Unbearable Lightness of Gold
“Featherweight” gold floats on coffee foam…
Just think: You will not have to suffer the embarrassment of giving the bride only a quarter of the customary gold coin at your best friend’s wedding. You could present her a big gold chalet instead – at, an even smaller cost. You can craft it yourself, if you want. Or you can improve your social standing by placing a gold coin on their cappuccinos at the gathering of the “girls.” And anyone hoping to stick a pin to your inflating status by scraping the coating will be disappointed. It’s real, 20-carat gold! Well, do not hasten to send the invitation cards: allow the technology developed by Swiss researchers to take hold.
What the researchers at ETH Zurich (Swiss Federal Institute of Technology) have developed is a form of gold which is light enough to float on cappuccino foam.
Developed by a team led by Food and Soft Materials Professor Rafaele Mezzenga, the structure in the form of aerogel weighs one-thousandths of the mass of a gold alloy of the same volume. With a density less than that of water, the gold is almost as light as air.
The gold in aerogel form is indistinguishable from normal gold and has the same metallic shine. The only difference is its softness and malleability. For gold aerogel is 98 pars air and 2 parts solid material. And of this solid part, more than four-fifths is gold and less a fifth is made of milk proteins, making the structure equivalent to 20 carat gold.
To make the material, researchers first heated milk proteins to produce protein fibers of nanometer size called amyloid fibrils, which they then dipped into a solution of gold salts. As the protein fibers began to form three dimensional structures, the gold in the solution crystallized around these scaffolds as tiny particles. In the end, a web of gold filaments emerged in the consistency of jell-o.
By manipulating the reaction conditions, the gold can be given lighter or darker color and values of absorption and reflectance can be altered, the researchers explain.
Mezzenga notes that the lightness of the material, the less metal it requires and its spongy structure makes it advantageous for several applications where ordinary gold is used, such as jewelry and watchmaking. And its porous structure, providing a huge surface area, makes the material an ideal catalyser to speed up chemical reactions, the researchers stress.
The featherweight gold material can also be used in the manufacture of pressure sensors. Since the gold particles in the material do not touch each other under normal conditions, the gold aerogel does not conduct electricity. But when pressure is increased, the material contracts and particles begin to touch, making the aerogel conductive.
- 1. “A new form of real gold, almost as light as air”, ETH Zurich, 25 November 2015