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Researchers led by Prof. Dr. Matthias Karg at the Institute of Physical Chemistry report a simple technique for developing highly ordered particle layers. The group worked with tiny, deformable spherical polymer beads with a hydrogel-like structure. Hydrogels are water-swollen, three-dimensional networks. Such structures are used as super-absorbers in such products as babies' nappies due to their ability to soak up large quantities of liquids.
Within these hydrogel beads are tiny gold or silver particles just a few nanometres in size, which Karg's team synthesizes at HHU using metal salts in a reduction process. "We can adjust the size of the gold particles very precisely because the hydrogel shells are permeable to dissolved metal salts, allowing for successive overgrowth of the gold cores." The structure of these core-shell particles can be roughly compared to that of a cherry, in which a hard core is surrounded by soft pulp.
Researchers - Solution - Hydrogel - Beads - Monolayers
The Duesseldorf-based researchers used a dilute solution of these hydrogel beads to produce thin monolayers. They applied the beads to a water surface, where a shimmering, highly ordered layer self-assembled. The researchers transferred this layer from the water surface onto glass substrates; this transfer makes the glass substrate shimmer.
Looking at such a layer with an electron microscope reveals a regular, hexagonally ordered particle array. "These are the gold particles in their shells," explains doctoral...
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