Final Particle Diameter Research Articles

Comparative Assessment of Comminution Energy Equations (Models) Using Some Selected Legumes, Tubers, Cereals and Sea Food

The quest to predict more precisely energy that is just enough to achieve closely any desired final particle size of food material subjected to comminution is necessary. This is to avoid energy wastage, obtain finer product size(s) that are uniform and can encourage easy mixing, dehydration/drying, etc. In this regard, some selected legumes (soybeans and beans), cereals (sorghum, millet, corn and wheat), sea food (crayfish) and tubers (cassava and yam) were subjected to comminution through the application of some major energy equations (models); as they find various applications in food industries. Four energy equations (models) namely the Kick’s, Rittinger’s and Bond’s for size reduction and the OruaAntia’s minimum energy equation for mass-size reduction were employed. The constant in each equation (model) to be applied in grinding of selected food materials was determined and used in obtaining the required specific energy of comminution needed to accomplish desired final product size(s). The corresponding grinding time expected to achieve the desired final product were computed and used in operating the grinding machine. Results revealed that the OruaAntia’s minimum energy equation for mass-size reduction operation may be applied on the selected food materials to achieve very closely any desired final average particle diameter with a percentage deviation of 1.66% followed with Rittinger’s equation having average percentage deviation of 6.88%. Technical analysis re-affirm that Kick’s equation could only achieve coarse particles as the final particle size showed average percentage deviation of 38.40%, while Bond’s equation may be limited to prediction of coarse and intermediate particles; since the final particle size average percentage deviation was 16.19%. Besides using Rittinger’s energy equation to obtain fine particles, the use of Orua Antia minimum energy equation may possibly further achieve desired finer particle size(s).

Time-Resolved Small-Angle X-ray Scattering Studies during the Aqueous Emulsion Polymerization of Methyl Methacrylate.

Recently, we reported time-resolved synchrotron small-angle X-ray scattering (TR-SAXS) studies during aqueous emulsion polymerization using a bespoke stirrable reaction cell (J. Am. Chem. Soc. 2021, 143, 1474-1484). This proof-of-concept study utilized a semifluorinated specialty monomer (2,2,2-trifluoroethyl methacrylate) to ensure high X-ray contrast relative to water. Herein, we extend this approach to emulsion polymerization of methyl methacrylate (MMA) in the presence or absence of sodium dodecyl sulfate (SDS) at 70 °C. Solution conductivity measurements for this anionic surfactant indicated a critical micelle concentration (CMC) of 10.9 mM at this temperature. Thus, SDS was employed at either 1.0 or 20.0 mM, which corresponds to well below or well above its CMC. Postmortem analysis by 1H NMR spectroscopy indicated MMA conversions of 93-95% for these three formulations. We demonstrate that the X-ray contrast between water and PMMA is sufficiently large to produce high-quality scattering patterns during TR-SAXS experiments. Such patterns were fitted using a hard-sphere scattering model to monitor the evolution in particle diameter. This enabled (i) determination of the time point for the onset of nucleation and (ii) the evolution in particle size to be monitored during the MMA polymerization. The final particle diameters obtained from such TR-SAXS studies were consistent with postmortem DLS analyses, while TEM studies confirmed that near-monodisperse latex particles were formed. Micellar nucleation occurs within just 2 min when the SDS concentration is well above its CMC, resulting in a high particle number concentration and relatively small latex particles. In contrast, when SDS is either absent or present below its CMC, particle nuclei are formed by homogeneous nucleation over significantly longer time scales (14-15 min). In the latter case, adsorption of SDS onto nascent particles reduces their coagulation, giving rise to a larger number of smaller particles compared to the surfactant-free polymerization. However, the characteristic time required for the onset of nucleation is barely affected because this is mainly controlled by the kinetics of homogeneous polymerization of the relatively water-soluble MMA monomer within the aqueous phase. These results suggest that the aqueous emulsion polymerization of several other (meth)acrylic monomers, and perhaps also vinyl acetate, may be amenable to TR-SAXS studies.

