Printable Electronics Reference Devices and Materials
The teflon wick design for the Micron pen:
Previously, we demonstrated that sub-micron silver ink could be printed into circuits and active devices with a modified Micron pen. After printing, the ink particles were sintered on a hot plate to increase the conductivity.
The process worked well, but the ink was not readily available. Here is a possible method to fabricate the metallic ink. This would allow a cold process metal printing of circuits, devices and 3D structures.
Ionic Salt Crystals: A metal and an acid can form an ionic salt that is water soluble. The metal can be arranged in solution. Then the salt can be reduced back into the metal with a reducing agent. This might be a general way to deliver a range of metals via a water solution. Or the particles can be reduced in the solution to yield a bunch of small particles. The colloid of particles would then be put in the pen.
Silver + Nitric Acid => Silver Nitrate(stains skin) + water + Nitrogen Oxide(a toxic gas) 3 Ag + 4 HNO3 → 3 AgNO3 + 2 H2O + NO
A solution of small silver particles can then be made by mixing the Silver Nitrate with a reducer such as Ascorbic Acid or Sodium Citrate. This transfers an electron back to the silver ion.
Silver Nitrate + Ascorbic Acid = Silver + DHA + Nitric Acid 2AgNO3 + C6H8O6 = 2Ag + C6H6O6 + 2HNO3.
To prevent the small particles from clumping or redisolving, a stabilizer or “capping agent” is added such as Polyacrylic Acid (PAA). PAA + Diethanolamine(DEA) or polyvinylpyrrolidinone (PVP) or Sometimes a dispersing surfactant is used instead.
PAA is the absorbent powder in diapers and is listed as an irritant.
This solution is then heated mildly on a hot plate from 1hr to 24hrs .
- I guess this is mainly for brownian motion.
Next, Ethanol(grain alcohol) which is less polar than water can be added to the water solution which will allow the particles to attract each other and precipitate out.
The particles can be further concentrated by spinning them.
Viscosity: Viscosity increases with the concentration of particles. Solutions of 50% silver particles with a small amount of a viscosity additive were reported to have a viscosity of 0.1-1.0cP. Previously successful inkjet inks had a listed viscosity of 12 cP. Normal drawing inks are near the viscosity of water 0.894 cP.
So target concentrations of 50% silver particles by weight should work.
Notables: Ink-jet fabrication of electronic components S M Bidoki, D M Lewis, M Clark, A Vakorov, P A Millner and D McGorman
NerdRage: Making Silver Nitrate
Pen-on-Paper Flexible Electronics Analisa Russo, Bok Yeop Ahn, Jacob J. Adams, Eric B. Duoss, Jennifer T. Bernhard, and Jennifer A. Lewis
Wikipedia Ethanol precipitation
Preparation and the mechanisms of formation of silver particles of different morphologies in homogeneous solutions, Lorenza Suber, Ivan Sondi, Egon Matijevic, Dan V. Goia
Surface Mount Motherboard Design: