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Particular nanoparticles
Birds of a feather flock together, is what they say about human beings. Up to now, the same seemed to apply to nanoparticles. However, a research group headed by the Bielefeld chemist Professor Dr. Achim Müller together with colleagues in the United States has been able to confirm that such particles can be rather particular: even just the small change of dissolving them in water leads the originally equal-sized and identically shaped particles to no longer merge together when they meet, but to form two separate blackberry-like structures. The scientists published the results of this research in the prestigious journal Science, Vol. 331, at the end of March 2011.
Professor Dr. Achim Müller and Professor Dr. Tianbo Liu from Lehigh University, Bethlehem Pennsylvania report the outcome of their studies under the title Self-Recognition Among Different Polyprotic Macrioions During Assembly Processes in Dilute Solution. The article deals with equally large spherical nanoparticles that originally show the same charge density and surface structure (Figure B). Like a ‘nano water ball’, their surface consists purely of water molecules and oxygen atoms. When these particles are dissolved in water, however, strange things happen: instead of merging together into one structure as anticipated, two separate blackberry-like structures form that each exhibit only one type of particle (Figure C). What makes this process possible is the various metallic atoms (namely, iron and chrome) positioned directly below the surface of the nanospheres. These differ in the way they influence the water molecules located above them. As a result, not only the residence times of the surface water molecules but also their so-called ‘proton donor’ property – that is, their ability to donate hydrogen atoms – differ by several magnitudes. This gives the nanospheres different electrical charges that leads to the segregation of the ‘chemical blackberries’ and their different sizes.
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Internet, go to
www.sciencemag.org/content/331/6024/1590.full