Particle Formation Process Research Articles

Simulations on time scales and conversion of fast competing reactions in rapid mixing

This work studies the fast coupling reaction of polymers with a water competition under confined impinging jet (CIJ) mixing. The coupling reaction between polystyrene acyl chloride (PS-COCl) and polyethylene glycol amine (PEG-NH2) is used either with or without a water competition. The reactions are implemented either in a molecular homogeneous and perfect mixing or in a CIJ mixing reactor. The simulations reveal that although the process with Rej = 1770 is mixing limited (τrxn1 (∼1.8 ms) < τrxn2 (∼7.4 ms) < τmix (∼8.5 ms)), the desired coupling conversion (16%) and selectivity (0.17) is approaching to 18% and 0.19 respectively, which were their maxima occurred in a molecular homogeneous and perfect mixing. The simulation results successfully rationalize the low coupling conversion of about 17% reported in a previous experiment. Moreover, this study provides guidance to improve the desired conversion by increasing either [PEG-NH2]0/[PS-COCl]0 or k2/k1, which is crucial for the in-situ reactive flash nanoprecipitation (RFNP) to generate stable nanoparticles, especially with a higher drug load and less reactive polymers. The successful acquisition of the time scales of the competing reactions and mixing would be beneficial to revealing the mechanism and process of particle formation and evolution in the RFNP, where time scales of chemical reactions, mixing, and precipitation would compete to each other.

Synthesis of nanometric silica particles via a modified Stöber synthesis route

In this paper we describe a simple modification of the classic Stöber reaction enabling a high temperature synthesis of nanometric silica particles with diameters less than 100nm in sealed reaction tubes. This could be reached due to the replacement of the basic catalyst ammonia by ethanolamine. Thus, high temperature synthesis up to 80°C can be run without facing the risk of bubble formation inside the reaction tube. The modified synthesis route enables the synthesis of spherical silica nanoparticles with mean diameters between 28 and 647nm and standard deviations less than 10% as well as smooth surface structures. This work deals with basic studies on the use of ethanolamine for the synthesis of silica nanoparticles in alkaline media in sealed reaction tubes under ambient pressure. These include experiments on the adjustment of the particle size depending on the composition of the reaction solution and the temperature. In addition, reaction kinetics of the particle formation process are monitored as a function of temperature and the influence of the mixing time on the particle size is investigated.

Particle size distribution, chemical composition and meteorological factor analysis: A case study during wintertime snow cover in Zhengzhou, China

There was a significant snowfall event in North China from November 23 to 25 in 2015. Considering that most of the bare surface and road dust were covered by snow, the effect of dust and soil could be ignored. Atmospheric particle samples were collected in Zhengzhou, China during a haze event from November 28 to December 4, 2015. To better understand the formation and evolution of this hazy event, the size distribution, particle number, composition of particles and meteorological parameters were measured and analyzed. Results show that the meteorological conditions played an important role in the occurrence and elimination of this event. The hourly fine particle matter (PM2.5) concentration was positively correlated with relative humidity (r=0.84, p<0.01) but negatively correlated with wind speed (r=−0.62, p<0.01). The particle mass concentrations peaked at the sizes of 1.0 to 1.6μm on hazy days, however, the total particle number concentrations on hazy days were lower than those on clean days. The median diameter of the number concentration during hazy days was approximately 60nm, whereas it was 26nm on clean days. Two new particle formation processes were observed on the clean days both. The proportion of secondary inorganic ions (SO42−, NO3− and NH4+) on hazy days was higher than that on clean days. The higher NH4+ concentration in this case may be contributed by traffic and coal-power emission. Crustal matter accounted for 2.4% in PM2.5 on hazy days, and it confirmed that the contribution of dust emission source was negligible during this event. The ratios of NO3−/SO42− ranging from 0.41 to 0.67 indicated the relative importance of stationary combustion. The ratios of OC/EC varied from 2.73 to 3.42 and indicated the presence of secondary organic carbon. Effective haze mitigation should enforce pollutant control measures for primary emission (dust) and secondary aerosol gaseous precursor (NH3, NO2 and SO2).

