China’s Zhejiang University has developed a new liquid metal, alginate ink that can be used for 3D printing intricate, flexible and durable circuits onto smart clothing.
Alginate is a polymer derived from algae; once coated on 3D printable liquid metal droplets, these enable the printing of cost-effective circuits onto a variety of fabrics that are stable enough to withstand the twisting and stretching motions that clothing typically undergo during daily activities.
Of late, gallium-based liquid metals (LMs) are turning out to be the preferred choice of material for flexible electronics thanks to their fluid nature and excellent conductivity.
However the one drawback holding them back from being widely used in smart clothing is that LMs don’t stick well to fabrics, and their large surface tension causes them to ball up during 3D printing.
Zhejiang’s Yong He and colleagues have now showcased their new liquid metal-alginate conductive ink that can be 3D printed directly onto clothing in complex patterns.
In order to make their ink, He and his teammates mixed LM and alginate. They kept stirring the solution and removed the excess liquid resulting in LM microdroplets coated with an alginate microgel shell.
According to the scientists, the ink was at first very thick until it was squeezed through a nozzle for 3D printing, which broke hydrogen bonds in the microgel and made it more fluid.
Once the ink reached the fabric surface, the hydrogen bonds reformed, causing the printed pattern to maintain its shape.
In order to show the ink’s versality, He and his teammates 3D printed the same onto a variety of surfaces, including paper, polyester fabrics, nonwoven fabrics and acrylic-based tape.
It should be noted that the printed patterns were not initially conductive, but the scientists managed to activate them by stretching, pressing or freezing, which ruptured the dried alginate networks to connect the LM microdroplets.
After activation, the printed circuits had excellent electrical conductivity and strain sensing properties. In addition, applying a small voltage to the ends of the circuit caused it to heat up, even in very cold temperatures.
According to the scientists, the best feature of this new LM-alginate ink is that it can be recycled by soaking the fabric in a weak sodium hydroxide solution. This enables recovery of the fresh liquid metal for new applications.
Image and content: American Chemical Society (ACS)
