Particle Growth Mechanism Research Articles

X-Band Radar and Surface-Based Observations of Cold-Season Precipitation in Western Colorado’s Complex Terrain

Abstract Hydrologic processes associated with intermountain cold-season precipitation in the Upper Colorado River basin have important impacts on avalanche forecasting and water resource management. However, traditional weather radar networks struggle with observations in this complex terrain. Data collected during the Study of Precipitation, the Lower Atmosphere, and the Surface for Hydrometeorology (SPLASH) and its sister campaign, Surface Atmosphere Integrated Field Laboratory (SAIL) in the East River watershed of western Colorado, are used to examine a multistorm period from 23 December 2021 to 1 January 2022 that contributed 35% of the total winter precipitation in this watershed. Dual-polarization X-band radar and disdrometer measurements show ∼30-mm differences in precipitation amount at two sites in proximity over four distinct storm events within the period. Wind patterns, synoptic forcings, microphysical characteristics of precipitation, and surface meteorology are analyzed to explain the observed spatial variability of cold-season precipitation in complex mountainous terrain. Analysis shows that differences over time within this event are mainly accounted for by synoptic forcings, such as frontal passages; differences between sites are accounted for by the impact of variations in local wind patterns on precipitation microphysics. Patterns of surface precipitation intensity are compared and found to be correlated with X-band radar signatures; a relationship between a strong dendritic growth stage and intense low-density surface precipitation is reinforced by this study. This relationship demonstrates the importance of particle growth mechanisms on surface snowfall patterns in high-altitude complex terrain, underscoring the importance of realistic microphysical parameterizations. Significance Statement The amount and density of snowpack from western Colorado winter storms have significant impacts on water resources in the Upper Colorado River basin. Snowpack characteristics are affected by small-scale differences in how snow forms in the atmosphere. These differences are hard to study in the complex terrain of the Rockies, but data from the SPLASH and SAIL field campaigns allows us to investigate how snow crystal formation and mountain-driven wind patterns affect snow near the surface. Our study finds that snow crystal growth varies over small space and time scales and is likely controlled by the terrain beneath a given location and resultant local wind patterns. These results imply that predicting snowpack in the Rockies requires properly representing local wind patterns and crystal growth processes in models.

Growth Mechanisms of Amorphous Nanoparticles in Solution and During Heat Drying

The purpose of this study was twofold: to identify the growth mechanisms of amorphous nanoparticles in solution and during the drying process at high temperatures, and to guide the process condition and stabilizer selection for amorphous nanoparticle formulations. In contrast to nanocrystals that are mostly mechanically robust, amorphous nanoparticles tend to undergo deformation under stress. As a result, development of a stable formulation and evaluation of the drying process for re-dispersible amorphous nanoparticles presents considerable challenges. Although amorphous nanoparticles have stability issues, they have several pros in terms of production, high monodispersity, and diverse applications in drug delivery. In this study, amorphous nanoparticles were prepared via liquid-liquid phase separation, and their growth mechanisms were investigated both in solution and during the drying process. In solution, particles were found to be susceptible to flocculation, crystallization, coalescence, and Ostwald ripening, with coalescence being a preliminary step providing the driving force for Ostwald ripening. However, during the heat drying process, coalescence and crystallization were found to be the primary mechanisms for particle growth, with Ostwald ripening being negligible due to reduced molecular mobility. The glass transition temperature (Tg) of these amorphous nanoparticles was found to be a crucial factor both in solution and during the drying process. At temperatures < Tg, particles remained in a rigid, glassy state thereby inhibiting coalescence, whereas at or above Tg, particles transition from glassy to rubbery state, making them more susceptible to deformation and coalescence. The mechanistic understanding of particle growth from this study can also be extended to the stabilization of other types of soft nanoparticles.

From Cauliflowers to Microspheres: Particle Growth Mechanism in Self-Stabilized Precipitation Polymerization.

