Martin Thuo, an assistant professor of materials science and engineering at Iowa State University, and his research group are using materials expertise to study soft matter, single-molecule electronics. One of the team’s latest innovations is finding a way to make micro-scale, liquid-metal particles that can be used for heat-free soldering plus the fabricating, repairing, and processing of metal—all at room temperature. The liquid metal particles could have significant implications for manufacturing.

The project began as a search for a method to stop liquid metal from returning to a solid, even below the metal’s melting point. That is called undercooling. But, the team revealed, it has been a challenge to produce large and stable quantities of undercooled metals.

However, the team suspected that if tiny droplets of liquid metal could be covered with a thin, uniform coating, they could form stable particles of undercooled liquid metal. They experimented with a new technique using a high-speed rotary tool to sheer liquid metal into droplets within an acidic liquid. The particles are exposed to oxygen and an oxidation layer is allowed to cover the particles, creating a capsule containing the liquid metal. That layer is then polished until it is thin and smooth.

The researchers were able to prove their concept by creating liquid-metal particles containing an alloy of bismuth, indium, and tin and particles containing an alloy of bismuth and tin. The particles are 10 micrometers in diameter, about the size of a red blood cell.

“We demonstrated healing of damaged surfaces and soldering/joining of metals at room temperature without requiring high-tech instrumentation, complex material preparation, or a high-temperature process,” the engineers stated.