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Ostwald Ripening (ostwald + ripening)
Selected AbstractsEncapsulation and Ostwald Ripening of Au and Au,Cl Complex Nanostructures in Silica Shells,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2006W. Lou Abstract We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle-mediated self-assembly. We have also used the as-prepared multicore Au,silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au,Cl complex is formed inside the shell, and is found to be very active under in,situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in,situ studies of confined crystal growth. [source] Formation and ageing of L-glutamic acid spherulitesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2010R. Beck Abstract Polycrystalline spherulites of L-glutamic acid have been crystallized by pH-shift precipitation from stirred aqueous solutions. The time dependent behaviour of the spherulites has been studied during the crystallization process and batch filtration tests have been performed. It has been shown that the FBRM mean chord length of the investigated spherulites decreases in the course of time. The fact that the size reduction progresses faster at higher temperature and the solubility of resuspended polycrystalline particles decreasing with time, implies an ageing mechanism to be responsible for the observed changes in the particle size. It has been shown that the surface area decreases with time, ruling out particle breakage as a possible explanation for the decrease in particle size. XRD and Raman studies of L-glutamic acid, however, show only marginal differences in the crystalline structure of particles obtained from different time stages. The ageing may occur due to several different mechanisms like phase transformation and Ostwald ripening. L-glutamic acid spherulites after 3 h exhibit a 3-fold higher value for the cake resistance as compared to particles after 0.5 h. However, particles obtained after 22 h exhibit an 8-fold lower cake resistance as compared to the initially obtained spherulites, The increase in the cake resistance is attributed to the appearance of small plate-like crystals and a change in the interaction between the crystal surface and the solution. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydrothermal Syntheses of Gold Nanocrystals: From Icosahedral to Its Truncated Form,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008J. Xu Abstract We have successfully controlled the shape of gold nanocrystals through a simple and low-cost hydrothermal method based on a modified polyol process. Well-defined gold nanocrystals of icosahedral shape were synthesized in high yields by the rapid reduction of gold precursors with ethylene glycol (EG) in the presence of poly(vinyl pyrrolidone) (PVP) under hydrothermal conditions for 1 h. Truncated icosahedra (football-shaped) have been prepared for the first time by prolonging the reaction time to 4 h. Both nanocrystal shapes were obtained quantitatively. Addition of citric acid inhibits the shape-change process (from icosahedron to truncated icosahedron) by blocking oxidative etching, while addition of Fe(III) facilitates the shape-change process by enhancing oxidative etching. We propose that growth of truncated icosahedra can be induced and maintained through interplay of the following processes: generation of multiple twinned seeds, shape- and size-focusing by Ostwald ripening, and oxidative etching and preferential growth on the {100} face. [source] Cobalt Nanoskeletons: One-Pot Solution Synthesis of Cubic Cobalt Nanoskeletons (Adv. Mater.ADVANCED MATERIALS, Issue 16 200916/2009) Cubic Co nanoskeletons with an edge length of 100 nm can be prepared by a facile one-step solution method. In work reported on p. 1636 by Ying Ma, Fangli Yuan, Jiannian Yao, and co-workers, CoO nanoparticles of ,10 nm are subjected to self-aggregating, in situ reduction, Ostwald ripening, and facet-selective coordination-assisted etching to form these novel structures, which exhibit excellent magnetic properties. Simple control of the shape can be achieved by altering the reaction time. [source] Ion beam synthesis of buried Zn-VI quantum dots in SiO2, grazing incidence small-angle X-ray scattering studiesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003I.D. Desnica-Frankovic Grazing incidence small-angle X-ray scattering was used to study ion-beam synthesized Zn-VI compound-semiconductor quantum dots (QDs), buried in a SiO2 matrix. The ZnTe and ZnS QDs were formed by successive ion implantation of constituent atoms, at high ion doses and subsequent