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. 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, heated and collected. As liquid starts to evaporate, the rest of the material self-assembles into a completely ordered particle that, when heated, maintains its shape.