Rice Chemists Discover Key To Self-Assembly for Novel Devices
Chemists at Rice University may have unlocked one of the secrets for using nanoscale ābuilding blocksā to assemble much larger superstructures.
Rice researchers have found that tiny building blocks (gold nanorods) will spontaneously assemble themselves into ring-like superstructures. The finding, Rice researchers said, could lead to the development of novel nanodevices such as highly-sensitive optical sensors, superlenses, or even āinvisible objectsā for use in the military.
āFinding new ways to assemble nano-objects into superstructures is an important task because at the nanoscale, the properties of those objects depend on the arrangement of individual building blocks,ā said principal investigator Eugene Zubarev, a Rice assistance professor and the Norman Hackerman-Welch Young Investigator.
Although ring-like assemblies have been observed in spherical nanoparticles and other symmetrical molecules, until now such structures had not been documented with rod-shaped nanostructures.
Inside Riceās Self-Assembly Experiment
Like many nanoscale objects, gold nanorods are several billionths of a meter, or 1,000 times smaller than a human hair. Zubarev used hybrid nanorods for this research because attached to their surface are thousands of polymer molecules, which are flexible chainlike structures. The central core of the nanorods is an inorganic crystal, but the polymers attached to the outside are organic species. The combination of the inorganic and organic features resulted in a hybrid structure that proved to be critical to the study.
Zubarev, working with Rice graduate student Bishnu Khanal, placed the nanorods in a solution of organic solvent called chloroform. As the chloroform evaporated, its surface temperature dropped low enough to cause condensation of water droplets from the air, much like how dew forms. As thousands and thousands of micro-droplets of water formed on the surface of the liquid chloroform, the nanorods that had been suspended in the solution started to press up against the round droplets and form rings around them. The polymer coating prevented the rods from being absorbed into the droplets because it is insoluble in water.
After the droplets evaporated, the nanorods remained in their ring formation. Zubarev said thousands of well-defined rings can be produced in a matter of seconds using the approach from his study. āThis method is surprisingly simpleā¦and can organiz[e] nanocrystalsā¦ into circular arrays.ā When nanorods are organized into a ring, significant changes in their optical and electromagnetic properties occur, Zubarev said. āThese can have technological applications in the area of metamaterials, which have enormous potential in opto-electronics, communications and military applications,ā he said.
This finding, which will be published in Angewandte Chemieās March 19 international edition. The Rice research was funded by the National Science Foundation and the Welch Foundation.