Silica, or silicon dioxide, is the same material used to make glass. In nature, silica makes up quartz and the sand you walk on at the beach. Unlike metals such as gold and iron, silica is a poor conductor of both electrons and heat. Despite these limitations, silica (silicon oxide) nanoparticles form the framework of silica aerogels. Silica aerogels are composed of silica nanoparticles interspersed with nanopores filled with air. As a result, this substance is mostly made up of air. Because air has very low thermal conductivity and silica has low thermal conductivity, they are great materials to use in insulators. These properties make nano aerogels one of the best thermal insulators known to man.
You can also functionalize silica nanoparticles by bonding molecules to a nanoparticle that also is able to bond to another surface, such as a cotton fiber. The functionalized silica nanoparticles attach to the cotton fiber and form a rough surface that is hydrophobic (water repellent), giving an effect similar to the water repellency of lotus leaves.
Another type of silica nanoparticle is riddled with nanoscale pores. Researchers are developing drug delivery methods where therapeutic molecules stored inside the pores are slowly released in a diseased region of the body, such as near a cancer tumor.
Silicon dioxide nanofilms, a layer of silicon dioxide molecules that can be as thin as 1 nm, are used to provide electrical insulation between two parts of a device, such as a transistor. This method is used in making computer chips.
Excerpted from Nanotechnology For Dummies (2nd edition), from Wiley Publishing