By Jesse L. Gray, III Mentors: Dr. Kimani A. Stancil Dr. James S. Hammonds
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Transcript of By Jesse L. Gray, III Mentors: Dr. Kimani A. Stancil Dr. James S. Hammonds
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EXPLORING THERMAL TRANSFER VIA SURFACE PHONON-POLARITONS IN TUNABLE SILICON CARBIDE BULK
COMPOSITESBy
Jesse L. Gray, III
Mentors:Dr. Kimani A. Stancil
Dr. James S. Hammonds
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Overview Goal and Importance What are Surface Phonon-Polaritons? Making of Nanocomposite Analysis Preliminary Results Discussion Next Steps
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Goal – To make tunable bulk nanocomposite comprised of Silicon Carbide & Polyethylene that exhibits Surface Phonon-Polariton coupling.
Importance – The results will be used to give the capability to tune and dictate the thermal conductance of a material based on nanoparticle spacing.
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What are Surface Phonon-Polaritons?
Electromagnetic waves that propagate along the interfaces of polar dielectrics.
Results from an evanescent wave’s electric field coupling of infrared photons and optical phonons like two coupled oscillators with the same frequency.
They can enhance fields near the interfaces at infrared frequencies.
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Magnetic Hotplate
Making a Nanocomposite
Silicon Carbide
Nanoparticles Polye
thyle
ne
StirrerToluene
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Making a Nanocomposite cont’d
Preparation Measure out a predetermined ratio of silicon
carbide nanoparticles to polyethylene. .5 grams of nanoparticles is a base reference for
all mass ratios (1:1, 5:1, 10:1, etc…)
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Magnetic Hotplate
Making a Nanocomposite cont’d
Stirrer
Mix Heat / Stir Dry
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AnalysisSmall samples from dried composite are analyzed
using an FTIR (Fourier transform infrared spectroscopy)-ATR (Attenuated Total Reflectance) machine.
Picture courtesy of Stancil group and student Charlezetta E. Stokes
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Preliminary Results Mixing Challenges
Nanoparticles seem to clump together. This may be caused by the nanoparticles not dispersing fully.
Proper mixing will have nanoparticles ~70nm apart.
Polyethylene/Nanoparticle mixture becomes too viscous which effects the mixing of additional polyethylene. Idea: Toluene is evaporating too fast. Improvement: Starting out with a greater amount of
Toluene may solve the predicament. Use toluene volume that is approx. 3 times the volume of polyethylene.
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SEM of 15:1 SiC/PE
SiC Nanoparticles Polyethylene
Picture courtesy of Cory Davis
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Ratio 15:1
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Ratios 1:1, 5:1, 10:1, 20:1
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Picture courtesy of Cory Davis
Figure of a SiC particle of diameter, D, enclosed by a rectangularrepresentation of polyethylene of length = height = D+X
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Early Discussion Ratios 10:1 and lower cracked up when
force was applied to them for FTIR measurement resulting in sloping graphs.
Nanoparticles did not mix well in ratios 5:1 and below.
Phonon-Polariton activity happens between the wavelengths of 766-969 nanometers.
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Next steps…. To use a titration method for mixing
polyethylene and silicon carbide.
Limit toluene evaporation using a lid.
Stir with heat over longer time periods.
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AcknowledgementsI would like to thank
Dr. Kimani A. Stancil, Dr. James S. HammondsCory Davis, Josh Brown
Howard University Physics & Astronomy
National Science Foundation (funding the HU Physics REU)
Virginia Union University (and Dr. Francis Mensah)