Just like a chameleon changes its skin color in response to its environment, engineers have found a way for liquid metal — and potentially solid metal — to change its surface structure in response to heat. Treating particles of liquid metal alloys with heat causes them to roughen their surfaces with tiny spheres or nanowires.
The technology could enable design of smart alloy systems that evolve the surface patterns and their composition with temperature (or analogous stimuli) for applications ranging from sensing to catalysis.
The research team started with a liquid metal alloy of gallium, indium, and tin synthesized into particles covered with a smooth oxide shell that was chemically stabilized. As the particles are heated, the surface thickens and stiffens, and begins to behave more like a solid.
Eventually, the surface breaks, allowing the liquid metal inside to come to the surface. The most reactive — gallium — breaks through first. More heat brings indium to the surface. And the highest heat — about 1,600 °F — brings out florets of tin.
This movement from the under-layer to the surface allows a liquid metal particle to continuously invert its composition under thermal stimuli. The particles are responding to a certain level of heat and releasing a specific element based on temperature, just as a chameleon responds to the color of its environment, but the particles respond to heat, not to color as the reptile does.
The metal particles respond to a very controlled environment — time, temperature, and oxygen levels are carefully controlled by the researchers. That allows them to predict and program the exact surface texture of the particles. The technology could be used to fine-tune a metal’s performance as a catalyst or its ability to absorb compounds.
The technology will work with other metal alloys since it is a behavior of metals in general. Other metals subject to the same treatment should do the same.