Nanojewels made easy

"These nanojewels can potentially find application in photonics, drug delivery, special coatings, sensors and microfluidics," Velev explains.

Indeed, many researchers around the world are working on ways to make similar two-dimensional and three-dimensional photonic crystals to fabricate light-emitting diodes, optical fibers for communications, submicroscopic lasers, ultrawhite pigments, antennas and reflectors, and optical integrated circuits.

The biggest stumbling blocks in making these materials is finding ways of making photonic crystals with uniform properties in very large quantities and in minimizing imperfections in structure that reduce the quality of the final product.

This new process is certainly easy to replicate to make large quantities, and superhydrophobic surfaces lead to structures that naturally form ordered structures.

Superhydrophobic surfaces allow nanojewels to be created from a single drop of water containing nanoparticles, because of several effects.

First, the drop stays in the shape of a ball because water does not spread on it while the nanoparticles are held in the drop due to the surface tension of water.

Compared to drying the drop in air, which is a fast evaporation process that causes the water in the drop to distort and flow, the drop gently dries on the superhydrophobic surface. This lets the nanoparticles get as close to each other as possible, swirling in a slow circular motion until all of the water evaporates.

When nanoparticles of two different sizes are used in the same drop, the smaller ones move to the surface of the drop while the bigger ones stay in the middle. This is because the smaller ones have more Brownian motion and are elevated to the surface with the water molecules that are subsequently evaporating at the surface, leaving all of the nanoparticles behind to form the nanojewels.

"Besides the dazzling look of these nanojewels, the most exciting thing about this work is that it opens up many interesting possibilities in quickly and inexpensively making new materials with nanoparticles", Marquez says.

"By understanding how different particle sizes determine the colors produced, these nanojewels can be designed for applications in optical communication systems," Melle adds.

As more nanoparticles and nanostructures come into the marketplace, technologies that can quickly assemble the structures so that their unique size and properties can be employed in new devices will be important to the growth of nanotechnology and related industries.

Referenced Article

"Synthesis of Light-Diffracting Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface", Vinayak Rastogi, Osca G. Calderon, Antonio A. Garcia, Manuel Marquez, and Orlin Velev, Advanced Materials, (Early View) Published Online 28 Jul 2008 (DOI 10.1002/adma.200703008).

SOURCE:
Antonio Garcia,
Professor, Harrington Department of Bioengineering
Arizona State University
(480) 965-8798

MEDIA CONTACT:
Ira A. Fulton School of Engineering
Arizona State University
Tempe, Arizona USA
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