Now that’s a gem of a process

Chemists say they have caused common microparticles to spontaneously organise into highly ordered crystalline materials – the equivalent of table salt or opals – using just electrostatic charge. 

And that’s more exciting than it may sound to non-chemists, they suggest, because it shines a light on self-assembly processes that could be used to manufacture new functional materials.

Stefano Sacanna and colleagues from New York University present their findings in the journal Nature.

One approach to programming particles to assemble in a particular manner is to coat them with DNA strands; the genetic code instructs the particles on how and where to bind with one another. 

However, the researchers say, because this approach requires a considerable amount of DNA, it can be expensive and is limited to making very small samples.

In their study, they used electrostatic charge rather than DNA, in a process not dissimilar to what happens when you mix salt into a pot of water. When salt is added to water, the crystals dissolve into negatively charged chlorine ions and positively charged sodium ions. When the water evaporates, these recombine into salt crystals.

“Instead of using atomic ions like those in salt, we used colloidal particles, which are thousands of times bigger,” says Scanna. “When we mix the colloidal particles together under the right conditions, they behave like atomic ions and self-assemble into crystals.” 

The researchers also used self-assembly to create colloidal materials that mimic gemstones, particularly opals.