Scientists at the Swiss Federal Institute of Technology in Zurich have created a gold aerogel: a porous material that is 98 per cent air. The rest is mostly gold, except where it’s milk. Yes, milk. To make the gel, milk proteins were heated up just enough to form ultra-fine fibres. This has been done before, but in the past, the network of fibres was set up first and then coated with gold. The result was an inconsistent mess, where certain parts of the gel were covered in gold and others were bare.
This time around, the milk protein fibres were covered in gold salts while the network was still being formed. The gold crystallised onto the fibres while they were coming together to form the internal structure of the gel. The result is a pillow that’s gold through-and-through.
It doesn’t always have to look so pretty. This image shows the plain aerogel, then the camera-ready one covered in gold microparticles. The last version is covered in gold nanoparticles, which turns the gel a dull maroon.
Scientifically, the fact that the appearance changes so much makes it more valuable. Because absorption and reflection of photons changes depending on the size of the particles, scientists using aerogel have a variety of options.
Researchers are still considering how to use the material. It’s a great way to cover a large area with a very small amount of gold, which might help scientists who need to scale up their experiments. Also, while gold aerogel does not conduct electricity because the particles of gold don’t touch each other, you can change that property by squishing it a little so that they do. So it could be used as an extremely delicate pressure sensor. [Paper: Amyloid Templated Gold Aerogels]
Feather, Flower, and Cappuccino Images: Gustav Nyström and Raffaele Mezzenga / ETH Zurich. Gold Disc Comparison Images: Nyström G et al. Advanced Materials 2015.