Self-stabilized precipitation (2SP) polymerization enables the facile synthesis of uniform polymer spheres with sizes ranging from 100 nm to 3 μm, without the need for stabilizers or cross-linkers, even at high monomer concentrations of up to 30%. While previous studies have extensively explored the influence of reaction conditions on the size and uniformity of microsphere products, their impact on particle morphology has received less attention. In this work, we demonstrate that particle growth in 2SP polymerization primarily occurs via the adsorption of polymers from the solution onto the particle surface, leading to an increase in particle circularity and a smoother surface. The surface roughness of the particles is controlled by the aggregation of primary particles and the subsequent polymer adsorption process during the growth stage. Smooth microspheres are obtained under conditions of moderate monomer concentration, high initiator concentration, and elevated temperature. Our findings highlight the significance of the particle growth process in determining particle morphology in addition to the well-established role of polymer-solvent interactions during precipitation polymerization.

Tailoring particle size/morphology for the stable cathode performance of polygonal-shaped Li(Ni,Mn)2O4 single crystals

We regulate the particle size and crystallographic facet of single-crystal (SC) Li(Ni,Mn)2O4 (LNMO) cathode materials via flux-selective molten salt method. By simply adjusting Li2MoO4 or LiI as sintering aids, we synthesized size controlled SC particles, both small and large, and comparatively investigated their electrochemical behavior focusing on the lithiation/delithiation reactivity in conjunction with the particle size and surface planes. Considering the growth mechanism of a SC particles with a specific crystal plane, such particle size control is not determined solely by the synthetic condition but must also consider the interfacial energy of the crystal planes in conjunction with the fluxes what we used. While the initial charge capacity is similar, the given cathode using a small SC LNMO (using LiI) with uniform particle sizes (≤5 μm) exhibits outstanding rate capability with stable capacity retention under changing current density, which indicates stable lithium transport during the repetitive electrochemical reactions. The dependency of the impedance response with change in the electrode resistances as well as the stability during the cycle reactions in conjunction with the post-mortem Li distribution by using laser-induced breakdown spectroscopy as a function of porosity change and cell degradation are thoroughly discussed from the standpoint of regulated particle property.

Do bromine and surface-active substances influence the coastal atmospheric particle growth?

New particle formation (NPF) is considered a major source of aerosol particles and cloud condensation nuclei (CCN); however, our understanding of NPF and the subsequent particle growth mechanisms in coastal areas remains limited. This study provides evidence of frequent NPF events followed by particle growth in the middle Adriatic Sea during the summer months at the coastal station of Rogoznica in Croatia. To our knowledge, this is the first study to report such events in this region. Our research aims to improve the understanding of NPF by investigating particle growth through detailed physicochemical characterization and event classification. We used a combination of online measurements and offline particle collection, followed by a thorough chemical analysis. Our results suggest the role of bromine in the particle growth process and provide evidence for its involvement in combination with organic compounds. In addition, we demonstrated the significant influence of surface-active substances (SAS) on particle growth. NPF and particle growth events have been observed in air masses originating from the Adriatic Sea, which can serve as an important source of volatile organic compounds (VOC). Our study shows an intricate interplay between bromine, organic carbon (OC), and SAS in atmospheric particle growth, contributing to a better understanding of coastal NPF processes. In this context, we also introduced a new approach using the semi-empirical 1st derivative method to determine the growth rate for each time point that is not sensitive to the nonlinear behavior of the particle growth over time. We observed that during NPF and particle growth event days, the OC concentration measured in the ultrafine mode particle fraction was higher compared to non-event days. Moreover, in contrast to non-event days, bromine compounds were detected in the ultrafine mode atmospheric particle fraction on nearly all NPF and particle growth event days. Regarding sulfuric acid, the measured sulfate concentration in the ultrafine mode atmospheric particle fraction on both NPF event and non-event days showed no significant differences. This suggests that sulfuric acid may not be the primary factor influencing the appearance of NPF and the particle growth process in the coastal region of Rogoznica.

Dust-gas coupling in turbulence- and MHD wind-driven protoplanetary disks: Implications for rocky planet formation

The degree of coupling between dust particles and their surrounding gas in protoplanetary disks is quantified by the dimensionless Stokes number. The Stokes number (St) governs particle size and spatial distributions, in turn establishing the dominant mode of planetary accretion in different disk regions. In this paper, we model the characteristic St of particles across time in disks evolving under both turbulent viscosity and magnetohydrodynamic (MHD) disk winds. In both turbulence- and wind-dominated disks, we find that collisional fragmentation is the limiting mechanism of particle growth. The water-ice sublimation line constitutes a critical transition point in dust settling, drift, and size regimes. For a fiducial disk evolution parameter α̃≃10−3, silicate particles inteior to the ice-line are characterized by low St (≲10−2) and sizes in the sub-mm- to 1cm-scale. Icy particles/boulders beyond the ice-line are characterized by high St (≳10−2) and sizes in the cm to dm size range. Hence, icy particles settle into a thin layer at the outer disk midplane and drift inward at velocities exceeding the gaseous accretionary flow due to substantial headwind drag. Silicate particles in the inner disk remain relatively well dispersed and are to a large extent advected inward with their surrounding gas.The St dichotomy across the ice-line translates to distinct planet formation pathways between the inner and outer disk. While pebble accretion proceeds slowly for rocky embryos within the ice-line (across most of parameter space), it does so rapidly for volatile-rich embryos beyond it, allowing for the growth of giant planet cores before disk dissipation. Through simulations of rocky planet growth, we evaluate the competition between pebble accretion and classical pairwise collisions between planetesimals. We conclude that the dominance of pebble accretion can only be realized in disks that are driven by MHD winds, slow-evolving (α̃≲10−3.5), and devoid of pressure maxima that may concentrate solids and give rise of planetesimal rings in which classical growth is enhanced. Such disks are extremely quiescent, with Shakura-Sunyaev turbulence parameters αν≲10−4. We conclude that for most of parameter space corresponding to values of αν reflected in observations of protoplanetary disks (≳10−4), pairwise planetesimal collisions constitute the dominant pathway of rocky planet accretion. Our results are discussed in the context of super-Earth origins, and lend support to the emerging view that they formed in planetesimal rings. Moreover, these results argue against a significant contribution (≳ 10%) of outer disk, carbonaceous material to the proto-Earth in the form of pebbles, in agreement with chemical and isotopic investigations of Earth’s accretion history.

Morphological design of LaTiO2N particles by topotactic growth mechanisms for photocatalytic applications

Solar water-splitting using particle photocatalysts is a promising approach to sustainably produce hydrogen. LaTiO2N is an auspicious visible light absorbing photocatalyst regarding the oxygen evolution reaction. In this work, the topotactic growth mechanism of LaTiO2N particles is investigated by varying the precursor material and the synthesis conditions during thermal ammonolysis. Their influence is discussed in regard to structure, composition, morphology, optical, and functional properties. Using the conventional, layered perovskite oxide, La2Ti2O7, as precursor resulted in brick-shaped porous LaTiO2N particles with a high degree of crystallinity and a high surface area. When adding flux, the increased mobility during thermal ammonolysis leads to larger morphology changes resulting in non-porous, perforated particles with skeletal features. In a novel, alternative approach, LaTiO2N is prepared via the topotactic conversion of a double-layered Sillén-Aurivillius type oxyhalide material, La2·1Bi2·9Ti2O11Cl. The facile formation of LaTiO2N results in a perforated porous structure exhibiting skeletal features whilst maintaining a high surface area due to the presence of pores. By alternating the morphology of the material in this matter the oxygen evolution under one sun illumination is improved by around 10% or 30% depending on whether thermal ammonolysis of La2Ti2O7 is performed with or without flux, respectively.

Assessment of the impact of process and formulation variables on the prevalence of coating and coalescence mechanism in high shear mixer (Eirich mixer)

High shear mixing of powders in the presence of liquid addition can lead to the enlargement of primary powder particles, forming larger structures referred to as granules. This particle growth can occur through distinct mechanisms, including layering, coalescence, or a combination of both, and the prevailing mechanism is influenced by a multitude of process and formulation variables. In this study, we quantified the influence of process variables such as vessel inclination, rotational direction of the vessel, impeller speed, mixing duration, and rotation speed of the vessel pan on the particle growth mechanism. We accomplished this through rigorous image analysis of granule samples produced under varying conditions. Furthermore, our investigation extended to encompass the effects of formulation variables, including the particle density of the primary powder, the quantity of binder added, and the particle size of the coating material. Our findings revealed that the coating mechanism predominantly governed particle growth when the mixing time was brief, the mixer vessel had a high inclination angle, and the vessel rotated in a direction opposite to that of the agitator. The coating material utilization factor, denoting the ratio of the mass fraction of coating material added that effectively participates in the formation of coated seeds (each with a single seed) to the fraction of coating material engaged in competing mechanisms, serves as a crucial indicator of the prevailing mechanism within specific process and formulation conditions.

