Image credit : New Scientist
Paper isn’t exactly a smart material, but if it were coated with a novel liquid metal, one day it might be. Paper and other materials could be transformed into tools that can do some tasks on their own using this liquid alloy.
Although not as a coating, liquid metal is already employed in smart items like circuitry and wearable sensors. Scientists at Tsinghua University in China, under the direction of Bo Yuan, have developed a method to create liquid metal and apply it with a stamp such that it adheres to paper without adhesive, which has never been done before. The method was inspired by the art of origami.
In a study that was just published in Cell Reports Physical Science, the researchers demonstrated how metal-coated paper can be folded into origami designs and then refolded. Additionally conducting heat and electricity is the metal covering. It resembles magic. Almost.
It is challenging to get liquid metal to stick to any surface without any glue since the particles in it have a tendency to stick together tightly. But the qualities of the metal, such conductivity, are typically adversely affected by these adhesives. Yuan and his team sought a liquid metal with adhesive-free adhesion to paper. They compared the performance of an indium/gallium alloy (eGaIn) to an alloy made of bismuth, indium, and tin oxide (BiInSn).
BiInSn proved to be more successful. It does not oxidize when exposed to air, in contrast to eGaIn, therefore the oxide coating that develops on the metal has no bearing on how well it adheres to a surface.
Since BiInSn has a greater melting point and is a solid at room temperature, there is no danger of it liquefying at temperatures below 62° Celsius (about 144° Fahrenheit). Additionally, it has stronger adhesive abilities. However, it took some trial and error to get the best adhesion out of BiInSn.
“We needed to ensure the adhesion of liquid metal to be uniform in large scale on different paper, and to maintain the stability of the coating,” Yuan told Ars Technica in an email interview. “To solve these problems, we changed pressure applied on the stamp as well as the rubbing speed used in the experiments and finally found the most suitable parameters, which finally achieved fast, large-scale, and stable adhesion.