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Universal solvent restructuring induced by colloidal nanoparticles

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Science  16 Jan 2015:
Vol. 347, Issue 6219, pp. 292-294
DOI: 10.1126/science.1261412

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Structured solvents near nanoparticles

The physical properties and reactivity of nanoparticles in solution depend not only on their surface termination but also on changes in solvent ordering caused by the presence of the interface created by the nanoparticle. Zobel et al. used x-ray scattering to study solvent ordering for a variety of metal and metal-oxide nanoparticles in a variety of polar solvents (alcohols) and a nonpolar solvent (n-hexane). They observed layers of enhanced ordering near the nanoparticle surface relative to the bulk solvent. These trends were largely independent of surface chemistry, such as changing the surface groups from hydroxyls to carboxylates.

Science, this issue p. 292

Abstract

Colloidal nanoparticles, used for applications from catalysis and energy applications to cosmetics, are typically embedded in matrixes or dispersed in solutions. The entire particle surface, which is where reactions are expected to occur, is thus exposed. Here, we show with x-ray pair distribution function analysis that polar and nonpolar solvents universally restructure around nanoparticles. Layers of enhanced order exist with a thickness influenced by the molecule size and up to 2 nanometers beyond the nanoparticle surface. These results show that the enhanced reactivity of solvated nanoparticles includes a contribution from a solvation shell of the size of the particle itself.

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