Electrically Conducting Polymer Composites

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Electrically Conducting Polymer Composites

• Ragy T. Ragheb, Dr. Y. Lina, Dr. J. Rifflea, Dr.
  J. Hoyt-Lallib, Dr. J. Mechamb
• aDepartment of Chemistry, Virginia Tech,
• Blacksburg, VA 24061
• bNanosonic, Inc., 1485 South Main Street,
• Blacksburg, VA 24060

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What is an ECPC?

• Two components
• Polymer matrix
• Networked polysiloxane
• Thermally stable
• Moisture resistant
• Electrically conducting
• Filler
• Silver flakelets
• Very conductive
• Max contact per unit weight

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Background contd.

• Percolation
• Electrical conductivity is characterized by
  dependence on filler volume fraction. As filler
  amount in the composite is increased , the filler
  particles begin to contact each other and a
  continuous path is formed through the volume of
  the sample for electrons to travel.
• Variables detrimental to conductivity
• Adsorption of water (non-conductive medium)
• Air voids

Critical volume
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Research Motivation

• Tailor percent functional groups on matrix to
  efficiently complex with silver flakelets
• Synthesize and measure conductivity of different
  volume fractions of silver to determine critical
  volume
• Observe change in conductivity with degree of
  applied stress about the critical volume

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Poly(dimethyl-co-methylhydrido)siloxane
Prepolymers
Step 1
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Poly(dimethyl-co-methylhydrido-co-cyanopropylmethy
l)siloxane via Hydrosilation
Step 2
Hydrides left for further crosslinking Nitriles
serve as polar functional groups
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Hydrosilation progress monitored by 1H NMR
MW 5740 g/mol
T 0 minutes
Vinyl protons
hydrides
T 30 minutes
MW 6443 g/mol 25.5 CN
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Networked Poly(dimethyl-co-methylhydrido-co-cyanop
ropylmethyl)siloxane via Hydrosilation
Step 3
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Catalyst study monitored by ATR

• This Attenuated Total Reflection (ATR) technique
  used in the mid-infrared region where absorptions
  due to molecular vibrations can be utilized to
  analyze the curing process of solid-state
  samples.
• Monitored the disappearance of the Si-H stretch
  at 2150 cm-1 as compared with standard Si-O
  stretch at 1009 cm-1.
• Percent hydrosilated Si-H as a function of time.

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Compositions Curing Process

• STEP 1 Add Pt catalyst, crosslinking agent, then
  polymer
• Mix and degas
• STEP 2 Add silver particles
• Mix and degas
• STEP 3 Prepare thin films on glass slides for
  conductivity tests (Cured at 80C overnight)

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Stress Applications
Applied Fatigue
Applied Fatigue
Dogbone
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Epoxy resin
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Conclusions

• Successfully synthesized both low and high MW
  poly(dimethyl-co-hydridomethyl)siloxane
  prepolymer.
• Successfully hydrosilated low molecular weight
  (5470 g/mol) prepolymer to yield 25.5 mol CN.
• Hydrosilation of high molecular weight prepolymer
  (40,000-50,000 g/mol) could not be completed
  regardless of temperature, target CN, or
  catalyst concentration. Vinyl groups on
  Karstedts catalyst complex could hypothetically
  cause crosslinking even in mild conditions.
• Epoxy resin proved to be slightly malleable and
  will be used for stress tests. Composite proved
  to be electrically conductive while imbedded in
  the resin dogbone.

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Future Work
Step 1
Step 2
Will hopefully allow for higher molecular weight
networks
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Future Work contd.
Step 3

• Search for a solvent to dissolve oleic acid and
  remove lubricant from silver flakelets to allow
  for better complexation with network.
• Make a series of composites with different
  fractions of silver.
• Test change in conductivity as a function of
  applied stress on dogbone molds.

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Acknowledgements