0. Preparation of Solid Silver Nanoparticles for Inkjet Printed Flexible Electronics with High Conductivity
Paper Written By
Wenfeng Shen, Xianpeng Zhang, Qijin Huang, Qingsong Xu, Weijie Song
Presented By
Gabe Shindnes, Liza Ross, Bill Shi

1. Purpose Utilize Ag nanoparticles to develop a method to print
flexible electrical circuits.
Flexible printed LED array

2. Inkjet Printing Applications
Inkjet printing technology has been used for LED’s, photovoltaic cells, and sensors.
Smart Clothing

3. Remaining solution: Nanoparticles
Possible Conductors
Conductive Polymers, Graphene, Carbon
Organo-metallic compounds
Metal precursors
Metal nanoparticles
Why they are not suitable for application:
Polymers, graphene and carbon have too low conductivity
Organo-metallic compounds and metal precursors require too high temperatures
Remaining solution: Nanoparticles

4. TEM Image of Ag Nanoparticles
Silver Nanoparticles
Chosen for their good conductivity, low resistivity, reasonable cost and resistance to oxidation.
TEM Image of Ag Nanoparticles

5. Synthesis of Poly(acrylic acid) (PAA)-coated AgNP
Silver source: silver nitrate (AgNO3)
Reducing agent: Monoethanolamine (MEA)
Capping molecule: Poly(acrylic acid)
Medium: deionized water
AgNO3 --->PAA coated, charged nanoparticles
dispersed in aqueous solution
1. Undergo vigorous magnetic stirring for an hour
2. Heated up to 65 degrees Celsius
3. Colors vary in the sequence of yellowish, brown, orange, and dark red.
4. A black precipitate of PAA coated AgNP is collected after adding ethanol
5. Collected through funnel and washed with ethanol to remove residual MEA and PAA

6. Inkjet Printing and Heat Treatment of Silver Patterns
Silver ink lines were printed using a common color printer
AgNP inks printed on Kodak photo paper, and polyethylene terephthalate (PET)
PET substrate was precoated with Poly(diallyldimethylammonium) chloride (PDAC) so the ink would sinter at room temperature
Kodak paper already had PDAC-like molecules
After printing, samples are heat-treated at temperatures ranging from ℃.
Then:
The structural and electric properties of silver patterns are investigated

7. Dependent Variables and Measurement Methods:
Structural characterizations (electron density, atom positions) - X ray diffraction
Particle size distribution and morphology- Transmission electron microscope
Viscosity of AgNP- Viscometer
Surface tension- Drop weight method
Electrical resistivity- 4 point probe system

8. Results and Discussion
Properties of Poly Acrylic Acid
The powder obtained from grinding solid silver NPs was observed with an X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM- results not shown with SEM), Thermogravimetric/Differential Thermal Analysis (TG/DTA)
XRD: results demonstrate that the powder was composed of well-crystallized silver NPs, and that the PAA-coated silver particles did not change after being held in the room for 3 months
Scherrer Formula ( ; formula that determines the size of particles in the form of powder)
Showed that all particles were approximately 30nm
Poly Acrylic Acid

9. Results and Discussion
TG/DTA: data showed a miniscule weight loss from room temperature to 300℃ of 0.7%
caused by the release of organic molecules from the surface of the silver NPs
0.1% weight loss from 955℃ to 1000 ℃; caused by temperature disturbance
99.2 % of weight was pure silver
Benefit of using silver NPs is that they can be stored at room temperature
can also be prepared as printing material by dispersing NPs with water
Silver NPs ranged from 20nm to 230nm, with mean being somewhere between 30 to 50 nm

10. Results and Discussion
TEM (Transmission Electron Microscope) Data
Data obtained from TEM on Silver NPs:
Particle size ranged from nm
The majority of the particles were less than 40nm
Data agrees with the data obtained from the X-Ray Diffraction (XRD) analysis
Transmission Electron Microscope

11. Results and Discussion
Silver NP Ink Properties
Purpose: Produce small liquid silver droplets and to deposit them in a specific location on a substrate
Most important properties of droplets for this : Viscosity and Surface Tension
Increasing the density of Silver NPs in the liquid showed a positive correlation in both Viscosity and Surface Tension
Other important properties to consider when working with non- Newtonian fluids:
Jet Velocity, Characteristic radius (radius of the orifice), and Density
Dimensionless numbers that describe these properties
Reynolds, Weber (measures spreading behavior)

12. Results and Discussion
Properties of Silver NPs
The Ohnesorge number describes the physical properties of the ink and the size of the scale
Oh ranges from 0.1 to 1.0 since Z ranges from 1 to 10
A high Z (larger than 10) will create a large number of viscous satellite droplets
A low Z (smaller than 1) will prevent the separation of the droplets due to the viscous forces
The Z value of the silver droplets that were created (varying in weight from 10 to 25 percent) ranged from 9.94 to 7.00 which made these inks printable

13. Results and Discussion
The printed line width was set at 1pt, equating to approximately 530μm.
If the silver nanoparticles were heated at higher temperatures, the more conductive the lines became
At higher temperature, there were less cracks, helping induce electrical conductivity
Lines were printed 14 times, with each print decreasing the resistance at an exponential rate
a) Room Temperature b) 50oC c) 80oC d) 140oC

14. Results and Discussion
Greatest resistivity difference between temperatures with only one print cycle, but decreases significantly with additional print cycles
8μΩ cm when sintered at room temperature compared to 3.7μΩ cm at 180oC
Allows high conductivity at low temperatures
This is important because it allows for inkjet printing for paper and plastic products

15. Conclusion:
Synthesis of PAA coated AgNPs kept at room temp. without degeneration
Low cost reaction and environmentally friendly
No centrifugation—Ideal for low cost and mass production
Lowest electrical resistivity measured
was 8.0 µΩ cm → high conductivity