Iowa State University researchers have found a new way to change the surface structures of liquid metals with the help of heat.
Treating particles of liquid metal alloys with heat causes them to roughen their surfaces with tiny spheres or nanowires. This is reminiscent of how a chameleon changes its skin color in response to its environment.
Controlling the heat allows you to control the surface patterns, notes lead author and Iowa State assistant professor Martin Thuo.
According to Thuo and his team – which includes postdocs Andrew Martin and Winnie Kiarie, and University of California, Berkeley postdoctoral fellow Boyce Chang – the new technology could inspire 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 has been 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.
According to the scientists, the most reactive, gallium, breaks through first. More heat brings indium to the surface, and the highest heat – about 1,600 degrees Fahrenheit – 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,” explains Thuo.
“That’s why we say they’re chameleon metals – but responding to heat, not to color as the reptile does.”
As the metal particles respond to a very controlled environment, this allows the scientists to predict and program the exact surface texture of the particles.
Martin says the new technology could be used to fine-tune a metal’s performance as a catalyst or its ability to absorb compounds. It can also be used with other metal alloys too.
Image and content: Andrew Martin/Iowa State