Kinetics Of Particle Growth Research Articles

Kinetics and optical properties of the silver nanoparticles in aqueous L64 block copolymer solutions

Silver nanoparticles were prepared by the chemical reduction of silver nitrate, AgNO 3, with excess of sodium borohydride, NaBH 4, in dilute aqueous solutions containing triblock copolymers poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) (PEO) Pluronic L64. The synthesis was completed in ∼24 h and produced highly stable particle dispersion. The growth of nanoparticles was assessed by combining Mie theory, UV–vis spectroscopy and dynamic light scattering, and the average particle size was determined from transmission electron microscopy. The silver nanoparticles were sterically stabilised as a result of the block copolymer adsorption onto the nanoparticle surface. Besides the stabilizing character, the copolymer affected the kinetics of particle growth, the size and optical properties of as-synthesized Ag nanoparticles. It was revealed that the particle formation took place in two distinct stages. The first step was dominated by Ag ion reduction and growth driven by accretion, while in the second stage coagulated clusters of nanoparticles were obtained obtained. The as-synthesized particles were polydisperse, the individual ones had a size of ∼7.6 nm as given by transmission electron microscopy, and the hydrodynamic radius of clusters amounted to 60 nm. The silver nanoparticles exhibited broad and structured emission bands centered at 300 and 330 nm for excitation wavelengths in two different ranges, 220–240 nm and 260–290 nm, respectively. This process may be assigned to two emission components corresponding to two different excitation wavelength domains.

Intercomparison of cloud condensation nuclei and hygroscopic fraction measurements: Coated soot particles investigated during the LACIS Experiment in November (LExNo)

Four cloud condensation nuclei (CCN) instruments were used to sample size‐selected particles prepared at the Leipzig Aerosol Cloud Interaction Simulator facility. Included were two Wyoming static diffusion CCN instruments, the continuous flow instrument built by Droplet Measurement Technologies, and the continuous flow Leipzig instrument. The aerosols were composed of ammonium sulfate, levoglucosan, levoglucosan and soot, and ammonium hydrogen sulfate and soot. Comparisons are made among critical supersaturation values from the CCN instruments and derived from measurements made with a humidified tandem differential mobility system. The comparison is quite encouraging: with few exceptions the reported critical supersaturations agree within known experimental uncertainty limits. Also reported are CCN‐ and hygroscopicity‐based estimates of the soot particles' solute fraction. Relative differences between these are as large as 40%, but an error analysis demonstrates that agreement within experimental uncertainty is achieved. We also analyze data from the Droplet Measurement Technologies and the two Wyoming static diffusion instruments for evidence of size distribution broadening and investigate levoglucosan particle growth kinetics in the Wyoming CCN instrument.

Similar Topological Origin of Chiral Centers in Organic and Nanoscale Inorganic Structures: Effect of Stabilizer Chirality on Optical Isomerism and Growth of CdTe Nanocrystals

It is observed in this study that the chirality of cysteine stabilizers has a distinct effect on both the growth kinetics and the optical properties of CdTe nanocrystals synthesized in aqueous solution. The effect was studied by circular dichroism spectroscopy, temporal UV-vis spectroscopy, photoluminescence spectroscopy, and several other microscopy and spectroscopic techniques including atomic modeling. Detailed analysis of the entirety of experimental and theoretical data led to the hypothesis that the atomic origin of chiral sites in nanocrystals is topologically similar to that in organic compounds. Since atoms in CdTe nanocrystals are arranged as tetrahedrons, chirality can occur when all four atomic positions have chemical differences. This can happen in apexes of nanocrystals, which are the most susceptible to chemical modification and substitution. Quantum mechanical calculations reveal that the thermodynamically preferred configuration of CdTe nanocrystals is S type when the stabilizer is D-cysteine and R type when L-cysteine is used as a stabilizer, which correlates well with the experimental kinetics of particle growth. These findings help clarify the nature of chirality in inorganic nanomaterials, the methods of selective production of optical isomers of nanocrystals, the influence of chiral biomolecules on the nanoscale crystallization, and practical perspectives of chiral nanomaterials for optics and medicine.

Biopolymer Nanoparticles from Heat‐Treated Electrostatic Protein–Polysaccharide Complexes: Factors Affecting Particle Characteristics

Biopolymer nanoparticles can be formed by heating globular protein-ionic polysaccharide electrostatic complexes above the thermal denaturation temperature of the protein. This study examined how the size and concentration of biopolymer particles formed by heating beta-lactoglobulin-pectin complexes could be manipulated by controlling preparation conditions: pH, ionic strength, protein concentration, holding time, and holding temperature. Biopolymer particle size and concentration increased with increasing holding time (0 to 30 min), decreasing holding temperature (90 to 70 degrees C), increasing protein concentration (0 to 2 wt/wt%), increasing pH (4.5 to 5), and increasing salt concentration (0 to 50 mol/kg). The influence of these factors on biopolymer particle size was attributed to their impact on protein-polysaccharide interactions, and on the kinetics of nucleation and particle growth. The knowledge gained from this study will facilitate the rational design of biopolymer particles with specific physicochemical and functional attributes.