Vivid structural colors of photonic crystals: Self-assembly of monodisperse silica nano-colloids synthesized using an anionic surfactant

Photonic crystals are widely applied in non-fading structural color production areas owing to their easy tunability. However, it is found that achieving high monodispersity in the case of particles diameter less than ∼100 nm is challenging. The understanding on the mechanism behind the synthesis could help to fabricate photonic crystals. Here we examine the effect of single anionic surfactant on the final particle diameter. Subsequently, the fabrication of photonic crystals using various size silica nanoparticles ranging from ∼250 nm to ∼50 nm by spin coating method is performed. Vivid structural colors from red to blue are obtained as a function of increasing particle size. This is rather peculiar since most studies shows opposite trend. Furthermore, the colloidal photonic crystals are prepared using spin coating method. The obtained spin coated photonic crystal films exhibit low viewing angle dependent structural colors.

Drying of a single droplet of dextrin: Drying kinetics modeling and particle formation.

Powder production by spray drying is achieved through the dehydration of droplets. The physical properties of the dried powder often influence its application. The drying kinetics of a single droplet of dextrin solution into the solid phase were monitored during the drying process. An acoustic levitator was used to suspend the droplet in the acoustic field. Such experiments are essential for achieving a fundamental understanding of the drying process. Droplets with different initial solid content (dextrin aqueous solution of 10% and 30%) were investigated at different gas drying temperatures. The drying curves were compared to the Reaction Engineering Approach (REA) model. A good agreement between the model prediction and the experimental results was demonstrated, with an absolute relative error of about 2% between the initial droplet mass and the droplet mass that the REA model predicted. The final particle diameter was estimated theoretically and compared to the experimental data. Single droplet simulations have enormous potential for drying step characterization of expensive compounds and highly potent drugs, due to the low amounts that the experiments require.

Soot morphology and nanostructure in complex flame flow patterns via secondary particle surface growth

While the majority of studies explore soot formation in relatively simple, one-dimensional flames, most real-world flames consist of complex flows defined by large-scale turbulent eddies, recirculating flow patterns, and buoyancy effects. The effects of complex flow on soot physicochemical properties are poorly understood. This work employs an inverted gravity flame reactor (IGFR) to compare differences in soot growth between a one-dimensional laminar diffusion flame and a recirculating flame. Computational fluid dynamics (CFD) and experimental observations show particle oscillations between (i) a rich region with a high concentration of surface growth species, and (ii) a high-temperature oxidation region. Transmission electron microscopy (TEM) shows a significant difference in final primary particle diameter, where the one-dimensional flame produces primary particles 10–25 nm in diameter and the recirculating flame produces primary particles 25–75 nm in diameter. Additionally, larger primary particles from the recirculating flame contain both single and multiple cores. We propose that due to the spheroidal shape of the large primary particles, the secondary surface growth is primarily a result of polyaromatic hydrocarbon (PAH) condensation during re-entrainment of mature soot into the fuel-rich region followed by subsequent liquid layer carbonization in the high-temperature environment of the flame front. The recirculating flow patterns in the IGFR and repeated particle growth/oxidation cycle can serve as a model for soot formation in the large-scale flames with complex flow patterns, such as forest fires, coal fire plants, and other sources.

Microstructural properties and grinding of γ-Al2O3 and coal for environmental applications

ABSTRACTThe amphoteric characteristics of some metal oxides complemented by their chemical microstructures form the basis for their use for environmental engineering applications, e.g., alumina as catalyst and abrasive agents. This paper describes the microstructural properties and grinding behavior of γ-Al2O3 and coal particles in a batch impact mill. By grinding γ-Al2O3 and Hunan coal separately in an impact mill, a grinding process model of two dimensionless groups and is developed using Buckingham Pi theorem to obtain the desired particle morphologies. The properties established in this grinding model as key determinants of the grinding behavior are particle hardness, particle density and milling speed. The milling results confirm that γ-Al2O3 of the HBW 5/100 hardness 247 show higher resistance to grinding than coal of HBW hardness 28, because the final ground particle diameters d0.9 after 30 min milling were 136.6 and 33.4 µm for γ-Al2O3 and coal, respectively. This grinding model is pioneering as the particle hardness contained in the dimensionless group embodies an intrinsic material property which controls grinding and is confirmed to be in agreement with the fragmentation pattern.