Theoretical Investigation of the Influence of Different Chamber Geometries on the Agglomeration Capacity of Carbon Dioxide

This paper addresses the complicated process of carbon dioxide particle formation (agglomeration), which is essential for carbon dioxide snow blasting. Most effective process methods in this field possess a dedicated location where agglomeration is likely to occur. Research has shown that successful agglomeration is a key factor when cleaning or deburring with solid carbon dioxide. The following describes the mechanisms of carbon dioxide (CO2) snow agglomeration inside this so-called agglomeration chamber. The elements of larger size, as well as an irregular shape directly lead to the increase of effectiveness. Therefore, it is necessary to determine how to improve this process for the purpose of dealing with difficult workpieces and materials and broaden the possibilities of carbon dioxide blasting. One of the main factors of agglomeration is turbulence. In short, the more turbulent activity that takes place, the better is the particle formation of solid carbon dioxide. Numerous geometries were created with different inserts, such as static mixers or angled tubes, in hope to increase turbulence. The basic idea is to implement these geometries in computational fluid dynamics (CFD) and finally proceed to an evaluation and comparison of the simulation results, in order to select the best candidates for optimization and realization.

Mechanism of Particle Formation in Silver/Epoxy Nanocomposites Obtained through a Visible-Light-Assisted in Situ Synthesis.

A detailed understanding of the processes taking place during the in situ synthesis of metal/polymer nanocomposites is crucial to manipulate the shape and size of nanoparticles (NPs) with a high level of control. In this paper, we report an in-depth time-resolved analysis of the particle formation process in silver/epoxy nanocomposites obtained through a visible-light-assisted in situ synthesis. The selected epoxy monomer was based on diglycidyl ether of bisphenol A, which undergoes relatively slow cationic ring-opening polymerization. This feature allowed us to access a full description of the formation process of silver NPs before this was arrested by the curing of the epoxy matrix. In situ time-resolved small-angle X-ray scattering investigation was carried out to follow the evolution of the number and size of the silver NPs as a function of irradiation time, whereas rheological experiments combined with near-infrared and ultraviolet-visible spectroscopies were performed to interpret how changes in the rheological properties of the matrix affect the nucleation and growth of particles. The analysis of the obtained results allowed us to propose consistent mechanisms for the formation of metal/polymer nanocomposites obtained by light-assisted one-pot synthesis. Finally, the effect of a thermal postcuring treatment of the epoxy matrix on the particle size in the nanocomposite was investigated.

The soot particle formation process inside the piston bowl of a small-bore diesel engine

The present study unveils the soot formation processes occurring inside the piston-bowl of a small-bore diesel engine by conducting the thermophoresis-based soot sampling experiments at various locations along the flame development path. Based on planar laser-induced incandescenece (PLII) and planar laser-induced florescence of hydroxyl (OH-PLIF) imaging performed in the same optical engine previously, it was understood that the sooting flame impinges on and then flows along the bowl wall, suggesting a soot growth and persistence near the fuel-rich wall region. In the present study, a soot sampling probe is placed in five different locations including the flame–wall impingement point and four further downstream regions: two 60° and two 120° from the jet axis with two different distances from the bowl wall in each angle. Methyl decanoate is selected as a surrogate fuel due to its low-sooting propensity and thus reduced laser attenuation in the reference PLII images; however, the fuel produces high enough number of soot particles for the in-flame sampling and their statistical analysis. The transmission electron microscope (TEM) images of the sampled soot particle aggregates and their statistical analysis of sizes and fractal dimensions as well as nanoscale internal pattern of the soot primary particles show that precursor-like, small soot particles with amorphous internal carbon layer structures form in the flame–wall impingement region, which grow in size and become large soot aggregates as travelling along the bowl wall. The detailed analysis clearly indicates that the soot precursors underwent the surface growth, aggregation and coagulation to produce large, long-stretched soot aggregates during which the amorphous soot carbon layers transformed into a typical core–shell structure. At further downstream locations, the continued surface growth increases the size of soot primary particles in the core region of the soot aggregates while the oxidation of the soot primary particles located in the outer region tends to reduce the aggregate size, resulting in more compact structures. In the outer region of the flame, the intensive soot oxidation induced by the hydroxyl attack further reduces the size of large soot aggregates and at the same time, eliminates the small soot aggregates. Throughout these soot formation/oxidation processes, the soot carbon layer gaps continue to decrease, indicating more mature soot primary particles.

