Bulk PALS Measurements of P2VPSilica Nanocomposites

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Bulk PALS Measurements of P2VP/Silica
Nanocomposites
David Welch Rhodes College
Mentors David W. Gidley Richard
Vallery University of Michigan Physics Department
Research Experiences for Undergraduates Summer
2007
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Outline

• What is antimatter (positron)?
• What happens to antimatter in the presence of
  matter?
• What can we do with antimatter?
• What is a polymer nanocomposite (pnc)?

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The anti-electron, or positron

• All particles have anti-particles of equal mass
  but opposite charge
• Anti-electron is the positronnatures lightest
  and simplest antiparticle
• Positrons annihilate electrons with
• 100 energy conversion, Emc2

e- e
Is there a more physical picture of annihilation?
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What is the Fate of a Positron?
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The Simplest Atom
While annihilation is the inevitable fate of a
positron (at least in the presence of matter) a
lot can happen on the way
It can bind with an electron and form Positronium!

• Positronium (Ps) shares many of the features of
  Hydrogen
• Electrically neutral
• It has a binding energy of ½ Rydberg (6.8 eV)
• It has energy levels
• It has two spin states Spin singlet
  (para-positronium) 0.12 ns
• Spin triplet (ortho-positronium) 142 ns

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Positrons in Material Science

• Is it crazy to use antimatter in materials
  science?
• Some other probes
• Photons IR, visible, UV, x- and gamma- rays
• Electrons secondary, diffracted, tunneled
• Neutrons
• He nuclei
• Sputtered atoms..

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Guiding Principle
Use antimatter to probe the electronic
environment near the point of annihilation
Ps and e tend to trap in vacancies and voids
Candidate targets are any bulk or thin film
materials where vacancies, voids, pores affect
mechanical, electronic, and transport properties
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The Positronium Lifetime, t
R
Ro
Ro
R
Electron Cloud

• Quantum Mechanical Model measure wave function
  overlap with electron cloud
• Tau-Eldrup Direct correlation between lifetime
  and pore size

• Measured t shortened by wall collisions
• Frequency of collisions dependent on pore radius
• Correlate pore size, R, and t

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Positron(ium) Annihilation Lifetime Spectroscopy
Heater Box
Start Detector
Stop Detector
Positron Source
Sample

• Bulk PALS (mm)
• Well known probe of subnanometer voids in
  polymers
• Straight-forward experimental setup
• Only applicable to homogeneous bulk samples

David Welch Captain of the bulk PALS
battleship Ross Smith Commander of PALS
analysis of P2VP and Struick Specialist
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Lifetime Spectrum
Annihilations from positrons
Annihilations from orthopositronium
Characteristic orthopositronium lifetime, t,
shortened by quenching
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Polymer Nanocomposite

• Reinforcement of polymers by means of fillers
• Alter thermal mechanical properties
• Enhance performance of the polymer
• Our Sample
• 14 nm diameter silica dispersed in P2VP
• Different loadings of silica

P2VP/MEK/silica
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P2VP Temperature Scans
Rubber Expansion
Glass Transition (Tg)
Glass Expansion
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P2VP Temperature Scans
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P2VP Quench Cool
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Struick Model
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Conclusions

• Quench Cool
• Very dynamic system
• Struick Aging Model
• Surface chemistry or thermodynamics in a
  frustrated system
• Temperature Scans
• Increasing wt, slight increase in Tg
• 20 and above, strong effect on glass phase
  expansion
• 60, strong effect on rubber phase expansion
• 5 anomalous

Image courtesy of Harton and Kumar, Columbia
University
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Future Work

• Temperature Scans
• Run a new sample of 5
• Run a 10, 50 sample
• Decrease error bars
• Samples with
• Different size silica
• Different MW P2VP
• Quench Cool
• Age 60 at 80 and 110ºC
• Reproduce data

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Acknowledgements
A special thanks to my mentors David Gidley and
Richard Vallery Our collaborators at Columbia
Sanat Kumar and Shane Harton And fellow
undergraduate researcher Ross Smith Also the
University of Michigan Physics Department and NSF
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Questions?
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But where do positrons come from?
Certain radioactive materials naturally emit
positrons 22Na, 58Co, 64Cu, 68Ge, amongst many
However, Emc2 works both ways ? convert energy
into mass!
Pair Production
Atom

• These high-energy g-rays are present in
• Cosmic rays
• Particle Accelerators
• Lasers
• Nuclear Reactors