Modeling Growth, Surface Kinetics, and Morphology Evolution in PETN

AbstractPentaerythritol tetranitrate (PETN) is a commonly used energetic material with both military and civilian applications. Good ignition properties mandate a powdered material with a high surface area. However, existing experimental data on PETN powder suggest an active surface that leads to particle coarsening and gradual reduction of the specific surface area over time. In this work we review some of the atomic‐level and coarse‐grained potential models developed for PETN and discuss their applications for studying particle morphology, growth, and surface kinetics, including molecular diffusion and evaporation/condensation rates. Simulation methods include classical molecular dynamics, kinetic Monte Carlo, and transition state calculations.

Short aspect ratio gold nanorods prepared using gamma radiation in the presence of cetyltrimethyl ammonium bromide (CTAB) as a directing agent

The synthesis of short aspect ratio gold nanorods using gamma radiation method by incorporating cetyltrimethyl ammonium bromide (CTAB) as a directing agent is reported in this communication. The radiolysis of Au +, in the presence of 2.5 nm Au seeds and 0.1 mol dm −3 isopropanol, results in the formation of Au spheres as evident from surface plasmon resonance band at 527 nm. However, by carrying out radiolysis at lower radiation dose rate, short aspect gold nanorods having surface plasmon bands at 513 and 670 nm have been prepared. The formation of rods at low radiation dose rate was observed to be governed by the kinetics of particle growth. The TEM of as-synthesized nanoparticles confirmed the formation of uniform sized nanorods having an aspect of 2.4.

Variant shape growth of nanoparticles of metallic Fe–Pt, Fe–Pd and Fe–Pt–Pd alloys

We report the controlled syntheses of Fe–Pt, Fe–Pd and Fe–Pt–Pd nanoparticles having different isolated shapes including sphere, cube, octopod-cube, star, rod, bilobe, tetrahedron, or multipod with size of 5–50 nm. The formation of such a rich variety of shapes was made possible by controlling the synthetic conditions (e.g. nature and concentration of the precursors, reaction time, temperature and atmosphere) of a thermal decomposition and reduction of precursors in the presence of surfactants. From the results of the investigation, the possible connection between formation of different shapes and the symmetry of the nuclei as well as the divergent kinetics of particle growth have been examined and discussed.

Ripening of nanowire-supported gold nanoparticles

Gold nanoparticles have applications ranging from catalysts for low temperature oxidation of CO to solar energy capture in the infrared. For all these applications, particle size and shape are critical. In this study, nanoparticle gold formed on GaN nanowires by plasma-enhanced chemical vapor deposition was annealed at temperatures ranging from 150 to 270 °C for 24 h. Particle size was measured before and after annealing using a field emission scanning electron microscope. Ripening of the gold particles was observed even at the lowest annealing temperatures of the study. The particle growth kinetics showed an Arrhenius relationship with activation energy of 27.38 kJ/mol. This value suggests that ripening occurs by particle migration and coalescence rather than adatom diffusion.

Chemical condensation model for the flow of a reacting mixture in a tube

A mathematical model for a continuous chemical vapor deposition (CVD) reactor is proposed. The simplest kinetics of chemical reactions and phase transitions in the bulk gas mixture and at the surface of the finely dispersed solid phase is used to study the interaction between micro-and macroscale phenomena. A quasi-steady microscale problem is solved analytically. A self-consistent numerical solution of the micro-and macroscale problems is used to obtain the fields of concentrations, temperature, distributions of fractions of the finely dispersed solid phase, and other parameters for different values of dimensionless numbers. The proposed model can be used to evaluate the phase structure, particle growth or evaporation kinetics, and the deposition rate of the solid phase.

Synthesis and Shape-Tailoring of Copper Sulfide/Indium Sulfide-Based Nanocrystals

Heterostructured Cu2S-In2S3 nanocrystals with various shapes and compositions were synthesized by a high-temperature precursor-injection method using the semiconductor nanocrystal Cu1.94S as a catalyst. The intrinsic cationic deficiencies formed at high temperature by Cu ions made the Cu1.94S nanocrystal a good candidate for catalyzing the nucleation and subsequent growth of In 2S3 nanocrystals, eventually leading to the formation of heterostructured Cu2S-In2S3 nanocrystals. Gelification of the reaction systems, which were composed of different types of nanocrystal precursors and solvent, was found to be a very effective measure for controlling the growth kinetics of the heterostructured particles. Consequently, matchsticklike Cu2S3-In2S3 heterostructured nanorods, teardroplike quasi-core/shell Cu2S@In2S3 nanocrystals, and pencil-like In2S3 nanorods were successfully obtained by manipulating the gelification of the reaction system; this formed a solid experimental basis for further discussion of the growth mechanisms for differently shaped and structured nanocrystals. By reaction with 1,10-phenanthroline, a reagent that strongly and selectively binds to Cu(+), a compositional transformation from binary matchsticklike Cu2S-In2S3 nanorods to pure In2S3 nanorods was successfully achieved.

