Quantification of initial steps of nucleation and growth of silica nanoparticles: An in-situ SAXS and DLS study
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Small-angle X-ray scattering
Ostwald ripening
Particle (ecology)
This work aims to evaluate the effect of Ostwald ripening on the crystallization of polymorphic phases by means of the kinetic equation model, which was adapted to describe the competition between the nucleation, the growth, and the Ostwald ripening of the different phases. The kinetic equation model is a very convenient way to simultaneously implement these three mechanisms and quantify their respective roles on the formation and the dissolution of the clusters. The polymorphic system studied is l-glutamic acid (LGlu), which exhibits two monotropic polymorphs: α LGlu and β LGlu. The model assumptions consider the main differences between both polymorphs (shape, solubility, interfacial energy, and growth rate) as well as the supersaturation decrease. The simulation results at various temperatures show that the crystallization process of small nuclei (<40 nm) can be greatly affected by the Ostwald ripening mechanism. In particular, Ostwald ripening can induce the total dissolution of the stable phase clusters, leading to a result in agreement with the Ostwald rule of stages. Thus, the numerical results suggest that the Ostwald ripening mechanism could explain the Ostwald rule of stages.
Ostwald ripening
Supersaturation
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Abstract The Ostwald ripening of crystalline precipitates in aqueous solutions is measured, the systems being H 2 O‐NaNO 3 and H 2 O‐Tetraethyl‐ammoniumiodide (TEAI). By comparison of the results at constant temperature with the theory, it is found that the growth kinetics of both substances seems to be determined by a second order reaction. For the application of Ostwald ripening in preparative chemistry and chemical engineering, it is suggested to age the precipitate at periodically changing temperature. This leads to an increase of the aging rate by more than one order of magnitude. The dependence of this increase on frequency and amplitude of the temperature changes is measured.
Ostwald ripening
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A facile synthesis method was developed based on the seed-mediated growth to get the narrow dispersed silver nanoparticles with controllable sizes ranging from 20 nm to larger than 120 nm. Environmentally friendly glucose acts as a reducing agent. Because of its weak reducing ability, the secondary nucleation is prevented in the seed-mediated growth, and the size of silver nanoparticles can be tuned continuously by the continuous addition of reactants. Controlling the supersaturation level is critical to suppress both the nucleation and Ostwald ripening, which can be realized by carefully controlling the addition rate of the reactants. We also set up a convenient method to determine the size and size-distribution of silver nanoparticles from the size-dependent absorption spectra of the colloids, and optimize the growth parameters using this method to get narrow dispersed silver nanoparticles.
Ostwald ripening
Supersaturation
Silver nanoparticle
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The formation of stable transparent nanoemulsions poses two challenges: the ability to initially create an emulsion where the entire droplet size distribution is below 80 nm, and the subsequent stabilization of this emulsion against Ostwald ripening. The physical properties of the oil phase and the nature of the surfactant layer were found to have a considerable impact on nanoemulsion formation and stabilization. Nanoemulsions made with high viscosity oils, such as long chain triglycerides (LCT), were considerably larger ( D = 120 nm) than nanoemulsions prepared with low viscosity oils such as hexadecane ( D = 80 nm). The optimization of surfactant architecture, and differential viscosity eta D/eta C, has led to the formation of remarkably small nanoemulsions. With average sizes below 40 nm they are some of the smallest homogenized emulsions ever reported. What is more remarkable is that LCT nanoemulsions do not undergo Ostwald ripening and are physically stable for over 3 months. Ostwald ripening is prevented by the large molar volume of long chain triglyceride oils, which makes them insoluble in water thus providing a kinetic barrier to Ostwald ripening. Examination of the Ostwald ripening of mixed oil nanoemulsions found that the entropy gain associated with oil demixing provided a thermodynamic barrier to Ostwald ripening. Not only are the nanoemulsions created in this work some of the smallest reported, but they are also thermodynamically stable to Ostwald ripening when at least 50% of the oil phase is an insoluble triglyceride.
Ostwald ripening
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Since the process of coarsening, the growth of the mean radius of the clusters of a new phase in solutions connected with a decrease of their number was described and discussed first by OSTWALD (1901), such a process is widely denoted as Ostwald ripening (LIESEGANG, 1911).
Ostwald ripening
Critical radius
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Abstract Tremendous focus has been put on the control of particle size distribution which effects the grain structure and mechanical properties of resulting metallic materials, and thus nucleation and growth of particles in solution should be clarified. This study uses classical nucleation theory and Ostwald ripening theory to probe the relationship between the compositions of Fe-O-Al-Ca melts and the behavior of particles under the condition of no external stirring. Our experimental data suggest that decreasing the initial Ca addition and Al addition is conductive to the increase of nucleation rate for calcium aluminate particles, which exhibits a same change trend with that predicted from classical nucleation theory. Based on the experimental evidence for particles size distribution in three-dimensional, we demonstrate that Ostwald ripening is the predominate mechanism on the coarsening of particles in Fe-O-Al-Ca melt at early stage of deoxidation under the condition of no external stirring but not at later stage.
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This paper presents textural evolution of metamorphic rocks due to Ostwald ripening. First, Crystal size distributions (CSDs) of garnets in various metamorphic rocks are compared with the LSW (Lifshitz-Slyozov-Wagner) distribution for Ostwald ripening. There are two types of CSD. One is consistent with LSW distribution, the other is wider than LSW distribution. The former one has a homogeneous spatial disposition of garnets, and represents the progress of Ostwald ripen-ing. That CSD of the latter type is wider than LSW, is either; 1) because duration of Ostwald ripening is not sufficient, or 2) because spatial disposition of garnets is not homogeneous. LSW theory needs homogeneous spatial disposition of precipi-tated phase. Ostwald ripening in spatially heterogeneous system is researched by numerical simulation. The results suggest that heterogeneous structure, such as layered structure, are developed by Ostwald ripening. Shape of size distribution is important in two reasons; 1) material transport between layers by Ostwald ripening can be evaluated by comparisons of size distributions between layers, and 2) the width of initial size distribution strongly influences an evolution of layering structure.
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Basic Equations: Determination of the Coefficients of Emission in Nucleation Theory Kinetics of Nucleation-Growth Processes: The First Stages Theory of the Late Stages of Nucleation-Growth Processes: Ostwald Ripening Shapes of Cluster Size Distributions Evolving in Nucleation and Growth Processes Coarsening under the Influence of Elastic Stresses and in Porous Materials
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Growth theory
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A growth mechanism for single crystalline hollow spheres was proposed based on the study of the formation process of single crystalline Cu2O multishelled hollow spheres. On the basis of transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction analysis of the product collected at different formation stages, it is found that the nanoparticles with a size of 2−5 nm first formed well-crystallized porous shelled hollow spheres via oriented attachment, and then the porous shells were further crystallized and became compact by Ostwald ripening to form well-crystallized hollow spheres.
Ostwald ripening
Morphology
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A study by small angle X-ray scattering (SAXS) on the AlLiMg system is reported. Size distribution functions of GP zones in the growth stage are determined without imposing any a priori functional shape. As a result, an Ostwald ripening mechanism for the coarsening process can be inferred from the shape of the resulting particle size distribution. Ein AlLiMg-System wird mit Kleinwinkelstreuung (SAXS) untersucht. Es werden Verteilungsfunktionen für Guinier-Preston-Zonen im Wachstumsstadium bestimmt, ohne einen a priori Funktionsverlauf festzulegen. Als Resultat kann aus der Art der sich ergebenden Partikelgrößenverteilung ein Ostwald-Reifungsmechanismus für den Wachstumsprozeß angenommen werden.
Ostwald ripening
Small-angle X-ray scattering
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