All-Nanoparticle Coatings Increase Clarity

Michael A. Greenwood

Nanoparticle coatings with antireflective, antifogging and self-cleaning properties have been prepared by a team of researchers from MIT in Cambridge, Mass. Using an aqueous-based layer-by-layer deposition technique, the scientists created thin films of nanoparticles on surfaces. The multilayer coatings comprised oppositely charged nanoparticles (positively charged TiO₂ particles with an average size of ~7 nm and negatively charged SiO₂ particles with an average size of ~7 and ~22 nm) and were applied to glass or silicon substrates.

The image demonstrates the antifogging properties of multilayer-coated glass (left) compared with an untreated glass substrate (right). Reprinted with permission of the American Chemical Society.

Lead researchers Robert E. Cohen and Michael F. Rubner said that, despite decades of study and many breakthroughs, research of films containing oppositely charged nanoparticles without any polyelectrolytes has been more or less neglected.

The results of the current study have a variety of potentially useful applications, including better visibility for motorists. Nanoparticle-based coatings on glass cause the reflective losses in the visible region to be significantly reduced, and transmission levels above 99 percent can be achieved.

The self-cleaning properties of the coatings also have potential applications in photovoltaic cells, vehicle windshields and the windows of high-rise buildings.

Nano Letters, Sept. 9, 2006, published online, doi:10.1021/nl061776m.