Some, Like Russian Dolls, Fit Inside Each Other: Self-Assembled Nanospheres May Be Helpful Against Disease Or Terrorism, Or As Fillers And Coatings

According to one reviewer, the spheres demonstrate an unprecedented control over organic and inorganic nanoscale self-assemblies, and represent a major step forward in control of these techniques.

The durable silica spheres, which range in size from 2 to 50 nanometers, form in a few seconds, are small enough to be introduced into the body, and have uniform pores that enable controlled release of drugs. The spheres can absorb organic and inorganic substances including small particles of iron, which means they can be controlled by magnets and the contents released as needed.

The small porous particles also have characteristics superior to fillers used in encapsulants for weapons and tools. The expansion coefficients of polymers and the metallic devices they cradle usually differ substantially. This means that temperature variations cause the encapsulants to stress the devices they are meant to protect. The induced stresses can decrease longevity of a device. Nanosphere fillers would occupy the same volume, but because they are porous can expand and contract with much less stress.

Lastly, the Sandia nanospheres may be useful as coatings on silicon chips whose increasingly tiny circuits require a medium that has a lower dielectric constant and stores less heat.

Some pore shapes trap materials, while others allow free flow in and out of the spheres.

The different kinds of sphere porosity may resemble slits between onion-like layers of silica, or a honeycomb's hexagonal patterns of holes, or the cubic gaps in a network of connected tinkertoys.

"The ability to control these different porosities make them useful for all kinds of applications," says Sandia lead investigator Jeff Brinker. "If they were simply porous particles, they would not be nearly so interesting."

The mixture begins with a homogeneous solution of soluble silica plus surfactant prepared in an ethanol water solvent. In a continuous process that takes about six seconds per particle, the aerosol particles are dried,