D-17 Kinetics of Particle Growth for Supported Pt and Pt/Pd Determined Using HTXRD

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Characteristics of Magnetic Mesoparticles Fabricated by Electroless Nickel Deposition

A low-cost wet chemical process, viz., the electroless nickel deposition, was successfully developed to produce magnetic nickel−tungsten−phosphorus (NiWP) mesoparticles with diameters ranging from 100 to 500 nm on silica templates of ca. 102 nm and gold templates of ca. 3 nm. An X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX), a superconducting quantum interference device (SQUID), and a vibrating sample magnetometer (VSM) were employed to characterize these particles. The averaged sizes of the NiWP particles could be conveniently regulated with the duration of the electroless plating process, in which exponential growth kinetics of the NiWP particles was observed. Both XRD and electrodiffraction (ED) patterns of these NiWP alloys indicate existence of diffraction peaks close to the (111), (200), (220), and (311) reflections of bulk face-centered cubic (fcc) Ni. The zero-field-cooled (ZFC) and...

Phase-pure TiO2 nanoparticles: anatase, brookite and rutile

We report on the synthesis of phase-pureTiO2 nanoparticles in anatase, rutile and brookite structures, using amorphous titania as acommon starting material. Phase formation was achieved by hydrothermal treatment atelevated temperatures with the appropriate reactants. Anatase nanoparticles wereobtained using acetic acid, while phase-pure rutile and brookite nanoparticles wereobtained with hydrochloric acid at a different concentration. The nanomaterials werecharacterized using x-ray diffraction, UV–visible reflectance spectroscopy, dynamic lightscattering, and transmission electron microscopy. We propose that anatase formation isdominated by surface energy effects, and that rutile and brookite formation follows adissolution–precipitation mechanism, where chains of sixfold-coordinated titaniumcomplexes arrange into different crystal structures depending on the reactant chemistry.The particle growth kinetics under hydrothermal conditions are determined by coarseningand aggregation–recrystallization processes, allowing control over the average nanoparticlesize.

Antisolvent Precipitation of PDI 747: Kinetics of Particle Formation and Growth

The application of two recently developed protocols for the fast and robust determination of nucleation and growth kinetics to the antisolvent precipitation of PDI 747 is presented in this work. Both characterization methods are based on two in situ process analytical technologies, i.e., attentuated total reflection-Fourier transform infrared spectroscopy and focused beam reflectance measurement, to monitor the liquid and the solid phase during the characterization experiments. The method to determine growth rate kinetics is based on seeded batch desupersaturation experiments. It combines the accurate characterization of seed particle size distributions and the measurement of desupersaturation profiles for different experimental conditions with population balance modeling and an optimization routine to determine the growth mechanism and the kinetic parameters. In a second step, the growth kinetics are combined with induction time experiments to calculate the nucleation rate. Earlier, these protocols were ...

(Mini)emulsion Polymerization Kinetics Using Oil-Soluble Initiators

The mechanisms involved in the initiation of (mini)emulsion polymerization using oil-soluble initiators were investigated by means of a first principles model. The model was assessed by comparing its predictions with experimental data. The model shows that desorption of initiator radicals from droplets and particles is the key mechanism controlling the kinetics of miniemulsion polymerization and particle growth in emulsion polymerization. For these systems, the contribution of the fraction of the initiator dissolved in the aqueous phase is minor. In ab initio emulsion polymerization, the fraction of the initiator dissolved in the aqueous phase was the main contributor to micellar nucleation.

Preparation and optical properties of blue-emitting colloidal CdS nanocrystallines by the solvothermal process using poly (ethylene oxide) as the stabilizer

Blue-emitting colloidal CdS nanocrystals have been synthesized through the solvothermal reaction of cadmium acetate and thiourea in N,N-dimethylformamide using poly(ethylene oxide; PEO) as the stabilizing polymer. The as-prepared CdS colloids were stable at ambient conditions for several weeks. The PEO-stabilized CdS colloids showed a narrow fluorescence band with the maximum at about 420 nm and thus emitting blue fluorescence under the ultraviolet (UV) lamp. A common red shift of fluorescence band is not detected for the prepared CdS colloids in the study, indicating that PEO-stabilized CdS NCs possess few crystalline defects on their surface. In addition, transmission electron microscope micrographs reveal that the sizes of CdS NCs are between 4.4 to 5.4 nm with small standard deviations from 0.5 to 0.7 nm. The particle growth kinetics was studied by monitoring UV-visible absorption onsets versus the reaction time and was found to nearly follow the Lifshitz–Slyozov–Wagner theory for the Ostwald ripening mechanism.

