illustrated by James burke
Mix up a homemade batch using some basic chemistry skills
WRITTEN AND PHOTOGRAPHED BY JORDAN BUNKER
THANKS TO RECENT SCIENTIFIC ADVANCES, YOU CAN BUY CONDUCTIVE INKS IN THE FORM OF PENS, PAINTS, AND EVEN PRINTER CARTRIDGES, but have you ever wondered if you could make your own?
You can, and following a simple process developed by the University of Illinois Urbana-Champaign Materials Research Laboratory, it’s actually quite easy to produce the conductive ink at home.
The following steps have been adapted from the UIUC paper titled “Reactive Silver Inks for Patterning High-Conductivity Features at Mild Temperatures,” and have been simplified for the amateur chemist.
Clean all glassware and tools and lay them out on your work surface. It is important to read through all of the steps, and make sure that you understand them thoroughly before beginning.
Rather than using an expensive laboratory vortex mixer, you can make your own using a 2" bolt and a circular piece of wood.
Cut a circle approximately 2½" in diameter from a piece of ½" thick wood. Drill a centered hole large enough to fit the shaft of the 2" bolt. Drill a second ½" hole halfway into the wood, slightly off-center and overlapping the centered hole (Figure A).
Place the 2" bolt in a bench vise, and then use a hacksaw to remove the bolt head. Insert the bolt shaft into the center hole until it is flush with the bottom of the ½" hole, and then secure it with hot glue.
Pour roughly 3mL of ammonium hydroxide into a glass beaker. Using a dispensing syringe, draw exactly 2.5mL out of the beaker and deposit it into the test tube (Figure B).
Place the weight boat on a digital scale and tare the scale. Measure out exactly 1g of silver acetate powder (Figure C) and pour it into the test tube.
Insert the bolt of your homemade vortex mixer into the electric drill. Holding the top of the test tube firmly, place the base of the test tube against the hole in the vortex mixer (Figure D). Slowly increase the speed of the drill until a vortex appears in the test tube, mix for 15 seconds, then set the test tube aside.
CAUTION: The chemicals used are strong-smelling, corrosive, and can stain skin and clothes. You must wear chemical-splash safety goggles, neoprene gloves, a long-sleeve shirt, pants, and close-toed shoes. Due to the fumes created, this project must be done outside or in a fume hood.
Pour approximately 0.5mL of formic acid into a second glass beaker. Using a new dispensing syringe, draw exactly 0.2mL of formic acid out of the beaker (Figure E).
Drip one drop of formic acid into the mixed solution in the test tube (Figure F), then vortex-mix using the same method from step 2. Repeat this process until all 0.2mL of formic acid has been mixed. After mixing, the solution will be a gray or black color. Place a stopper in the top of the test tube, and set the test tube aside to react for at least 12 hours (Figure G).
After 12 hours, the solution should look clear with gray sediment of silver particles in the bottom (Figure H). In order to use the ink in an inkjet printer or airbrush, these particles must be filtered out to avoid clogging.
Remove the plunger from a new dispensing syringe, and place a 0.2μm syringe filter onto the syringe tip. Fill the syringe with the prefiltered solution, and replace the syringe plunger (Figure I).
Pressing slowly but firmly on the plunger, force the solution through the filter and into a small glass vial for storage (Figure J).
Before using the ink, it’s important to choose a suitable material to deposit it onto. In order to boost the conductivity of the ink, it must be heated to 90°C (192°F), so any material you choose must be able to withstand at least that much heat. Using this ink on porous materials such as paper or fabric will not result in a conductive coating, so it is recommended that the material have a smooth surface.
Using a paintbrush, apply the ink to your material of choice; a stencil can be used to create complex patterns. Allow the ink to dry until it turns to a dull gray color.
Heat the material to 90°C (192°F) for at least 15 minutes. You can use a toaster oven or hot plate as a heat source.
The ink is quite fragile and will easily scratch off most materials. To increase adherence, scuff the target surface before ink application. Once the ink is dry, apply clear nail polish to protect the traces.
Unfortunately, you can’t solder onto the dry ink, as molten solder will leach the silver coating away. If you have a Circuit-Writer silver-based ink pen, you can use it to create pads on the traces, which can then be carefully soldered to.
For complete step-by-step instructions and photos see makezine.com/projects/diy-conductive-ink.
CAUTION: Heating in a toaster oven will make the oven unsafe for food preparation.