Diamines Can Initiate New Particle Formation in the Atmosphere.

Recent experimental evidence suggests that diamines can enhance atmospheric new particle formation more efficiently compared to monoamines such as dimethylamine. Here we investigate the molecular interactions between sulfuric acid (sa) and the diamine putrescine (put) using computational methods. The molecular structure of up to four sulfuric acid molecules and up to four putrescine molecules were obtained at the ωB97X-D/6-31++G(d,p) level of theory. We utilized a domain local pair natural orbital coupled cluster method (DLPNO-CCSD(T)/aug-cc-pVTZ) to obtain highly accurate binding energies of the clusters. We find that the (sa)1-4(put)1-4 clusters show more ionic character than clusters consisting of sulfuric acid and dimethylamine (dma) by readily forming several sulfate ions in the cluster. To estimate the stability of the clusters, we calculate the evaporation rates and compare them to ESI-APi-TOF measurements. Using the atmospheric cluster dynamics code (ACDC), we simulate and compare the new particle formation rates between the (sa)1-4(put)1-4 and (sa)1-4(dma)1-4 cluster systems. We find that putrescine significantly enhances the formation of new particles compared to dimethylamine. Our findings suggest that a large range of amines with different basicity is capable of explaining various regions of the observed new particle formation events. These results indicate that diamines, or related compounds with high basicity, might be important species in forming the initial cluster with sulfuric acid and subsequently more abundant amines with lower basicity can assist in the new particle formation process by attaching to the sulfuric acid-diamine nucleus.

Development of a global aerosol model using a two‐dimensional sectional method: 1. Model design

AbstractThis study develops an aerosol module, the Aerosol Two‐dimensional bin module for foRmation and Aging Simulation version 2 (ATRAS2), and implements the module into a global climate model, Community Atmosphere Model. The ATRAS2 module uses a two‐dimensional (2‐D) sectional representation with 12 size bins for particles from 1 nm to 10 μm in dry diameter and 8 black carbon (BC) mixing state bins. The module can explicitly calculate the enhancement of absorption and cloud condensation nuclei activity of BC‐containing particles by aging processes. The ATRAS2 module is an extension of a 2‐D sectional aerosol module ATRAS used in our previous studies within a framework of a regional three‐dimensional model. Compared with ATRAS, the computational cost of the aerosol module is reduced by more than a factor of 10 by simplifying the treatment of aerosol processes and 2‐D sectional representation, while maintaining good accuracy of aerosol parameters in the simulations. Aerosol processes are simplified for condensation of sulfate, ammonium, and nitrate, organic aerosol formation, coagulation, and new particle formation processes, and box model simulations show that these simplifications do not substantially change the predicted aerosol number and mass concentrations and their mixing states. The 2‐D sectional representation is simplified (the number of advected species is reduced) primarily by the treatment of chemical compositions using two interactive bin representations. The simplifications do not change the accuracy of global aerosol simulations. In part 2, comparisons with measurements and the results focused on aerosol processes such as BC aging processes are shown.

Understanding the process-product-performance interplay of spray dried drug-polymer systems through complete structural and chemical characterization of single spray dried particles

A complete description of the particle formation process can only be realized with techniques that enable the measurement of the composition and structural dependence of individual particles.The purpose of this publication is to highlight the utility of one such high resolution imaging technique; focused-ion scanning electron microscopy (FIB-SEM). As a model system, amorphous dispersion particles of felodipine and polyvinylpyrrolidone (PVP) were prepared by spray drying and used to interrogate single particles. Further, FIB-SEM was coupled with energy dispersive X-ray analysis (EDX) to characterize spatial chemical distributions in spray dried amorphous solid dispersion particles. Within a single spray drying batch, individual particles exhibited different phase behavior as a function of particle size. Larger particles showed notable amorphous-amorphous phase separation while smaller particles showed uniform composition. The morphology of particles was also found to be a function of particle size. Larger particles were consistently more porous in nature compared to smaller particles. The observed differences in compositional heterogeneity of different spray dried particles as a function of size are interpreted via theoretical arguments based on the Peclet number, the ratio of the evaporative flux of the solvent to the diffusive flux of the drug and the polymer within the droplet. Phase behavior may also be interpreted in terms of equilibrium ternary phase diagrams. Regardless, commonly used bulk physical and chemical characterization techniques may be used to establish correlations between the nature of the dispersion and the processing parameters. However, these techniques lack the resolution to provide a scientific link between the processing conditions and the nature of individual particles. The current paper highlights the utility of high resolution morphological and compositional measurements of individual particles.

