To make the ink, the team produced silver nanoparticles by reducing a silver nitrate solution along with an acid to prevent the particles from growing too large. Afterwards the acid was removed and the viscosity of the ink modified using hydroxyethyl cellulose to get just the right consistency. The result is a sort of liquid metal that dries on contact and which can be used to conduct electricity, hence its ability to be used in the creation of a circuit.
|University of Illinois engineers developed a pen with|
conductive silver ink that can write electric circuits and
interconnects directly on paper and other surfaces.
Credit: Bok Yeop Ahn
Up till now, most research on printing circuits onto non-standard materials, such as paper, have been done using inkjet printers or even airbrushes. This new approach would allow circuits to be drawn quicker and much cheaper, or even on-the-fly, as no other hardware is needed. Such a low cost device might create a market for throwaway circuits or even super cheap batteries. Paper was used in the study because it is considered to be the most suitable non-standard material for printing circuits due to its wide availability, low cost, ability to be bent and shaped, and the fact that it is biodegradable.
Lewis noted that the paper used in study was folded after testing to see how the circuit would hold up, and discovered it took folding several thousand times before the ink pathways were broken. She also noted that other materials besides paper could be used, such as wood or ceramics.
|This is a flexible array of LEDs mounted on paper.|
Hand-drawn silver ink lines form the interconnects
between the LEDs. Credit: Bok Yeop Ahn
The team next plans to look into other types of materials that might be used to make conductive ink for their pen, hoping to open up the door to all kinds of inks that can be used for a wide variety of purposes.
More information: Pen-on-Paper Flexible Electronics, Advanced Materials, Article first published online: 20 JUN 2011. DOI:10.1002/adma.201101328