Browsing by Subject "Ostwald ripening"
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Item Open Access Mesoscopic model of nucleation and Ostwald ripening/stepping: Application to the silica polymorph system(American Inst of Physics, Woodbury, NY, United States, 2000) Ozkan, G.; Ortoleva, P.Precipitation is modeled using a particle size distribution ~PSD! approach for the single or multiple polymorph system. A chemical kinetic-type model for the construction of the molecular clusters of each polymorph is formulated that accounts for adsorption at a heterogeneous site, nucleation, growth, and Ostwald ripening. When multiple polymorphs are accounted for, Ostwald stepping is also predicted. The challenge of simulating the 23 order of magnitude in cluster size ~monomer, dimer, . . . , 1023-mer! is met by a new formalism that accounts for the macroscopic behavior of large clusters as well as the structure of small ones. The theory is set forth for the surface kinetic controlled growth systems and it involves corrections to the Lifshitz–Slyozov, Wagner ~LSW! equation and preserves the monomer addition kinetics for small clusters. A time independent, scaled PSD behavior is achieved both analytically and numerically, and the average radius grows with Rave}t1/2 law for smooth particles. Applications are presented for the silica system that involves five polymorphs. Effects of the adsorption energetics and the smooth or fractal nature of clusters on the nucleation, ripening, and stepping behavior are analyzed. The Ostwald stepping scenario is found to be highly sensitive to adsorption energetics. Long time scaling behavior of the PSD reveals time exponents greater than those for the classical theory when particles are fractal. Exact scaling solutions for the PSD are compared with numerical results to assess the accuracy and convergence of our numerical technique. © 2000 American Institute of Physics. @S0021-9606~00!70123-1#Item Open Access Theories of nanoparticle and nanostructure formation in liquid phase(Elsevier, 2018) Karatutlu, A.; Barhoum, A.; Sapelkin, A.Nanoparticles (NPs) and nanostructured materials exhibit shape- and size-dependent properties that are desired for a wide variety of applications, such as catalysis, sensing, drug delivery, energy production, and storage. In view of this, it is essential to produce well-defined NPs and nanostructures with desired characteristics, to understand their formation and growth mechanisms, and to define the critical size below which they act differently from bulk materials in order to develop synthetic strategies. For example, quantum dots (below 20nm) are mainly single nanocrystals characterized by a single-domain crystalline lattice without grain boundaries. These tiny individual crystals differ drastically from bulk polycrystalline materials. In fact, existing investigations indicated that ordered polycrystalline particles are preferably formed at high supersaturations, where rapid nucleation generates many NPs, which subsequently tend to aggregate randomly at high NP concentrations. Single crystals, such as quantum dots, form at low supersaturations. The reduction of the supersaturation to a level at which primary NPs are still formed in solution yields mesocrystals. This chapter discusses the advanced nucleation and growth theories that are used to explain the growth of the obtained nanoparticles and nanostructures to the desired structures.