In‐Situ Observation of Nanoparticle Formation Under Different Power of Microwave Irradiation

AbstractMicrowave technology has emerged as one of the useful methods for nanoparticle synthesis. Despite many studies on this area, its underlying mechanism has not been clearly understood. In this study, in‐situ observation of nanoparticle growth was carried out and the profiles and behaviors of produced bubbles and particles under microwave effect were reported. Sizes of bubble and nanoparticle particle were measured during and after microwave irradiation using a DLS apparatus and behavior of particle growth and superheating effect were observed. From the experimental data, it is apparent that the maximum bubble sizes were greatly influenced by the irradiation power and solute concentration. Particle number density, which is related to the initial solute concentration, is also an important factor for the bubble size produced during the irradiation. Finally, through in‐situ observation of superheating effect, the behavior was frequently caused by the irradiation at higher power. To prevent superheating effect, influencing factors such as the irradiation power and number density should be controlled to ensure a stable operation of particle formation process.

Sources and Characteristics of Regional Background PM1 in North China During the Autumn and Winter Polluted Period

The campaign of investigating the chemical compositions and particle size distributions of NR-PM1(non-refractory PM1) was conducted by using a High Resolution Time of Flight Aerosol Mass Spectrometer(HR-ToF-AMS) at the Shangdianzi(SDZ) regional atmospheric background site(117.07°E, 40.39°N), northeast of Beijing, from October 17th 2015 to January 27th 2016. The results showed that organics was the main component of PM1, and the proportion of nitrate was higher than that of sulfate in autumn and winter. The mean mass-resolved size distributions for the main components displayed accumulation mode. The wider organic peak shape and larger nitrate peak size indicated that the organics contributed to both small and large particles at the beginning of the particle formation, growth and aging processes, while most of nitrate particles preferred to grow into large particles during the aging process. The ratios of elements between OM and OC, O/C and H/C were calculated as 1.91, 0.58 and 1.58 respectively. The slope of Van Krevelen diagram of organic aerosols during polluted episode was -0.21, whose oxidation state was higher than those of other city sites. Nitrate was the major contributor of NR-PM1 during the polluted period, while organics was significantly higher than that during clean period. The results of back trajectories analysis demonstrated that the air masses were complex during the pollution episode. The northwest wind from central Inner Mongolia and Siberia dominated the clean episodes, which was conducive to the spread of pollutants.

Spray-drying-assisted reassembly of uniform and large micro-sized MIL-101 microparticles with controllable morphologies for benzene adsorption

Significant research has been focused on the synthesis of metal-organic frameworks (MOFs) with controllable compositions and structures, while much fewer works have been devoted to the construction of large micro-sized MOFs with uniform sizes and morphologies, which could be beneficial for practical applications. In this paper, a unique microfluidic jet spray drying technology has been adopted to reassemble nano-sized MIL-101 building blocks into hierarchical microparticles with uniform and large particle sizes. Specifically, suspension precursors of nano-sized MIL-101 building blocks are atomized into uniform droplets and then converted to microparticles on a one-to-one basis through a fast and scalable spray drying process. The particle size and morphology can be controlled by adjusting the solid concentration of the suspension and the drying temperature. The particle formation process with evolution of different morphologies are discussed. The resultant uniform MIL-101 microparticles possess hierarchical porosities and maintain the intrinsic crystal structure, microporosity and thermal stability of the nano-sized building blocks. They demonstrate a high efficiency toward benzene adsorption from n-octane solutions with high adsorption rates and very high adsorption capacities under batch conditions. Moreover, the large particle size and hierarchical structure make them applicable as filler of a fixed bed for dynamic flow separation of benzene from n-octane solutions with promising performance. The microfluidic jet spray drying technology can also be extended for the reassembly of other uniform MOF microparticles.

