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A Nanoparticle in a Nanoscale Volume of Solvent: Thermodynamic and Kinetic Considerations

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journal contribution
posted on 23.10.2008, 00:00 by Wolfram Vogelsberger, Jochen Schmidt
The dissolution behavior of a nanoparticle in a nanoscale volume of solvent was theoretically investigated, using the Gibbs free energy calculation of the system nanoparticle−dissolved material−solvent, as a function of the size of the particle. The chemical nature of the particle is characterized by its surface tension in the solvent and the saturation concentration of the bulk material of the particle-forming species. The influence of both properties on the dissolution behavior was investigated, and the influence of the particle size and the size of the solvent volume was duly considered. The system nanoparticle−dissolved material−solvent is defined, therefore, by four properties. These include the number of molecules of the particle-forming species, the number of solvent molecules, surface tension of the interface particle−solution, and the saturation concentration of the particle-forming species bulk material. Depending on the numerical values of these quantities, a system can exhibit both a critical state (maximum value of Gibbs free energy) and a stable state (minimum value of Gibbs free energy). The dissolution process is finished at the minimum value. It is always possible to discover a system where the minimum and maximum values coincide for a given set of these four properties. These systems are known as first stable states. The first stable states separate regions where the initial particle can form a stable system, nanoparticle−dissolved material−solvent, by dissolution and regions where the nanoparticle dissolves completely. Concentrations of the dissolved material that overcome the equilibrium solubility of the bulk material by several orders of magnitude are possible. The small systems, even with such high concentrations as these, are stable. The results obtained have been confirmed experimentally in relation to multiparticle systems. They are of particular significance when one applies them to the synthesis of nanoscale materials and the valuation of possible toxicity of nanoscale particles.