But perhaps we should think more in terms of two of those Greek “elements”: air and water. Many vital materials for hi-tech industry are in short supply but air and water are massively abundant. Wouldn’t it be wonderful if we could make mouldable solid materials from these primal (but not elemental) substances?
An obvious pipedream but thanks to nanotechnology it is coming true. It has been known for along time that the paradoxical way to make strong material is to leave much of the solid stuff out. The honeycomb core of composite panels is strong and exceptionally light. What this idea tends towards is the solid foam and this was realised a long time ago in the form of aerogels.
The aerogel was invented as long ago as 1929. It is a foam from which the water has been withdrawn, leaving the structure intact and replacing the water with air. The most common material is silica, which is also used by nature in the intricate Buckminster Fuller-like structures of the tiny marine radiolarians. Aerogels have been much developed since their invention but they are still fabulously expensive, Their main applications have been in space technology.
What is special about them? Aerogels are the lowest density materials known. They are so wispy that the name “solid smoke” has been coined for them. They are almost transparent but not quite, having an eerie bluish cast They are tough in compression but above all they are the most efficient insulators on earth. A crayon placed on aerogel cannot be melted by a Bunsen burner placed underneath. If aerogels could be made more cheaply they would revolutionise insulation technology, especially in the home.
Various figures are quoted for the proportion of air in an aerogel, but it is reliably over 90%; the highest figure I’ve seen is 99.8%.
Can the same be done with water? Yes: a Japanese team has developed mouldable plastics consisting of 98% water. The secret of both the air and water substances is dendritic molecules. These are large many branched molecules in which the endless ramifications provide a strong network which encloses the air or water. The idea seems entirely counter-intuitive, like most nanotechnology, but both aerogels and aqua plastic pass the Dr Johnson test of reality: they are solid – you can stub your toe on them. And so much more.
With thanks to Dan O’Dwyer for reminding me about the properties of aerogels.
Q. Wang, et al. High–Water–Content Mouldable Hydrogels by Mixing Clay and Dendritic Molecular Binder, Nature 2010, 463, 339.