A novel multiscale model for the simulation of polymer flash nano-precipitation

Numerous models describe the flash nano-precipitation (FNP) process to form polymer nanoparticles, however most of them are based on equilibrium approaches and are not capable of predicting kinetically stable configurations. Moreover, since FNP occurs through solvent-displacement, the way in which the solvent and anti-solvent are mixed plays an important role, which is often overlooked. Here we propose a multiscale approach, which combines molecular dynamics (MD), a Smoluchowski population balance equation (PBE) and computational fluid dynamics (CFD), to model the FNP process, from the atomistic-scale up to the macro-scale. The particle formation process is not described with the usual nucleation-and-growth approach, but as Brownian aggregation of the polymer molecules into nanoparticles. Being the final nanoparticles amorphous, no energy barrier to the aggregation process is considered, whereas the effects of both turbulent mixing and turbulent aggregation on the evolution of the nanoparticles are accounted for. The main novelty of this work is that the aggregation kernel appearing in the PBE, coupled in turn with CFD, is calculated from MD simulations, following the multiscale modeling paradigm. The model is tested on the FNP of poly-ε-caprolactone nanoparticles in acetone-water mixtures. Predictions for the final mean nanoparticle size are found in good agreement with experiments, especially at high initial polymer concentrations, where the hypothesis of no energy barrier is more realistic.

Preparation and characterization of dispersions based on chitosan and poly(styrene sulfonate)

Interpolyelectrolyte complexes (IPECs) were obtained by the mixture of solutions of chitosan and poly(sodium 4-styrene-sulfonate). The resultant dispersions were characterized using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Gyration radius from SAXS increased as sulfonate to aminium molar ratio, r SA , increased, while pair distance distributions, P(r), shifted to higher values of r, describing the process of particle formation as resultant from collapse of solubilized IPEC clusters in the form of solid particles, followed by nucleation of larger ones. Intensity correlation curves from DLS were used to obtain parameters related to Brownian motion of (or within) IPEC clusters. IPEC cluster dimension growth was related to characteristic relaxation rate and relaxation rate distribution width. Association of DLS-derived results to SAXS-resultant data yielded a description of nanoparticles made of solid IPEC clusters stabilized by solubilized IPEC species.

Development of polyester resin particles for toner with a controlled particle size distribution and shape

We developed new polyester resin particles for use in toner that are prepared by an advanced dissolution suspension method. The new resin particles have excellent characteristics, such as a narrow particle size distribution, a uniform and non-spherical particle shape and high melt elasticity at high temperature with low-temperature meltability. The narrow particle size distribution, which has a coefficient of variation (CV) under 20%, is obtained by using nanoscale styrene-acrylic particles during the particle formation of the dissolution suspension process. The styrene-acrylic particles are prepared by emulsion polymerization and act as a particle size control agent in the formation of the polyester particles by adsorption on the surface of the polyester solution droplets through the hetero-coagulation effect. The particle shape is controlled from spherical to non-spherical forms, such as spindle or dimple shapes, during the solvent removal process. Moreover, a melting property suitable for toner application is achieved by the elongation reaction of the polyester prepolymer proceeding simultaneously during the particle formation process. This review introduces the outlines of the technical features and the key processes. Novel polyester resin particles useful for toner with characteristics such as a narrow particle size distribution, a uniform and non-spherical particle shape, and high melt elasticity at high temperature with low-temperature meltability were developed. These characteristics were achieved by the application of three key technologies to the conventional dissolution suspension method, and they contribute to energy savings and high image quality for toner.

Synthesis, Characterization and Antibacterial Activity of Ciprofl oxacin Loaded Polymer Nanoparticles for Parenteral Application

Different polymerization techniques as particle formation processes for ciprofl oxacin-loaded poly (butyl cyanoacrylate) nanoparticles (CfH-PBCN) were evaluated to choose the most appropriate in terms of the resulting nanoparticles characteristics suitable for parenteral administration.

Fluorescence Spectroscopy as a Tool to Unravel the Dynamics of Protein Nanoparticle Formation by Liquid Antisolvent Precipitation

Protein-based particles are very promising colloidal systems for protection and controlled release applications in the food, cosmetics and pharmaceutical sector. One technique to produce these protein colloidal particles is liquid antisolvent precipitation (LAS). Despite the simplicity and versatility of LAS, not much is known about the protein conformational changes and interactions that are at the basis of the particle formation process. In this study, steady state fluorescence experiments using intrinsic fluorophores were evaluated as a tool to unravel the dynamics of the protein nanoparticle formation. Colloidal whey protein isolate and gliadin particles were produced by LAS. Changes in particle diameter (distribution), polydispersity index and photophysical properties of intrinsic fluorophores were monitored as a function of antisolvent concentration. By combining dynamic light scattering with photophysical data, a model of the changes occurring during particle formation and disintegration could be proposed. The results suggest that particle formation and disintegration are fully reversible processes during which the main changes in protein conformation (around the fluorescent probes) occur at the same antisolvent concentrations. In principle, steady state fluorescence measurements using intrinsic probes can indeed be used to effectively report on (part of the) conformational changes for both protein systems under study.

Formation process of core‐shell microparticles by solute migration during drying of homogenous composite droplets

Particle formation process during spray drying profoundly impacts particle morphology and microstructure. This study experimentally investigated the formation of core‐shell‐structured microparticles by one‐step drying of composite droplets made of Eudragit® RS (a polycationic acrylic polymer in nanoparticle form) and silica sol. The formation of an incipient surface shell was monitored using single droplet drying technique, and the freshly formed shell was recovered for subsequent analyses. Adding silica to RS precursor increased the shell formation time and altered the properties of the incipient shell from water‐dispersible to nondispersible. The incipient shell formed from RS/silica droplets with mass ratios of 1.5%:1.5% and 0.5%:2.5% showed ingredient segregation with a preferential accumulation of RS, similar to the shell region of dried microparticles. After shell formation, excess silica sol in the liquid phase could flow inward, producing a dense core. This mobility‐governed solute migration would be useful for constructing core‐shell microparticles using other precursor systems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3297–3310, 2017

Synthesis of Magnetic Nanoparticles by Ultrashort Pulsed Laser Ablation of Iron in Different Liquids.

Magnetic nanoparticles were generated by ultrashort pulsed laser ablation of an iron target in water, methanol, ethanol, acetone and toluene. The relationship between ablation rate, liquid properties and the physical and chemical properties of the nanoparticles was studied. Composition, morphology and magnetic properties were investigated by TEM, XPS and vibrating-sample (VSM) and SQUID magnetometry. The properties of the generated nanoparticle ensembles reflected the influence of the liquid environment on the particle formation process. For example, the composition was strongly dependent on the carbon to oxygen ratio within the molecules of the liquid. In contrast to short pulsed laser ablation in liquids, the nanoparticles generated by ultrashort pulses had a higher level of polycrystallinity.

Precipitation of curcumin by pressure reduction of CO2-expanded acetone

In this work, a technique of precipitation by pressure reduction of gas-expanded liquids (PPRGEL) has been utilized to precipitate ultra-fine particles of curcumin. Curcumin is a natural and pharmaceutically viable compound found in Indian spice, turmeric and possesses several medicinal properties. However, it suffers from low bioavailability due to its poor solubility in aqueous medium. Precipitation of ultrafine particles of such compounds improves their bioavailability due to increase in surface area and hence the dissolution rates. The PPRGEL process precipitates ultra-fine particles by generating large, rapid and uniform supersaturation in the solution produced by a sudden and large reduction (40–70K) in the solution temperature in a very short time (as low as 1min). In this work it was found that the particle size, size distribution and polymorphic behaviour of precipitated curcumin particles depends on initial CO2 pressure as well as on the additives used. Curcumin particles mostly precipitated in monoclinic form. However, curcumin particles precipitated at 40bar and with additives such as Tween 80 and PF68 were found to precipitate as a mixture of orthorhombic and monoclinic forms. Dissolution studies show that the precipitated curcumin particles dissolve faster than raw curcumin. Further, a mathematical model was used to estimate supersaturation, nucleation rates, growth rates and average sizes of particles precipitated by PPRGEL. Comparison of experimental particle sizes with the predicted particle sizes suggests that at lower initial pressures, heterogeneous nucleation mechanism dominates the particle formation process and at higher initial pressures, homogeneous nucleation mechanism seems to dominate the particle formation process.