a new liquid-metal ink. Conductive inks made from silver nanoparticles have been available for some time; recently, a group at Georgia Tech demonstrated a way to use them in inkjet printers to create custom circuits. But they are quite pricey, and I’m not keen on the idea of pumping metal through my printer. In contrast, this new ink can be used in an ordinary roller-ball pen to draw circuit traces, and the recipe for making the ink is amazingly straightforward: Mix 75.5 parts gallium with 24.5 parts indium in a beaker of deionized water, heat to 50 °C, stir, and voilá: an alloy that’s liquid at room temperature, costs about US $1 per milliliter, and is two orders of magnitude more conductive than the nanoparticle inks; its resistivity is just 17 times that of copper.
I phoned the senior author on the paper, professor Jing Liu of the Technical Institute of Physics and Chemistry at the Chinese Academy of Science, in Beijing, to check that this was really something I could do at home. Use 99.9 percent pure gallium and indium, he advised; I bought the metals from GalliumSource.com for about $130. The pen cartridge needs to be completely clean before filling, and the liquid alloy must be free of any solid bits that might clog the tip. Most important, write on plastic transparencies. The surface tension of the ink is so high that it beads up on paper.
So cool, I have to try this!