Charged microdroplets turn minerals into nanoparticles

Microdroplets of water are capable of incredible chemistry; the tiny pools have vastly different properties different from those of bulk water. Now, researchers led by Thalappil Pradeep of the Indian Institute of Technology Madras have observed minerals spontaneously breaking down into nanoparticles when suspended in charged microdroplets (Science 2024, DOI: 10.1126/science.adl3364).

Silicon dioxide, or quartz, was chosen as the first mineral to investigate because of its high natural abundance, Pradeep says. For the experiment, graduate student B. K. Spoorthi ground a sample of river sand into a powder with grains fine enough to be suspended in microdroplets. The team loaded water and the sand into a home-built electrospray setup, which delivered charged microdroplets onto a piece of aluminum a few centimeters away.

Later, transmission electron microscopy revealed the metal was peppered with round silica nanoparticles: the bonds in the quartz had broken down in mere milliseconds. It’s such a violent process that Pradeep thinks of the charged microdroplets as “wet fire.”

“To see what they saw is astounding,” says Michael Hochella, a geoscientist at Pacific Northwest National Laboratory who has studied the role of nanoparticles in nature for nearly 30 years. Despite both quartz and ruby taking millions of years to naturally dissolve, “here they are, breaking down dramatically and easily in very short amounts of time,” Hochella says.

More research will reveal whether similar processes happen in naturally occurring microdroplets—a theory posited by the authors—but Hochella thinks “there’s no question that they have hit on something that is going to be studied for a long time.”