Superparticles Shaped from Nanorods

A new technique for growing complex superparticles from self-assembling nanorods could create a new generation of polarized LEDs.

Joining nanoparticles creates new materials with [enhanced] collective properties. Such materials have the potential to revolutionize applications from data processing to medicine, but attempts to assemble nanoscale objects into sophisticated structures have been largely unsuccessful.

The University of Florida study represents a major breakthrough in the field, showing how thermodynamic forces can manipulate growth of nanoparticles into superparticles with unprecedented precision.

Artistic renderings of a superparticle formed from self-assembling nanorods. Courtesy of Dustin S. LaMontagne.

In the study, a synergism of fluorescent nanorods, sometimes used as biomarkers in biomedical research, resulted in a superparticle with an emission polarization ratio that could make it a good candidate for creating a new generation of polarized LEDs, used in display devices such as 3-D TVs.

“The technology for making the single nanorods is well established,” said Tie Wang, a postdoctoral researcher and lead author of the study, which appeared in Science (doi: 10.1126/science.1224221). “But what we’ve lacked is a way to assemble them in a controlled fashion to get useful structures and materials.”

Individual rods were bathed in a series of liquid compounds that reacted with certain hydrophobic regions on the nanoparticles, pushing them into place to form colloidal superparticles with dimensions ranging from hundreds of nanometers to several microns. The superparticles’ shape is controlled by the number of rods: In smaller numbers, the rods all align in the same direction, whereas a larger number of rods produces capping regions where the rods are perpendicular to those in the core of the superstructure.

Two different treatments yielded two different products.

“One treatment gave us something completely unexpected — these superparticles with a really sophisticated structure unlike anything we’ve seen before,” Wang said. The other yielded a less complex structure that the team grew into a small square of polarized film about one-quarter the size of a postage stamp.

The film could be used to increase the efficiency in polarized LED computer and TV screens by up to 50 percent using currently available manufacturing methods, the chemists said.

For more information, visit: www.chem.ufl.edu