Synthesis and Characterization of Core-Shell Magnetic Mesoporous Silica and Organosilica Nanostructures

ABSTRACTInitial results en route toward construction of complex magnetic core-shell silica and organosilica nanotheranostics are presented. Magnetite nanoparticles are synthesized by three different methods and embedded within mesoporous silica and organosilica frameworks by different surfactant-templated procedures to produce three types of core-shell nanoparticles. Magnetite nanoparticles (15 nm in diameter) are embedded within mesoporous silica nanoparticles to produce cell-like material with predominantly one magnetite nuclei-resembling core per nanoparticle, with final particle diameter of ca. 150 nm, specific surface area of 573 m2/g and hexagonally structured tubular pores (2.6 nm predominant diameter), extended throughout the volume of nanoparticles. Two forms of spherical core-shell nanoparticles composed of magnetite cores embedded within mesoporous organosilica shells are also obtained by employing ethylene and ethane bridged organobisalkoxysilane precursors. The obtained nanomaterials are characterized by high surface area (978 and 820 m2/g), tubular pore morphology (2 and 2.8 nm predominant pore diameters), different diameters (386 and 100-200 nm), in case of ethylene- and ethane-composed organosilica shells, respectively. Different degree of agglomeration of magnetite nanoparticles was also observed in the obtained materials, and in the case of utilization of surfactant-pre-stabilized magnetite nanoparticles for the syntheses, their uniform and non-agglomerated distribution within the shells was noted.

Power feed synthesis of pressure-sensitive latex adhesives

Latex particles with the same core composition of poly(MMA-co-ALMA) and different shell compositions of poly(BA-co-AA) were prepared by semibatch emulsion polymerization using ‘power feed’ monomer and chain transfer agent addition methods in the shell layers. The seed stage involved formation of seed particles of 111 nm in diameter with a batch process. After that, two growth stages formed the final particle diameter, dz = 300 nm measured by dynamic light scattering. The gel content and the molecular parameters of the polymer were determined. The adhesive properties including loop tack, peel force and shear resistance were measured according to the FINAT test methods No. 9, 1 and 8. An evaluation was also made for the relationship between pressure-sensitive properties and molecular parameters. Introducing power feed to semibatch emulsion polymerization had no significant effect on the latex preparations and could improve the final conversion and the colloidal stability. The observed particles were grown without significant secondary nucleation. The power feed methods had no effect on the glass transfer temperature (Tg) of the shell layer also. Emulsion polymerization conducted by positive power feed resulted in the formation of longer primary polymer chains at the beginning than that conducted by negative power feed and standard uniform feed, which caused a very high gel fraction. As pressure-sensitive adhesives prepared by using the positive power feed had the highest gel content and strongest core–shell interaction, they exhibited the highest shear resistance, but the lowest tack and peel force.

Generation and droplet size distribution of tracer particles for PIV measurements in air, using propylene glycol/water solution

This work measures the size distribution of the particles exiting a simple-design seeding generator. A simple model for the prediction of the droplet size mean diameter is checked against these measurements, giving good agreement. The main fields of use of these generators include tracer particles based optical measurements like Particle Image Velocimetry (PIV). This investigation provides results against which the performance of different seeding generators, liquids, etc., could be compared, at the exit of the aerosol generator. The developed generic seeding generator is thus suggested as a starting point for a basis for a future scalable standard seeding generator for other researchers investigating the production of aerosols for PIV application.The proposed generator is able to seed flows up to 0.2kg/s with ∼10particles/mm3, under normal operation conditions. Air is injected inside a PG-water (propylene glycol – water) mixture through discharging orifices bubbling in the solution. This liquid presents the advantage of being food-grade and apparently harmless to health. In addition, according to practice it seems that the characteristic time of evaporation of the droplet deposited on surfaces is small, so that there is a cleaning effect that does not exist with other fluids like oils. Droplet size distribution at the outlet of the seeding generator is performed by means of a contemporary laser diffraction analyzer Malvern Spraytech®. Measurements reveal narrow-band, single distribution droplet sizes in the order of 1.5μm; suitable for seeding highly turbulent air flows.The use of dry air to generate particles of PG-water solution is proposed as a way of reducing the final particle diameter by means of water evaporation. Solutions with 60% mass fraction of PG reach sub-micrometric average diameters around 0.9μm at 6barg feeding gauge pressure.The proposed prediction model generalizes the results in an attempt to extrapolate them to other designs or fluids. It is based on the turbulent intensity downstream the nozzle exit and indicates that the discharging orifices depth is secondary in respect to the mean droplet diameter obtained.The study also shows that the volumetric concentration of the tracer particles in the generated aerosol is not much sensitive to feeding air pressure. Once the mean droplet size has been stablished with the previously commented method, this offers the possibility of estimating the number of particles generated and, thus, establishing design rules or fluid selection criteria for seeding generators or other similar devices. For feeding pressures from 2 to 6barg, particle quantity generation is in the order of 108particles/s per ∅ 0.5mm nozzle.

