This isn’t a dirty, peeling sticker but a scientific first. Researchers have been able to make complex 2D and 3D structures using nanoparticles for years — but they have never before been able to curve or fold a flat sheet of them like this.
Now, researchers from the University of Chicago, the University of Missouri and the US Department of Energy’s Argonne National Laboratory have developed a way to do it. These images show a series of membranes of gold nanoparticles coated with organic molecules, that have curled up into tubes after being hit by an electron beam.
The reason is to do with the way the sheets are made. Gold nanoparticles are connected by a series of oil-like organic molecules, forming sheets when they’re floated on top of water. The water is then evaporated away, leaving small sticker-like patches over holes in a frame below. They’re a little like drum skins.
But the organic molecules that hold the gold nanoparticles together are hydrophobic, so they’re not evenly distributed top-to-bottom across the sheet when the water evaporates. When an electron beam hits the surface, it causes the molecules to create a new bond with their nearest neighbours, but because of their distribution more occur on one side than the other. In turn, there’s an unsymmetrical stress in the sheet that causes it to curl or fold.
At the moment, the scientists can’t tune the distribution of organic molecules in the sheets, so they have no control over the curling. But they’re now embarking on a series of experiment to work out how they could control the folding, in order that they could induce the effect in pretty much any nanoparticle membrane hey choose.