Paper is a product that we can use for many purposes such as writing, printing, packaging and handicrafts. What if paper could do more than just hold ink or fold it into shape? What if paper could transform itself into smart objects that could sense, act, and communicate? This may sound like science fiction, but a group of researchers from China recently developed a new method by coating paper with liquid metal, giving it unprecedented abilities.
Liquid metal, a type of metal that remains liquid at room temperature or slightly above; It has many features such as high conductivity, low fluidity and self-healing. liquid metal; Circuits can be used to create flexible and stretchable electronics such as sensors and actuators.
However, applying liquid metal to paper or other substrates is a bit tricky because liquid metal tends to form droplets and doesn’t stick well without an adhesive, so scientists have found a way to bypass this.
Researchers led by Bo Yuan of Tsinghua University have found a solution to this problem by using a special alloy made of bismuth, indium and tin oxide (BiInSn). This alloy has a higher melting point than other liquid metals such as gallium or eutectic gallium-indium (EGaIn), meaning it can be solidified and stamped on paper without dripping or spreading. The alloy also does not oxidize when exposed to air, making it more stable and sticky.
To coat the paper with BiInSn, the researchers first melted the alloy in a crucible and poured it into a silicon mold. They then pressed the mold onto a piece of paper at moderate pressure and speed. The result was a thin and uniform layer of liquid metal on the paper surface. The researchers repeated this process on both sides of the paper to create a double-sided coating.
The coated paper showed remarkable properties. It could conduct electricity and heat, which allowed it to illuminate LEDs and resistors. It could also sense touch, pressure, and temperature changes. Moreover, it could fold itself into different shapes by applying an external magnetic field. The researchers demonstrated this by making an origami cube from coated paper. When they opened the cube and placed it next to a magnet, the paper itself folded back to its original shape.
Are smart papers entering our lives?
The researchers believe their method could open up new possibilities for creating smart paper devices that can perform a variety of functions. For example, they envision paper-based robots that can move and interact with their environment, paper-based displays that can change colors and patterns, and paper-based sensors that can monitor health and environmental conditions.
The method is also simple and scalable, meaning it can be applied to large-scale production of smart paper products. The researchers claim that their method can coat any type of paper with liquid metal, regardless of thickness, texture, or color. They also suggest that other materials other than paper could be coated with liquid metal using the same technique.
(You can find the research published in Cell Reports Physical Science on June 22, 2023 here.)
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