Synthesis, characterization and in vitro effects of 7 nm alloyed silver–gold nanoparticles

Alloyed silver–gold nanoparticles were prepared in nine different metal compositions with silver/gold molar ratios of ranging from 90:10 to 10:90. The one-pot synthesis in aqueous medium can easily be modified to gain control over the final particle diameter and the stabilizing agents. The purification of the particles to remove synthesis by-products (which is an important factor for subsequent in vitro experiments) was carried out by multiple ultracentrifugation steps. Characterization by transmission electron microscopy (TEM), differential centrifugal sedimentation (DCS), dynamic light scattering (DLS), UV–vis spectroscopy and atomic absorption spectroscopy (AAS) showed spherical, monodisperse, colloidally stable silver–gold nanoparticles of ≈7 nm diameter with measured molar metal compositions very close to the theoretical values. The examination of the nanoparticle cytotoxicity towards HeLa cells and human mesenchymal stem cells (hMSCs) showed that the toxicity is not proportional to the silver content. Nanoparticles with a silver/gold molar composition of 80:20 showed the highest toxicity.

Advanced Chemistry Surrogate Model Development within C3M for CFD Modeling, Part 1: Methodology Development for Coal Pyrolysis

A generalized method was developed to implement complex chemistry from third-party computational coal chemistry tools within multiphase, reacting computational fluid dynamic (CFD) codes. This method involves generating response surfaces that represent the computational coal chemistry tool output and using them to build a comprehensive surrogate model which can be easily incorporated into a CFD code. In this first part of a series of work, the method was applied to coal pyrolysis of Powder River Basin coal using PC Coal Lab (PCCL) and Carbonaceous Chemistry for Computational Modeling (C3M) to generate the series of response surfaces which form the basis of the surrogate model that can be implemented in CFD. This method has the benefit that local environmental variables (such as heating rate, final pyrolysis temperature, local pressure, and particle diameter) can be incorporated as part of the chemistry model in CFD on a cell by cell, time step by time step basis which creates the potential to significantly...

Growth Mechanism of Monodisperse Spherical Particles under Nanosecond Pulsed Laser Irradiation

It is well-known that the colloidal nanoparticles irradiated by laser can be reduced in size. Recently, we demonstrated that at particular experimental conditions, colloidal nanoparticles of different materials can grow under pulse laser irradiation, finally transforming to the near monodisperse submicron spheres. To date, the detailed mechanism of this process was not revealed. In this work, we explore the mechanism of particle growth by applying the particle heating-melting-evaporation model. Our investigations show that the process of particle growth can be divided into two stages. At the initial stage, particle agglomeration is the dominant factor for the fast particle growth. Then, the process continues as long as the particles can be melted. The final particle diameter is determined by the value of laser fluence, because the laser fluence determines the maximum diameter of the particle which can be melted. Good agreement between the experimental results and results of calculation was obtained.

Nanoprecipitation of polymers in a bad solvent

Nanoparticles (NPs) composed of polymers are of great interest since they can add a functionality in many applications, ranging from food and pharma to plastics and electronics. A key factor that determines the functionality of NPs is their size. Nanoprecipitation [1] is a commonly used technique to prepare NPs. We have performed a combined experimental and theoretical study on the size of NPs formed by precipitation of polymers into a bad solvent in the presence of a stabilizing surfactant.We propose an extension of the theoretical framework put forward by Lannibois et al. [10] for nanoparticle formation via precipitation. Our theory is based upon a kinetic model for diffusion limited coalescence (DLC) in which the relevant transport and diffusion mechanisms are quantified. We find that the macroscopic mixing time and the diffusivity of the polymer and surfactant are the main parameters determining the final particle size. The theoretical result for the final size can be condensed into a single analytical expression. At given polymer concentration and mixing time, it follows that the smallest particles can be obtained in the excess of surfactant. This situation corresponds well to the experimentally used conditions. The mixing efficiency is predicted to have a profound influence on the final particle diameter: faster mixing results in smaller particles. The final particle size in the slow mixing regime, which is the typical situation in experiments, turns out to be independent of the molar mass of the polymer and scales as a power 1/3 with the initial polymer concentration. An increase of the surfactant molar mass is predicted to lead to larger particles, because of longer mixing time and lower surfactant mobility.We have performed systematic experimental investigations on nanoparticles formation using various systems but focused on polycaprolactone (PCL) polymers in acetone precipitated in aqueous solutions containing polyvinyl alcohol as surfactant. The PCL molar mass and concentration and mixing time were varied. We show that both our experimental results as well as literature data are in good agreement with our theoretical DLC predictions. This work therefore provides a solid framework for tailoring nanoparticles with a desired size.