annealing at different temperatures in the 1070,1370 K range. In Zn and Te implanted SiO2, small nano-crystals were formed at higher annealing-temperatures, a bimodal size distribution of nano-particles was observed for both materials, which could be explained by an interplay of Ostwald ripening and enhanced diffusion in the irradiation-damaged region. [source] Miniemulsion polymerization of a fluorinated acrylate copolymer: Kinetic studies and nanolatex morphology characterizationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Qinghua Zhang Abstract A stable fluoroacrylate copolymer emulsion was successfully prepared by miniemulsion polymerization with fluoroacrylate, lauryl methylacrylate, and methyl methacrylate as monomers. Extremely hydrophobic fluoroacrylate, instead of conventional cosurfactants, was used as a reactive cosurfactant to stabilize the miniemulsions. The results indicated that fluoroacrylate retarded Ostwald ripening and allowed the production of stable miniemulsions. The chemical compositions of the copolymer were studied with Fourier transform infrared and 1H-NMR. The average composition of the copolymers prepared with miniemulsions was in good agreement with the feed ratio according to 1H-NMR from the integration ratios corresponding to typical protons of the individual monomers. The particle size distribution and morphology of the latex particles were determined with laser particle analysis and transmission electron microscopy. The particle size of the latex underwent no change in the process of miniemulsion polymerization, but the particle size distributions were broader than those of conventional emulsion polymerization. The effects of various reaction parameters, including the temperature and concentrations of the emulsifier and initiator, on the miniemulsion polymerization were also investigated, and the polymerization rate and conversion increased with increasing concentrations of nonylphenol polyethoxylate (with an average of 40 ethylene oxide units per molecule), cetyltrimethylammonium, and 2,2,-azobisisobutyronitrile. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 641,647, 2007 [source] Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentaneJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2005Alison Paul The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21°C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, , = 12 mgg,1) was found to adsorb more strongly than PEG (, = 4 mgg,1). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles. [source] Dynamic Equilibria in Solvent-Mediated Anion, Cation and Ligand Exchange in Transition-Metal Coordination Polymers: Solid-State Transfer or Recrystallisation?CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Xianjin Cui Abstract The solution properties of a series of transition-metal,ligand coordination polymers [ML(X)n], [M=AgI, ZnII, HgII and CdII; L=4,4,-bipyridine (4,4,-bipy), pyrazine (pyz), 3,4,-bipyridine (3,4,-bipy), 4-(10-(pyridin-4-yl)anthracen-9-yl)pyridine (anbp); X=NO3,, CH3COO,, CF3SO3,, Cl,, BF4,; n=1 or 2] in the presence of competing anions, metal cations and ligands have been investigated systematically. Providing that the solubility of the starting complex is sufficiently high, all the components of the coordination polymer, namely the anion, the cation and the ligand, can be exchanged on contact with a solution phase of a competing component. The solubility of coordination polymers is a key factor in the analysis of their reactivity and this solubility depends strongly on the physical properties of the solvent and on its ability to bind metal cations constituting the backbone of the coordination polymer. The degree of reversibility of these solvent-induced anion-exchange transformations is determined by the ratio of the solubility product constants for the starting and resultant complexes, which in turn depend upon the choice of solvent and the temperature. The extent of anion exchange is controlled effectively by the ratio of the concentrations of incoming ions to outgoing ions in the liquid phase and the solvation of various constituent components comprising the coordination polymer. These observations can be rationalised in terms of a dynamic equilibrium of ion exchange reactions coupled with Ostwald ripening of crystalline products. The single-crystal X-ray structures of [Ag(pyz)ClO4], (1), {[Ag(4,4,-bipy)(CF3SO3)],CH3CN}, (2), {[Ag(4,4,-bipy)(CH3CN)]ClO4, 0.5,CH3CN}, (3), metal-free anbp (4), [Ag(anbp)NO3(H2O)], (5), {[Cd(4,4,-bipy)2(H2O)2](NO3)2,4,H2O}, (6) and {[Zn(4,4,-bipy)SO4(H2O)3] ,2,H2O}, (7) are reported. [source] | |||||||||||||