(Invited) Nucleation, Growth and Location Regulation of Heterogeneous Catalysts Synthesized by Atomic Layer Deposition

For supported catalysts, the particle surface or metal-support interface and its vicinity are the main areas providing active sites. In this regard, surface and interface engineering of heterogeneous catalysts is effective and critical for optimizing their catalytic performances. During the formation of active components, the structural uniformity, stability and location of nucleation sites determine the structural and scale uniformity, stability and environmental consistency of active sites, and ultimately determine their catalytic performance. Therefore, the regulation of nucleation, growth and location of active components is the key to precisely regulate the surface and interface structure and properties of supported catalysts. However, traditional preparation methods (such as impregnation method and precipitation method) have limitations in precise regulation of particle size, location and microstructure of catalysts due to the surface heterogeneity of supports and the high surface energy of nanoparticles, which makes it difficult to reliably reveal the structure-activity relationship of the catalyst. Therefore, the development of advanced fabrication methods is of vital significance to realize the nucleation, growth and location regulation of heterogeneous catalysts at atomic level precision. Atomic layer deposition (ALD) is a powerful scientific tool for catalytic research due to its self-limiting, atom-by-atom growth features. However, there is still a lack of rational knowledge of the nucleation and growth mechanism of catalytic particles prepared by ALD, the microscopic mechanism of interface structure modification, and the catalytic reaction mechanism. This is the topic of this lecture, in which we discuss the latest progress made in our group in precisely regulating the microstructure, size and location of ALD-deposited active components by several effective methods including nucleation site engineering, deposition kinetics engineering and template-assisted ALD method, as well as elucidating the nucleation and growth mechanism of ALD-deposited active components by in-situ and operando XAFS characterization based on our designed and built ALD-XAFS device. Through the above works, the nucleation and growth mechanisms of the deposited species and modification species, the microscopic mechanism of interface structure modification, and the influence of the size effect, the interface effect, and the distance effect on the catalytic performance were clarified. The structure-activity relationship was understood at the atomic/molecular level. These works will provide new ideas and scientific basis for the catalyst design and the performance regulation.

New Insights on the Formation of Nucleation Mode Particles in a Coastal City Based on a Machine Learning Approach.

Atmospheric particles have profound implications for the global climate and human health. Among them, ultrafine particles dominate in terms of the number concentration and exhibit enhanced toxic effects as a result of their large total surface area. Therefore, understanding the driving factors behind ultrafine particle behavior is crucial. Machine learning (ML) provides a promising approach for handling complex relationships. In this study, three ML models were constructed on the basis of field observations to simulate the particle number concentration of nucleation mode (PNCN). All three models exhibited robust PNCN reproduction (R2 > 0.80), with the random forest (RF) model excelling on the test data (R2 = 0.89). Multiple methods of feature importance analysis revealed that ultraviolet (UV), H2SO4, low-volatility oxygenated organic molecules (LOOMs), temperature, and O3 were the primary factors influencing PNCN. Bivariate partial dependency plots (PDPs) indicated that during nighttime and overcast conditions, the presence of H2SO4 and LOOMs may play a crucial role in influencing PNCN. Additionally, integrating additional detailed information related to emissions or meteorology would further enhance the model performance. This pilot study shows that ML can be a novel approach for simulating atmospheric pollutants and contributes to a better understanding of the formation and growth mechanisms of nucleation mode particles.

In Situ Liquid Cell Transmission Electron Microscopy Study of Studtite Particle Formation and Growth via Electron Beam Radiolysis.

This study presents in situ observations of studtite (UO2O2(H2O)2·2H2O) crystal growth utilizing liquid phase transmission electron microscopy (LP-TEM). Studtite was precipitated from a uranyl nitrate hexahydrate solution using hydrogen peroxide formed by the radiolysis of water in the TEM electron beam. The hydrogen peroxide (H2O2) concentration, directly controlled by the electron beam current, was varied to create local environments of low and high concentrations to compare the impact of the supersaturation ratio on the nucleation and growth mechanisms of studtite particles. The subsequent growth mechanisms were observed in real time by TEM and scanning TEM imaging. After the initial precipitation reaction, a post-mortem TEM analysis was performed on the samples to obtain high-resolution TEM images and selected area electron diffraction patterns to investigate crystallinity as well as energy-dispersive X-ray spectroscopy spectra to ensure that studtite was produced. The results reveal that studtite particles form through various mechanisms based on the concentration ratio of uranyl to H2O2 and that studtite is initially produced through an amorphous intermediary prior to formation of the crystalline material commonly reported in the literature.

The influence of water on size of the monodisperse polystyrene microspheres prepared by dispersion polymerization

AbstractPolystyrene microspheres with uniform sizes have a wide range of applications in biomedical engineering. However, detailed and systematic investigations on the influence of water content on alcohol/water systems are relatively scarce. In this study, the impact of trace water content on microsphere size was comprehensively examined, and a systematic exploration of the varying effects of different hydration levels on particle nucleation and growth mechanisms was conducted. When the water content increased from 0.1% to 0.4%, the microsphere diameter rapidly decreases from 3.6 to 2.71 μm. Correspondingly, the molecular weight increased from 29,797 to 69,186. However, within the water content range of 0.5%–14.5%, alterations in water content induced only slight variations in the microsphere diameter. The microsphere size, molecular weight, conversion rate, and reaction rate were compared in two stages. It was observed that the diminishing influence of water on the system was due to the changes in the main polymerization sites. Subsequently, the addition of water content up to 33.5% revealed an exponential decrease in the microsphere size with increasing water content in ethanol. This pattern was also observed in methanol and isopropanol, demonstrating its universality and predictability, making it applicable for precise prediction of microsphere size in different solvents.

Particle coating growth behaviors in a spray fluidized bed based on Gas-Liquid-Solid Quasi-Three-phase DEM numerical simulation

Wet granulation processes are widely used in chemical, food, pharmaceutical, and various other industrial processes. During the process of particle coating growth, particle fluidization state and liquid characteristics have an impact on the layer's thickness and homogeneity. In this study, discrete element, liquid bridge, and droplet motion models were combined to investigate the impact of injection gas velocity, droplet diameter and injection liquid viscosity on the particle growth ratio and coating thickness distribution, and the particle growth mechanism was investigated. The particle growth area, which is the area where the number of coated particles exceeds 0, was significantly expanded by decreasing the droplet diameter and increasing the gas velocity at appropriate ranges. The frequency of droplet and particle collisions increased, and average relative liquid content decreased with increasing particle growth area. By accelerating the injection of gas and reducing the viscosity of the injected liquid, the fluidization condition of the particles, which primarily affected the particle cycle frequency, could be enhanced. The improvement of particle growth area and particle cycle frequency allowed more particles to participate in growth and improved the quality of the grown particles. The proportion of small particles dramatically grew while the proportion of large particles reduced. The standard deviation of particle diameter decreased, and particle growth became more uniform.

Designing multifunctional silica coatings for enhanced broadband antireflection and microfiber contamination sensing

Multifunctional silica coatings find diverse applications in solar energy conversion and pollution monitoring sensors due to their suitability for mass manufacturing. However, the challenge lies in producing robust silica coatings on a large scale with tunable refractive index. This work presents a two-step acid/base catalyzed sol–gel process for synthesizing multifunctional silica coatings with adjustable refractive index. The coatings' porous microstructure allows them to be used as double-layer broadband antireflective coatings and enhances the sensitivity of contamination sensors. The optimized double-layer coatings, designed using computer-aided techniques, demonstrate excellent broadband antireflective performance in the visible regions and high environmental durability. They achieve a maximum transmittance of 99.87% at 591 nm, with an average transmittance of 99.40% in the visible region (400–800 nm) and 98.63% from 400 nm to 1100 nm. Additionally, the coatings exhibit robust abrasion resistance and enhanced surface hydrophobicity with a water contact angle increased from 30° to 126° through HMDS treatment. This work investigated the particle growth mechanism and the relationship between silica nanoparticle microstructure and antireflective coating properties. Furthermore, the coatings' presence of abundant micropores allows successful application onto microfiber contamination sensors, the additional loss increases from 26.40 dB to 37.69 dB over 140 min and decreases to 31.55 dB within one minute, demonstrating rapid adsorption and desorption rates. The work successfully achieves a wide range of adjustable refractive index while maintaining excellent mechanical and optical properties, addressing the traditional trade-off between high porosity and poor mechanical stability. These rationally designed multifunctional silica coatings hold great potential for high-quality broadband antireflection and high sensitivity in microfiber contamination sensing.

Advances of high-performance LiNi1-x-yCoxMyO2 cathode materials and their precursor particles via co-precipitation process

Layered LiNi1-x-yCoxMyO2 (M = Mn or Al) is a promising cathode material for lithium-ion batteries due to its high specific capacity and acceptable manufacturing cost. However, the polycrystalline LiNi1-x-yCoxMyO2 cathode material suffers from disordered orientation of primary particles and poor geometric symmetry of secondary particles, which severely hampers the migration of Li+ ions. Furthermore, the resulting anisotropy accelerates the disintegration of the secondary particle structure, significantly affecting the electrochemical performance of the polycrystalline cathode. In spite of less grain boundary, the single-crystal LiNi1-x-yCoxMyO2 cathodes still suffer from severe microcracks generated by repeated planar gliding during cycling, which poses a great challenge to the cycling stability of single-crystal materials. It's worth noting that the microstructure of the cathode material is mainly inherited from its precursor. Therefore, it is necessary to deeply understand the influence of the microstructure of Ni1-x-yCoxMy(OH)2 on the electrochemical properties of LiNi1-x-yCoxMyO2 cathode materials, so as to optimize the production process of preparing high-performance cathode precursors. In this review, we summarize recent advances in the research and development of Ni-rich cathode precursor materials. Firstly, the challenges faced by the Ni-rich hydroxide precursor materials are presented, including the effect of primary particle morphology and arrangement on the electrochemical performance of cathode materials, the influence of secondary particle morphology on lithium insertion reactions in cathode, and the effect of particle size on the microcracking of single-crystal particles. Secondly, the presentation of the conventional co-precipitation reactor, the mechanism of precursor particle growth, and the influence of co-precipitation parameters are described in detail. Finally, the strategies are systematically discussed to solve the challenges of hydroxide precursors, such as the innovation and optimization on reactants, synthesis processes, and reaction equipment. To obtain satisfactory high-quality precursor materials, future work will require an in-depth understanding of the reaction mechanism, combined with simulation techniques such as flow field theory calculations to guide the synthesis of precursors. This review provides a comprehensive analysis of the current progresses on the producing technologies of high-performance cathode precursors and offers prospects for future industry developments.

Microstructural understanding on the fouling behavior of crud on PWR fuel cladding surface

In the present paper, an accelerate crud creation experiment was conducted by a laboratory simulation facility. A TEM sample was prepared at the interface between the crud layer and pressurized water reactor (PWR) fuel cladding tube to investigate the fouling behavior of crud on the surface of cladding tubes at a microstructural level. The results show that the crud layer consisted mainly of NiFe2O4, as Fe3+ and Ni2+ serving as the primary sources. Heterogeneous growth of Fe3O4 was observed by HRTEM, which formed dislocations NiFe2O4 grains. Based on the microstructural characterization results, the growth mechanism of crud particles on cladding tube surface during subcooled nucleate boiling was discussed with a focus on mass and heat transfer.

Uniform growth of colloidal particles via internal gelation process

Nanocrystalline materials with excellent properties are of great interest, but little is known about how to maintain grain size uniformity, which is essential for the reliability of nanomaterials. A fascinating question is whether it is possible to achieve a narrow size distribution of colloidal clusters in the gel. The nanocrystalline materials could be prepared by sintering the gel. Based on the above ideas, the growth mechanism of colloidal particles in the zirconium-based sol-gel transition is studied. The study showed that the primary zirconium hydroxide colloidal particles based on zirconium tetramers would aggregate into clusters of about 70 nm due to the Brownian motion. The clusters would form the Zr-O-Zr bonds and the three-dimensional gel network structure. The three-dimensional gel network could restrict the movement of free water molecules, making the zirconium sol instantly transform into the zirconium gel. The aging temperature would not affect the size of the colloidal clusters in the zirconium gel. Therefore, the uniform nanocrystalline zirconia could be prepared by sintering zirconium gel, which demonstrated the superiority of the internal gelation process for preparing nanocrystalline materials.

