IIT alumnus offers way to make 'nanojewels' of different colours, optical properties

Washington, July 31 : An Institute of Technology, Roorkee has discerned how different nanoparticles of various sizes can produce "nanojewels" of various colours that display different optical properties.

Vinayak Rastogi conducted this study as a graduate student researcher in the Department of Chemical Engineering at North Carolina State University (NCSU), under the supervision of Professor Orlin Velev.

While making a presentation at the 82nd ACS Colloid and Surface Science Symposium recently, the researchers shed light on potential uses of such nanojewels.

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

The researchers say that colloid chemistry methods, which are originally used to form particle aggregates from nanoparticles, can be used to quickly make particles with dazzling colours simply by letting a suspension of nanoparticles dry on a superhydrophobic surface.

They describe superhydrophobicity as a property of a material that repels water like ducks' feathers or lotus leaves, which has thus far been commercially in textiles, coatings and building materials.

Velev and Rastogi say that superhydrophobic surfaces allow nanojewels to be created from a single drop of water containing nanoparticles, because of several effects.

The researchers say that 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.

According to the researchers, 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.

The researchers say that his happens 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," says Manuel Marquez, an adjunct professor in the Harrington Department of Bioengineering in ASU's Ira A. School of Engineering,

"By understanding how different particle sizes determine the colours produced, these nanojewels can be designed for applications in optical communication systems," adds Sonia Melle, a professor at the School of Optics at UCM.

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.

ANI