Description

Intuitively, one might expect that when negatively and positively charged nanoparticles are mixed together, they should simply clump together and precipitate. In reality, such nanoparticle mixtures – if prepared carefully -- are extremely stable and persist without precipitation for weeks to months (to learn why, see J. Am. Chem. Soc. 2007, 129, 15623). Although stable by themselves, however, the +/- NP mixtures are destabilized when a piece of another material bearing residual surface charge (e.g., an oxidized piece of a polymer, or a glass slide, or a semiconductor) is immersed into them. Under such conditions, the nanoparticles adsorb cooperatively onto the immersed object, on which they form a dense and durable monolayer coating. This phenomenon allows for covering various types of materials with a monolayer-thick “nanopaint” whose properties derive from those of the constituent nanoparticles. The Boutiqe sells two such “paint” solutions that incorporate antibacterial AgNPs. In the Figure, the orange coatings deposited on small pieces of glass are composed of a mixture of Ag/HS-(CH2)11-N(CH3)3+  and  Ag/ HS-(CH2)10-COO- nanoparticles. Dark-pink coatings (also on glass) comprise Ag/HS-(CH2)11-N(CH3)3+  and  Au/ HS-(CH2)10-COO- .