Rapid growth of Aitken-mode particles during Arctic summer by fog chemical processing and its implication.

In the Arctic, new particle formation (NPF) and subsequent growth processes are the keys to produce Aitken-mode particles, which under certain conditions can act as cloud condensation nuclei (CCNs). The activation of Aitken-mode particles increases the CCN budget of Arctic low-level clouds and, accordingly, affects Arctic climate forcing. However, the growth mechanism of Aitken-mode particles from NPF into CCN range in the summertime Arctic boundary layer remains a subject of current research. In this combined Arctic cruise field and modeling study, we investigated Aitken-mode particle growth to sizes above 80 nm. A mechanism is suggested that explains how Aitken-mode particles can become CCN without requiring high water vapor supersaturation. Model simulations suggest the formation of semivolatile compounds, such as methanesulfonic acid (MSA) in fog droplets. When the fog droplets evaporate, these compounds repartition from CCNs into the gas phase and into the condensed phase of nonactivated Aitken-mode particles. For MSA, a mass increase factor of 18 is modeled. The postfog redistribution mechanism of semivolatile acidic and basic compounds could explain the observed growth of >20 nm h-1 for 60-nm particles to sizes above 100 nm. Overall, this study implies that the increasing frequency of NPF and fog-related particle processing can affect Arctic cloud properties in the summertime boundary layer.

Modified monoclinic metastable β-MoO3 submicrospheres: controllable preparation, phase identification, and their formation mechanisms

In this work, a modified monoclinic metastable β-MoO3 (identified as N-doped β-MoO3-θ) submicrospheres (SMSs) were prepared by the method of sublimation with using industrial MoO3 as the raw material in the range of 1173–1373 K. Various technologies such as XRD, SEM, FE-SEM, TEM, Raman, and XPS spectra were adopted to characterize the as-prepared product. The result showed that the phase composition of the as-prepared product had no obvious relationship with the reaction temperature and cooling condition, while the pumping speed of the system exerted important roles on it. When the pumping speeds were low (4 and 15 cm/s), uniform N-doped β-MoO3-θ SMSs were prepared; increasing the pumping speeds to 20 cm/s or higher, both N-doped β-MoO3-θ SMSs and α-MoO3 nanoplates (NPs) were appeared. Optimum conditions for the controllable preparation of N-doped β-MoO3-θ SMSs were recognized as 1273 K, water cooling, and with a pumping speed of 4–15 cm/s. The growth mechanism of large MoO3 spherical-shaped particles were due to the collision and gases deposition effects. This work also discovered that the cracking phenomena were often occurred on the surface of large MoO3 particles obtained under the air cooling and high pumping speed conditions, and the possible cracking mechanisms were illustrated.

Aggregation and Growth Mechanism of Ovalbumin and Sodium Carboxymethylcellulose Colloidal Particles under Thermal Induction.

Ovalbumin (OVA)/sodium carboxymethylcellulose (CMC) colloidal particles were prepared with different compactness and morphologies by regulating the interaction between proteins and polysaccharides during heating. Electrostatic interactions between the amine groups of OVA (-NH3+) and carboxyl groups of CMC (-COO-) enhanced complex formation. The protein conformation change benefited the hydrophobic interaction between the particles. Proteins in colloidal particles were unfolded/folded under thermal induction to form aggregates having more β-sheet structures. When the OVA/CMC ratio was 1:2, the initially loosely connected OVA/CMC aggregation changed into a uniform sphere between 25 and 90 °C. The mass ratio of OVA to CMC within the final colloidal particle (90 °C) was about 1:1.4. The OVA/CMC particle stability was maintained with hydrogen bonding, hydrophobicity, and disulfide bond. When OVA levels were predominant, OVA and CMC developed an approximately hollow sphere. Moreover, the final colloidal particle composition showed the OVA-to-CMC ratio as 3:1 (w/w). OVA bound into colloidal particle pores to increase compactness. Moreover, OVA and CMC bound to the colloidal particle while the particle shrank, thereby increasing the compactness of colloidal particles. There was a significant decrease in ABTS•+ scavenging activity of curcumin compared with that of the particles with a ratio of 1:2. Thus, the rational adjustment of the structure of colloidal particles could effectively enhance their functional characteristics, providing a new way for the controlled release of the active ingredients.