As you probably know, many physical and chemical properties at the nanoscale are quite different from those in either molecular or microscopic regimes. We have recently shown that the common “nano-is-different” belief is very much true for two types of fundamentally important interactions: electrostatic and dipole-dipole. When such forces mediate self-assembly of nanoscopic objects, they lead to very unique organized states of matter: new types of nanostructured crystals (cf. picture below, Science 2006, Nano Lett. 2006 and 2007), semi-crystals, assemblies that organize in response to light (PNAS 2007), and many, many more. One of the most fascinating projects we pursue aims at using charged nanoobjects as analogs of inorganic ions. Unlike with ions, however, we can change the charges on these objects in an almost continuous fashion (cf. JACS 2006 and JACS 2007). With this capability, we can then self-assemble oppositely charged “nanoions” with quite exotic ratios of relative charges Q+/Q-, not seen in ionic crystals. Some of these charge ratios are incommensurate with the point-groups of conventional crystals – as a result, the nanoions form symmetry-broken structures whose intricacy and properties will certainly keep us busy for several years. Stay tuned as this story unfolds!

Nanoparticle supracrystals self-assembled from equal numbers (millions) of oppositely charged, 5 nm gold and silver nanoparticles. These crystals have a diamond lattice structure. The bottom row shows real (i.e., carbon-based) diamond crystals of the same morphologies. (for details, see Science 2006).

 

 

 

 

 

 

Department of Chemical and Biological Engineering | McCormick School of Engineering
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