Silica nanoparticles are common nanoscale components. Polydispersed nanoscale silica is used as a transparent filler in polymers, modifies the flow properties of emulsions and improves the properties of construction materials. With a narrow size distribution, silica nanoparticles can introduce nanoscale regularity on surfaces or in bulk materials either as component of the final material or as an etch mask in further processing steps. In all cases, particle-matrix compatibility and composite behavior depend on the surface chemistry of the particles.Here we address organically functionalized particles, which have found application in many areas including paints and coatings, [1,2] sensors, [3] catalysis, [4,5] and drug delivery methodologies. [6,7] Hydrophobic silica nanoparticles interact strongly with the constituent molecules of the polymer matrix and have been shown to enhance physical and mechanical properties of nanocomposites. [8,9] Assembly of monodispersed silica nanoparticles into regular superstructures is a promising route to materials with rationally designed microstructures. Stable suspensions of hydrophobic silica nanoparticles in apolar solvents are also good model systems for studying the equilibrium and transport properties of colloidal dispersions; their refractive index matches that of some apolar solvents, minimizing multiple scattering in light scattering experiments. [10][11][12] Three solution-based routes to hydrophobic silica nanoparticles are compared in this paper. First, the established synthetic method based on the Stö ber process was examined. Monodispersed colloidal particles with diameters of 15-25 nm were prepared via the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) by aqueous ammonia in ethanol. The surfaces of these particles were rendered hydrophobic with octadecyltrimethoxysilane (ODTMS) after the reaction or, more conveniently, during the growth phase. Secondly, silica particles with diameters of 15-50 nm were prepared using a one-pot synthesis in which TEOS was hydrolyzed by an amino acid and the resulting particles were coated with ODTMS. Lastly a novel, direct approach to the synthesis of hydrophobic organosilica nanoparticles was developed using ODTMS as the single silica source. Hydrolysis of the ODTMS by aqueous ammonia in ethanol yielded monodisperse colloidal organosilica particles with diameters of 15-30 nm.The first approach used here is based on the commonly applied hydrolysis and condensation of tetraalkyl orthosilicates by a strong base as originally developed by Stö ber. [13] The resulting hydrophilic particles can then be modified by the grafting of organosilicate compounds onto their surfaces or by the co-hydrolysis of a tetraorthosilicate with the required functional organosilane. Using these techniques, silica nano-COMMUNICATION [*] Dr. [**] We thank the Physical Analysis Group at INM for technical assistance and Christian Cavelius for scientific discussions. The authors thank Eduard Arzt for his continuing support.Three synthetic routes to...
The ageing of spherical gold nanoparticles having 6‐nm‐diameter cores and a ligand shell of dodecanethiol is investigated under different storage conditions. Losses caused by agglomeration and changes in optical particle properties are quantified. Changes in colloidal stability are probed by analytical centrifugation in a polar solvent mixture. Chemical changes are detected by elementary analysis of particles and solvent. Fractionation occurs under all storage conditions. Ageing is not uniform but broadens the property distributions of the particles. Small‐number statistics in the ligand shell density and the morphological heterogeneity of particles are possible explanations. Washing steps exacerbate ageing, a process that could not be fully reversed by excess ligands. Dry storage is not preferable to storage in solvent. Storage under inert argon atmosphere reduces losses more than all other conditions but could not prevent it entirely.
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