Polyglycidol - how is it synthesized and what is it used for?

This paper presents a short review on the synthesis and properties of polyglycidol(PGL) and its derivatives and on selected medical applications of polyglycidol-containing materials. These materials are often used in the fabrication of medical diagnostic tests and biosensors as well as in bioseparation, biocatalysis and drug delivery systems. Various methods for the polymerization of glycidol (cationic, anionic) are described. Regardless of the synthesis method, each glycidol polymerization process yields branched macromolecules. However, glycidol with protected hydroxyl group can be anionically polymerized, which yields linear polyglycidol after deprotection of the hydroxyl groups. Modifications of the polyglycidol hydroxyl side and end groups and the syntheses of polyglycidol-containing copolymers with various architectures are discussed. A macromonomer, the polyglycidol derivative, -tert-butoxy- -vinylbenzyl-polyglycidol was used as a surfmer in emulsion polymerization of styrene in water. This synthesis method produces core-shell microspheres [P(S/PGL)] that possess a very low (usually less than 1.06) diameter dispersity parameter Dw/Dn (where Dw and Dn denote the weight and number average diameters, respectively). The relationships between the concentration of macromonomer in the polymerization mixture and the concentration of polyglycidol in the particle interfacial layer, final particle diameters and the suitability of the particles for binding biomolecules are discussed. Selected applications of the polyglycidol macromonomer and P(S/PGL) microspheres for the preparation of some materials are described.

In situ and time resolved nucleation and growth of silica nanoparticles forming under simulated geothermal conditions

Detailed knowledge of the reaction kinetics of silica nanoparticle formation in cooling supersaturated waters is fundamental to the understanding of many natural processes including biosilicifcation, sinter formation, and silica diagenesis. Here, we quantified the formation of silica nanoparticles from solution as it would occur in geothermal waters. We used an in situ and real-time approach with silica polymerisation being induced by fast cooling of a 230°C hot and supersaturated silica solution. Experiments were carried out using a novel flow-through geothermal simulator system that was designed to work on-line with either a synchrotron-based small angle X-ray scattering (SAXS) or a conventional dynamic light scattering (DLS) detector system. Our results show that the rate of silica nanoparticle formation is proportional to the silica concentration (640 vs. 960ppm SiO2), and the first detected particles form spheres of approximately 3nm in diameter. These initial nanoparticles grow and reach a final particle diameter of approximately 7nm. Interestingly, neither variations in ionic strength (0.02 vs. 0.06) nor temperature (reactions at 30 to 60°C, mimicking Earth surface values) seem to affect the formation kinetics or the final size of the silica nanoparticles formed. Comparing these results with our previous data from experiments where silica polymerisation and nanoparticle formation was induced by a drop in pH from 12 to near neutral (pH-induced, Tobler et al., 2009) showed that (a) the mechanisms and kinetics of silica nanoparticle nucleation and growth were unaffected by the means to induce silica polymerisation (T drop or pH drop), both following first order reactions kinetics coupled with a surface controlled reaction mechanism. However, the rates of the formation of silica nanoparticles were substantially (around 50%) slower when polymerisation was induced by fast cooling as opposed to pH change. This was evidenced by the occurrence of an induction period, the formation of larger critical nuclei, and the absence of particle aggregation in the T-induced experiments.

