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Syntheses of colloids and nanostructured materials

Colloidal silica spheres

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Monodisperse silica spheres are synthesized in a size range between 40 and 1000 nm. These particles can be modified in several ways. Fluorescent molecules can be covalently bond into the particles and an additional silica layer can be grown around existing particles (so called seeded growth). In this way for instance, one can make silica particles with a fluorescent core coated with a non-fluorescent layer of silica. Also several coating procedures can be applied to the silica to change the compatibility of the particles with all kinds of solvents and other materials. Also the interaction potential between the particles can be tuned by applying different surface coatings. Several modifications of these particles are used as model particles in other studies. Recently, new poly(ethylene glycol)-grafted colloidal silica particles with improved stability in aqueous solvents have been synthesized.

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( J. Buitenhuis )


PEG grafting of colloidal silica

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The known grafting procedures of colloidal silica particles with poly(ethylene glycol) (PEG) lead to grafting layers that detach from the silica surface and dissolve in water within a few days. We present a new grafting procedure of PEG onto silica with an improved stability of the grafting layers in aqueous environment. Moreover, the procedure avoids any dry states or other circumstances leading to strong aggregation of the particles. To achieve the improved water stability, the silica particles are first pre-coated with a mixture of organosilane compounds, prior to the PEG grafting. Maybe the pre-coating applied in this study is also of interest to improve the water stability in some biomedical or biological applications where specific molecules are linked to a silica surface by silane coupling agents.

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( J. Buitenhuis )


Fd viruses and other colloidal rods

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Colloidal dispersions of rod-like boehmite particles can be synthesized with a length between 100 and 500 nm. Coating these boehmite particles with silica allows tuning the diameter, improving its polydispersity in width and using the silica chemistry to modify the rods. Even more monodisperse colloidal rods or fibers are fd viruses, which have a length of 880 nm, a width of 6.6 nm and a persistence length of 2.2 µm. These dispersions are used as model particles in several other studies such as shear banding.

 more about Fd virus (PDF, 197 kB)

 more about other colloidal rods (PDF, 227 kB)

( J. Buitenhuis )

Silica coated fd viruses

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Work is in progress on the preparation of silica nanorods using fd viruses as template, to obtain very monodisperse colloidal rods with a high aspect ratio, a tunable diameter and which can be modified with the known silica chemistry.

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( J. Buitenhuis )


Charge reversed fd viruses

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We prepared new charge reversed dispersions of fd viruses (i.e. positively charged at pH 8) by chemical modification of the surface of the viruses. As expected, adding dispersions of positively charged and negatively charged fd together results in flocculation (see left tube compared to right tube showing fd without flocculation). These modified fd dispersions might be of interest as a model system in physical studies on polyelectrolyte effects as well as in material chemistry where the positively charged fd virus might be used e.g. as a template for the preparation of silica nanorods.

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( J. Buitenhuis )



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