Modeling of particle growth: Application to water treatment in a fluidized bed reactor

Abstract Crystallization process in a fluidized bed reactor to remove fluoride from industrial wastewaters has been studied as a suitable alternative to the chemical precipitation, which generates large amounts of a water rich sludge that must be disposed of with increasing costs. The major advantage of this technology is the decrease of sludge formation, the simplification of the materials recovery procedures and the reduction of solid wastes. Removal of fluoride by crystallization process has been carried out in a laboratory-scale fluidized bed reactor focused to the analysis of the influence of the supersaturation (S), the up-flow velocity (SV) and the amount and mean diameter of seed material (L0) on the process efficiency, which are related to the crystal growth. In the modeling, design and control of a fluidized bed reactor for water treatment it is necessary to study the particle growth kinetics. From the results obtained in this study, it has been proposed a growth model represented by the equation G = 2.96 × 10 − 5 L 0 1.37 S V 0.5 S ( m s − 1 ) , which fits well the experimental data in the interval of variables studied.

Particle growth kinetics of calcium fluoride in a fluidized bed reactor

Crystallization process in a fluidized bed reactor to remove fluoride from industrial wastewaters has been studied as a suitable alternative to the chemical precipitation in order to decrease the sludge formation as well as to recover fluoride as synthetic calcium fluoride. In the modeling, design and control of a fluidized bed reactor for water treatment it is necessary to study the particle growth kinetics. Removal of fluoride by crystallization process in a fluidized bed reactor using granular calcite as seed material has been carried out in a laboratory-scale fluidized bed reactor in order to study the particle growth kinetics for modeling, design, control and operation purposes. The main variables have been studied, including superficial velocity ( SV, m s - 1 ), particle size of the seed material ( L 0 , m) and supersaturation ( S ). It has been developed a growth model based on the aggregation and molecular growth mechanisms. The kinetic model and parameters given by the equation G = ( 2.26 × 10 - 10 + 2.82 × 10 - 3 L 0 2 ) SV 0.5 S fits well the experimental data for the studied range of variables.

On the influence of the treatment of aerosol particles in different bin microphysical models: A comparison between two different schemes

In this paper, we compare two bin microphysical models, 1) EXMIX (EXternally MIXed) with two-dimensional distribution functions that cover the aerosol particle sizes as well as the hydrometeor sizes (120 bins from 8 nm to 7 mm) and 2) DESCAM (DEtailed SCAvenging Model) that uses separate one-dimensional functions for aerosol particles and drops. EXMIX, thus, treats the activation process in a continuous way whereas DESCAM has to manage the transfers between the aerosol particle and the droplet reservoirs thanks to threshold values such as the critical radius of activation. The analysis and comparison of the models' results show that firstly, it is necessary to introduce a temperature dependency in the activation process to stay consistent with the kinetics of aerosol particle growth and secondly, with the temperature correction proposed, DESCAM results are in good agreement with EXMIX results although the treatment of the aerosol particles is quite different in the two models. Furthermore, it is shown that DESCAM is able to reproduce quite well the main features of continental as well as maritime-type clouds, even with a low bin resolution for the microphysical grids. Finally, as DESCAM needs much less computer resources than EXMIX, it seems to be a good candidate for future use in a three dimensional framework.

Hygroscopic growth and water uptake kinetics of two-phase aerosol particles consisting of ammonium sulfate, adipic and humic acid mixtures

The hygroscopic growth of solid aerosol particles consisting of mixtures of ammonium sulfate and either adipic acid or Aldrich humic acid sodium salt was characterized with a hygroscopicity tandem differential mobility analyzer and an electrodynamic balance. In particular, the time required for the aerosol particle phase and the surrounding water vapor to reach equilibrium at high relative humidity (RH) was investigated. Depending on the chemical composition of the particles, residence times of > 40 s were required to reach equilibrium at 85% RH, yielding up to a 7% reduction in the measured hygroscopic growth factors from measurements at 4 s residence time compared to measurements at equilibrium. We suggest that the solid organic compound, when present as the dominant component, encloses the water-soluble inorganic salt in veins and cavities, resulting in the observed slow water uptake. Comparison with predictions from the Zdanovskii–Stokes–Robinson relation shows enhanced water uptake of the mixed particles. This is explained with the presence of the salt solution in veins resulting in a negative curvature of the solution meniscus at the opening of the vein. In conclusion, it is important for studies of mixtures of water soluble compounds with insoluble material to allow for sufficient residence time at the specified humidity to reach equilibrium before the hygroscopicity measurements.