Preparation of Melamine Molecularly Imprinted Polymeric Microspheres by Two-Step Seed Swelling Polymerization

Melamine molecularly imprinted polymeric microsphere (MIPM) was initially prepared by two-step seed swelling polymerization methods. Factors affecting the particle morphologies including emulsifier, dispersant, the water-oil ratio, and etc were optimized in order to obtain the MIPMs with a final narrow particle diameter of 3-5 μm. Characterization of the resulted polymeric microspheres was investigated by scanning electron microscope (SEM), infrared absorption spectroscopy (IR), and mercury analyzer (MA), respectively. When the initial concentration of melamine was 1.0 mmol L-1, the affinity capacity of MIPMs was 2.0 times than that of NIPMs. Scatchard analysis suggested melamine were recognized by the prepared MIPMs with two classes of binding sites. The apparent maximum binding capacity and dissociation constant were calculated to be 43.2 μmol g-1 (Qmax1) and 2.2×10-4 mol L-1 (Kd1) for high affinity site, whilst to be 102.3 μmol g-1 (Qmax2) and 1.3×10-3 mol L-1 (Kd2) for low affinity site, respectively. Obvious molecular effects towards melamine were further confirmed by the comparative HPLC experiments using NIPMs and MIPMs as the stationary phases, respectively.

Effects of ultrasound on the synthesis of silicalite-1 nanocrystals

Application of power ultrasound, offers potential in the degree of control over the preparation and properties of nanocrystalline zeolites, which have become increasingly important due to their diverse emerging applications. Synthesis of silicalite-1 nanocrystals from a clear solution was carried out at 348K in the absence and presence of ultrasound of 300 and 600W, in an attempt to investigate the effects of sonication, in this respect. Variation of the particle size and particle size distribution was followed with respect to time using a laser light scattering device with a detector set to collect back-scattered light at an angle of 173°. Product yield was determined and the crystallinity was analyzed by X-ray diffraction for selected samples collected during the syntheses. Nucleation, particle growth and crystallization rates all increased as a result of the application of ultrasound and highly crystalline silicalite-1 of smaller average particle diameter could be obtained at shorter synthesis times. The particle size distributions of the product populations, however, remained similar for similar average particle sizes. The rate of increase in yield was also speeded up in the presence of ultrasound, while the final product yield was not affected. Increasing the power of ultrasound, from 300 to 600W, increased the particle growth rate and the crystalline domain size, and decreased both the final particle diameter and the time required for the particle growth to reach completion, while its effect on nucleation was unclear.

EFFECT OF REACTOR PRESSURE ON PRODUCTION OF ALUMINUM NANO-POWDER

In this paper aluminum nano-powder was produced by evaporation and condensation in a low pressure argon gas atmosphere. The process was modified according to the argon pressure to decrease the aluminum nano-particle size. Therefore, the argon gas pressure was changed from 0.1 to 1 mbar by change of injection flow rate, while other parameters were maintained constant. To evaluate the morphology of produced nano-powders at each argon pressure, the nano-powders were analyzed by Brunauer- Emmett- Teller (BET) method and transmission electron microscopy (TEM). It was found that the final particle diameter decreased with argon pressure. This decrease of particle size reaches a minimum of 85 nm, which corresponds to the pressure of 1 mbar. This powder had a specific surface area of 26.22 m2g-1.

Copper oxide nanoparticle made by flame spray pyrolysis for photoelectrochemical water splitting – Part I. CuO nanoparticle preparation

Copper oxide (CuO) semiconductor nanoparticles are of interest because of their promising use for electronic and optoelectronic devices, and the size of the CuO particles for these applications is important. In this work, near spherical CuO nanoparticles with aspect ratio of 1.2–1.3 were made by a flame spray pyrolysis (FSP) method. In FPS, flame temperature, residence time, precursor concentration can be used to control particle size. As the precursor concentration increased from 0.5% to 35% w/w, primary particle diameter increased from 7 ± 2 to 20 ± 11 nm. Larger primary particle diameters were observed in the low gas flow system (set B) due to the long residence time in the high temperature zone. For the dependence of temperature on particle diameter, particles grew to similar diameter, i.e. ∼11 nm, in both flame conditions within the hot temperature zone (80% of melting point of CuO) but for particles having longer residence time, i.e. 550 ms in set B, the standard deviation of particle diameter is 45% larger than for particles with 66 ms as residence time in set A. Modeling gave a result for CuO final particle diameter, based on collision/sintering theory with sintering by solid state diffusion, of 6.7 and 9.0 nm for set A and set B, respectively, with surface tension assumed to be 0.5 J/m2.Comparison with the experiment results, 11 ± 4 nm diameter for both flame conditions, indicates the simulations were reasonable.

Stöber silica particles as basis for redox modifications: Particle shape, size, polydispersity, and porosity

The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600°C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol–gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques.