applied aerosol research, health-related studies, and instrument calibration.

3DED in situ single-crystal studies on submicron-sized particles during redox reactions in gas environments and electrochemical reactions

3DED <i>in situ</i> single-crystal studies on submicron-sized particles during redox reactions in gas environments and electrochemical reactions

Submicron-size polystyrene modulates amyloid fibril formation: From the perspective of protein corona

At present, nanoplastics have been detected in food and the environment, but they have serious impacts on the human body. As one of the typical representatives of nanoplastics, polystyrene (PS) is generally used as an experimental object. Few studies found that PS could modulate the formation of amyloid fibrils, leading to the occurrence of diseases. However, its submicron-scale effects remain elusive. Thus, this study aimed to explore the interaction between PS of particle size 100–500 nm and hen egg-white lysozyme (HEWL). The results showed that PS of size 400 nm markedly promoted the primary nucleation step of amyloid fibril formation, and fibrils had more small fragments compared with PS of size 100 nm in the control and sample groups. PS of larger particle size changed the spatial structure of HEWL significantly. This study analyzed the experimental results from the perspective of protein corona and thermodynamics. The study confirmed that PS was able to form protein corona with HEWL in the initial stage, which was mainly driven by hydrophobic interactions. More importantly, the interface and junction of the protein corona were the main sites for the formation of amyloid fibrils. This study highlighted the role of submicron particle size and discussed the toxic effects of nanoparticles.

Preparation of PLGA Nanoparticles by Milling Spongelike PLGA Microspheres

Currently, emulsification-templated nanoencapsulation techniques (e.g., nanoprecipitation) have been most frequently used to prepare poly-d,l-lactide-co-glycolide (PLGA) nanoparticles. This study aimed to explore a new top-down process to produce PLGA nanoparticles. The fundamental strategy was to prepare spongelike PLGA microspheres with a highly porous texture and then crush them into submicron-sized particles via wet milling. Therefore, an ethyl formate-based ammonolysis method was developed to encapsulate progesterone into porous PLGA microspheres. Compared to a conventional solvent evaporation process, the ammonolysis technique helped reduce the tendency of drug crystallization and improved drug encapsulation efficiency accordingly (solvent evaporation, 27.6 ± 4.6%; ammonolysis, 65.1 ± 1.7%). Wet milling was performed on the highly porous microspheres with a D50 of 64.8 μm under various milling conditions. The size of the grinding medium was the most crucial factor for our wet milling. Milling using smaller zirconium oxide beads (0.3~1 mm) was simply ineffective. However, when larger beads with diameters of 3 and 5 mm were used, our porous microspheres were ground into submicron-sized particles. The quality of the resultant PLGA nanoparticles was demonstrated by size distribution measurement and field emission scanning electron microscopy. The present top-down process that contrasts with conventional bottom-up approaches might find application in manufacturing drug-loaded PLGA nanoparticles.

Effects of heat treatment and compaction pressure on the microstructure and magnetic properties of core-shell structured FeSiBNbCu/SiO2 soft magnetic composites

Here, the FeSiBNbCu/SiO2 soft magnetic composites (SMCs) with core-shell structure were successfully designed and fabricated using nanocrystalline powders as seeds and SiO2 were grown by sol-gel technique onto the surface of the seed particles. We systematically investigated the influences of annealing temperature and compaction pressure on the micromorphology, chemical structure and soft magnetic properties of the SMCs. The results demonstrate that a large number of submicron-sized SiO2 particles are uniformly deposited on the surface of the powders, which significantly improves the insulating characteristics between the magnetic powders. Also, the effective permeability μe increases and the core loss Pcv decreases with increasing annealing temperature from 480 °C to 550 °C, which is attributed to the relaxation of internal stress and the increase of volume fraction of α-Fe(Si) grains. Furthermore, an increase in compaction pressure effectively increases the densification and reduces the porosity, which facilitates a denser microstructure. Under the combined effect of optimal annealing temperature and compaction pressure, the SMCs exhibit high μe of 84 and low Pcv of 174 kW/m3 at 50 kHz for Bm = 0.1 T. This work provides a new strategy for the construction of core-shell structure and a comprehensive understanding of the relationship between process parameters and microstructure, which is of great guiding significance for industrial production.

Retrieval of the sea spray aerosol mode from submicron particle size distributions and supermicron scattering during LASIC

Abstract. Improved quantification of sea spray aerosol concentration and size is important for determining aerosol effects on clouds and the climate, though attempts to accurately capture the size distribution of the sea spray mode remain limited by the availability of supermicron size distributions. In this work, we introduce a new approach to retrieving lognormal mode fit parameters for a sea spray aerosol mode by combining submicron size distributions with supermicron scattering measurements using a Mie inversion. Submicron size distributions were measured by an ultra-high-sensitivity aerosol spectrometer (UHSAS), and supermicron scattering was taken as the difference between &lt;10 µm and &lt;1 µm three-wavelength integrating nephelometer measurements (NEPH). This UHSAS-NEPH method was applied during background marine periods of the Department of Energy Atmospheric Radiation Measurement Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign on Ascension Island (November 2016–May 2017), when the contribution of sea spray aerosol was expected to represent a large fraction of the aerosol mass and total scattering. Lognormal sea spray modal parameters were retrieved from comparisons between nephelometer measurements and a lookup table of Mie theory-simulated scattering coefficients for low-error solutions that minimized the 0.4–1 µm residual in the UHSAS size distribution. We evaluated the UHSAS-NEPH method with a set of clean marine measurements in the North Atlantic that included supermicron size and chemical measurements, showing that measured supermicron size distributions are needed to constrain the sea spray number concentration but that mass concentration was reasonably characterized using supermicron scattering. For LASIC, the UHSAS-NEPH method retrieved sea spray mode properties for approximately 88 % of the background marine times when the scattering variability and total particle concentration were low (&lt;± 5 Mm−1 and &lt;400 cm−3, respectively), with mass mean diameter ranging from 0.6 to 1.9 µm (1.47 ± 0.17 µm), modal width ranging from 1.1 to 3.97 (2.4±0.3), and mass concentration ranging from 0.18 to 23.0 µg m−3 (8.37. ± 4.1 µg m−3). The measured nephelometer scattering at three wavelengths was found to constrain the mode width marginally at the largest particle sizes in the absence of additional size and chemical measurements for defining parameters for the Mie solutions. Comparing UHSAS-NEPH retrievals to those of a fitting algorithm applied only to the submicron UHSAS number size distribution showed that correlations between retrieved mass concentration and the available mass-based sea spray tracers (coarse scattering, wind speed, and chloride) are low when supermicron measurements are not considered. This work demonstrates the added value of supermicron scattering measurements for retrieving reasonable sea spray mass concentrations, providing the best-available observationally constrained estimate of the sea spray mode properties when supermicron size distribution measurements are not available.

Commercial Janus Fabrics as Reusable Facemask Materials: A Balance of Water Repellency, Filtration Efficiency, Breathability, and Reusability.

Facemasks as personal protective equipment play a significant role in helping prevent the spread of viruses during the COVID-19 pandemic. A desired reusable fabric facemask should strike a balance of water repellency, good filtration efficiency (FE), breathability, and mechanical robustness against washing cycles. Despite significant efforts in testing various commercial fabric materials for filtration efficiency, few have investigated fabric performance as a function of the fiber/yarn morphology and wettability of the fabric itself. In this study, we examine commercial fabrics with Janus-like behaviors to determine the best reusable fabric facemask materials by understanding the roles of morphology, porosity, and wettability of the fabric on its overall performance. We find that the outer layer of the diaper fabric consisted of laminated polyurethane, which is hydrophobic, has low porosity (∼5%) and tightly woven yarn structures, and shows the highest overall FE (up to 54%) in the submicron particle size range (0.03-0.6 μm) among the fabrics tested. Fabric layers with higher porosity lead to lower-pressure drops, indicating higher breathability but lower FE. Tightly woven waterproof rainwear fabrics perform the best after 10 washing cycles, remaining intact morphologically with only a 2-5% drop in the overall FE in the submicron particle size range, whereas other knitted fabric layers become loosened and the laminated polyurethane thin film on the diaper fabric is wrinkled. In comparison, the surgical masks and N95 respirators made from nonwoven polypropylene (PP) fibers see over a 30% decline in the overall FE after 10 washing cycles. Overall, we find that tightly woven Janus fabrics consisting of a low porosity, a hydrophobic outer layer, and a high porosity and hydrophilic inner layer offer the best performance among the fabrics tested as they can generate a high overall FE, achieve good breathability, and maintain fabric morphology and performance over multiple washing cycles.

Industrial waste-based submicron additives in cement mortars

Purpose: The aim of this work is the development of materials and technologies, which provide their repeated life cycle. Methodology/approach: Scanning electron microscopy, thermogravimetric analysis, X-ray diffraction analysis. Research findings: The processing method is proposed for fluorocarbon-containing waste (RUSAL, Krasnoyarsk) resulting in the formation of submicron-sized carbon in the form of a coal-water slurry for solution and/or concrete modification. It is shown that carbon in the coal-water slurry represents flat plates with the submicron-sized particles. The degree of cement hydration increases with the addition of wastes, indicating the material strengthening, which is consistent with the results of strength tests. The acicular spike crystals of hydrated calcium silicates become larger and thicker, that confirms the assumption that hydration increases with the addition of submicron-sized carbon particles. Practical implications: The obtained physical and mechanical properties of the cement-sand mortar show the possibility of using the proposed modifiers in the production of materials with high bending strength at early stages to reduce cracking, especially in thin concrete layers with a large coverage area.

Stimulated low-frequency Raman light scattering in systems of nano- and submicron-sized particles

We present a brief review of experimental work on the investigation of stimulated low-frequency Raman scattering of light in systems of submicron and nanosized particles of various physical nature.

Mixed material wear particle isolation from periprosthetic tissue surrounding total joint replacements.

Submicron‐sized wear particles are generally accepted as a potential cause of aseptic loosening when produced in sufficient volumes. With the accelerating use of increasingly wear‐resistant biomaterials, identifying such particles and evaluating their biological response is becoming more challenging. Highly sensitive wear particle isolation methods have been developed but these methods cannot isolate the complete spectrum of particle types present in individual tissue samples. Two established techniques were modified to create one novel method to isolate both high‐ and low‐density materials from periprosthetic tissue samples. Ten total hip replacement and eight total knee replacement tissue samples were processed. All particle types were characterized using high resolution scanning electron microscopy. UHMWPE and a range of high‐density materials were isolated from all tissue samples, including: polymethylmethacrylate, zirconium dioxide, titanium alloy, cobalt chromium alloy and stainless steel. This feasibility study demonstrates the coexistence of mixed particle types in periprosthetic tissues and provides researchers with high‐resolution images of clinically relevant wear particles that could be used as a reference for future in vitro biological response studies.

Low-Temperature Sintering of l-Alanine-Functionalized Metallic Copper Particles Affording Conductive Films with Excellent Oxidative Stability.

Here, the alpha amino acid l-alanine is employed as both a capping and stabilizing agent in the aqueous synthesis of submicron-sized metallic copper particles under ambient atmospheric conditions. The reduction of the copper(II) precursor is achieved using l-ascorbic acid (vitamin C) as the reducing agent. The nature of the complex formed between l-alanine and the copper(II) precursor, pH of the medium, temperature, and the relative proportion of capping agent are found to play a significant role in determining the size, shape, and oxidative stability of the resulting particles. The adsorbed l-alanine is shown to act as a barrier imparting excellent thermal stability to capped copper particles, delaying the onset of temperature-induced aerial oxidation. The stability of the particles is complemented by highly favorable sintering conditions, rendering the formation of conductive copper films at significantly lower temperatures (T ≤ 120 °C) compared to alternative preparation methods. The resulting copper films are well-passivated by residual surface l-alanine molecules, promoting long-term stability without hindering the surface chemistry of the copper film as evidenced by the catalytic activity. Contrary to the popular belief that ligands with long carbon chains are best for providing stability, these findings demonstrate that very small ligands can provide highly effective stability to copper without significantly deteriorating its functionality while facilitating low-temperature sintering, which is a key requirement for emerging flexible electronic applications.

Diffusion separation of submicron particles by using magnetized spheres

The diffusion capture of submicron-sized particles in the gradient field formed by the magnetized ferromagnetic spheres in the external homogeneous magnetic field has been theoretically investigated. Magnetic field measurements were made with a specially designed prototype magnetometer. The simple semi-empirical formula of the magnetic force acting on the submicron particle was determined. The analytical solution of the diffusion equation for steady states was obtained. The concentration distribution of the particles in capturing regions was determined. A formula was obtained to evaluate the critical size of the submicron particles captured in this area. The effects of magnetic, hydrodynamic and geometric parameters of the investigated system on the critical size of the particles in the diffusion event were evaluated. The critical size of the particles decreased with the increase of the external magnetic field and was found to be independent of the dimensions of the spheres. As a result; the diffusion separation phenomenon in the gradient field formed by the magnetized ferromagnetic spheres is more effective than in the gradient magnetic field formed by the wires. The results obtained contribute to the development of the theory of magnetic separators using ferromagnetic matrix elements.

On the dust production of active asteroid (3200) Phaethon in 2009: What the DESTINY+ spaceprobe could encounter

Asteroid (3200) Phaethon is long known to be a parent body of the Geminid meteoroid stream. While replenishment of the Geminid suggests regular emanation of dust from Phaethon, its comet-like activity was first detected only in June of 2009 (Jewitt & Li 2010). We conduct a reexamination of those observations and demonstrate that there were two waves of dust emanation. It is significant that the two temporal maxima of the Phaethon coma brightness were separated by a noticeable dimming of the coma that can be explained by fast departure of the ejected dust particles from the field of view. This rapid motion necessarily constrains size of dust particles to being of a few micrometers or smaller. Under the assumption of submicron-size dust particles, the total volume of the ejected material can be remarkably small, only ∼1 m3 that is a factor of ∼105 smaller compared to what was suggested in Jewitt & Li (2010) and ∼102 smaller compared to that of Jewitt et al. (2013). Such a small ejecta volume can be acquired from a meteoroid with radius of less than 5 cm, striking Phaethon at relative velocity of ≤ 100 km/s. An impact of a series of such small meteoroids on Phaethon when it was ∼0.14 au from the Sun does not seem unrealistic.

Relationship between size and cellulose content of cellulose microgels (CMGs) and their water-in-oil emulsifying capacity

Soluble polysaccharides have been used extensively as gelling/thickening agents in emulsions, but they generally display weak surface activity. Insoluble polysaccharides such as cellulose can be converted to thickening agents and even emulsifiers, but generally only after considerable chemical modification. Here we use the ionic liquid (IL) 1-butyl-3-methyl imidazolium acetate (BmimAc) to dissolve and reprecipitate cellulose in the presence of oil, i.e., a physical process, to tune the cellulose properties. ILs have previously been used in this way to form hydrophobic (‘oily’) cellulose microgels (CMGs), potentially capable of stabilizing water-in-oil (W/O) emulsions. However, these previous CMGs were made via a ‘top-down’ method and were relatively large and polydisperse, giving limited stability to the W/O emulsions formed. Here we demonstrate how the CMG size can be drastically reduced via a ‘bottom-up’ approach and employing high-pressure homogenization (HPH), thus achieving sub-micron CMG particle sizes. This has previously been impossible with other reported IL-cellulose coagulation methods and the corresponding W/O emulsions were more stable. In addition, confocal and cryo-scanning electron microscopy (SEM) revealed that the surface coverage of these CMGs on droplets increased over time, which led to the formation of even thicker interfacial layers and further enhanced emulsion stability (at least 2 months). We also demonstrate unequivocally that the stability of the W/O emulsions is indeed due to the CMGs adsorbing via the Pickering mechanism, rather than forming a stabilizing cellulosic network in the continuous phase, thus providing a novel route to ‘green’ Pickering emulsions.

Colloidal Polydopamine Beads: A Photothermally Active Support for Noble Metal Nanocatalysts

Polydopamine (PDA) is a unique bioinspired synthetic polymer that integrates broadband light absorption, efficient photothermal transduction, and versatile surface-adhesion functions in a single material entity. Here, we utilize colloidal PDA beads in the submicron particle size regime as an easily processable and photothermally active support for sub-10 nm Pd nanocatalysts to construct a multifunctional material system that allows us to kinetically boost thermal catalytic reactions through visible and near-infrared light illuminations. Choosing the Pd-catalyzed nitrophenol reduction by ammonium formate as a model transfer hydrogenation reaction exhibiting temperature-dependent reaction rates, we demonstrate that interfacial molecule-transforming processes on metal nanocatalyst surfaces can be kinetically modulated by harnessing the thermal energy produced through photothermal transduction in the PDA supports.

Rapid removal of PFOA and PFOS via modified industrial solid waste: Mechanisms and influences of water matrices.

Emerging perfluoroalkyl and polyfluoroalkyl substances contaminate waters at trace concentrations, thus rapid and selective adsorbents are pivotal to mitigate the consequent energy-intensive and time-consuming issues in remediation. In this study, coal combustion residuals-fly ash was modified (FA-SCA) to overcome the universal trade-off between high adsorption capacity and fast kinetics. FA-SCA presented rapid adsorption (teq = 2 min) of PFOX (perfluorooctanoic acid and perfluorooctanesulfonic acid, collectively), where the dynamic adsorption capacity (qdyn = qm/teq) was 2-3 orders of magnitude higher than that of benchmark activated carbons and anion-exchange resins. Investigated by advanced characterization and kinetic models, the fast kinetics and superior qdyn are attributed to (1) elevated external diffusion driven by the submicron particle size; (2) enhanced intraparticle diffusion caused by the developed mesoporous structure (Vmeso/Vmicro = 8.1); (3) numerous quaternary ammonium anion-exchange sites (840 μmol/g), and (4) appropriate adsorption affinity (0.031 L/μmol for PFOS, and 0.023 L/μmol for PFOA). Since the adsorption was proven to be a synergistic process of electrostatic and hydrophobic interactions, effective adsorption ([PFOX]ini = 1.21 μM, concentration levels of highly-contaminant-sites) was obtained at conventional natural water chemistries. High selectivity (>85.4% removal) was also achieved with organic/inorganic competitors, especially compounds with partly similar molecular structures to PFOX. In addition, >90% PFOX was removed consistently during five cycles in mild regeneration conditions (pH 12 and 50 °C). Overall, FA-SCA showed no leaching issues of toxic metals and exhibits great potential in both single-adsorption processes and treatment train systems.

Deagglomeration of spray-dried submicron particles by low-power aqueous sonication

The resistance to deagglomeration of spray-dried agglomerated particles of submicron size was investigated using an ultrasonication system in water. Submicron agglomerates consisting of water-insoluble primary particles with size of 10 or 100 nm were prepared in different shapes by varying the heating profile during spray drying. Deagglomeration experiments were performed using a low-power sonication device. Spherical agglomerates were found to be more resistant to ultrasonic forces, while dent- or doughnut-shaped agglomerates tended to break down. The results show that the shape of the agglomerate plays an important role in the energy balance of the ultrasound operation. The energy produced from the collapse of cavitation bubbles in the ultrasound vessel may be used to promote motion of the agglomerates and deagglomeration.

Microstructure and tensile properties of in-situ synthesized and hot-extruded aluminum-matrix composites reinforced with hybrid submicron-sized ceramic particles

Aluminum-matrix composites (AMCs) reinforced with submicron-sized ceramic particles of Al2O3, TiB2 and TiC were in-situ synthesized by reactive sintering of Al, TiO2, and B4C powder mixtures and further densified by hot-extrusion process. The reaction mechanisms for formation of the reinforcing particles, extrusion behavior, microstructure, and tensile properties of the AMCs have been investigated. The reactions of TiO2 and B4C with molten Al were a stepwise process, and there were many intermediate phases including oxygen deficient titanium oxides (Ti3O5, Ti2O3, and TiO), Al4C3, AlB2, and Al3Ti, before the expected reinforcing particles of Al2O3, TiB2, and TiC were formed. The results showed that hot-extrusion process was an effective means to densify reactive-sintered porous composites, and dense AMCs can be obtained through hot-extrusion in a temperature range of 480–550°C. The microstructure of the resulting AMCs was characterized by fine reinforcing ceramic phases with an average particle size of 0.24 μm, which were homogeneously distributed in Al matrix. Furthermore, no significant change in particle sizes could be found after extrusion, and ceramic particle content and extrusion temperature have small influences on the average particle sizes of the reinforcing phases. The presence of these sub-micron hybrid ceramic particles resulted in significant enhancements in yield and tensile strength of the AMCs. The yield strength improvement is mostly due to the coefficient of thermal expansion (CTE) mismatch between the ceramic particles and Al matrix, followed by Orowan strengthening, while the relative contributions of grain refinement and load-bearing effects are much smaller.

Magnetization process of cubic Fe3O4 submicron particles studied by polarized small-angle neutron scattering

We report results of polarized small-angle neutron scattering (SANS) experiments at T = 10 K and 300 K for cubic Fe3O4 submicron-sized particles, where formation of a complex spin vortex is expected. Magnetic SANS intensities of magnetization components in the direction perpendicular and parallel to the magnetic field were observed to change significantly at around the coercivity. Magnetization components parallel to the field minimizes around the coercivity both at T = 10 K and 300 K, whereas those perpendicular to the magnetic field maximizes near the coercivity and the maximum value differ greatly, depending on the temperature. Based on results of micromagnetic simulations, the observed SANS intensities were interpreted as due to magnetic structural changes from a flower to a spin vortex state and gradual tilting of a vortex core from the external field to magnetocrystalline anisotropy axes at low fields.