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Exploring Thermal Transfer via Surface Phonon- Polaritons in Tunable Silicon Carbide Bulk Composites. By Jesse L. Gray, III Mentors: Dr. Kimani A. Stancil Dr. James S. Hammonds. Overview. Goal and Importance What are Surface Phonon-Polaritons? Making of Nanocomposite Analysis - PowerPoint PPT Presentation
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EXPLORING THERMAL TRANSFER VIA SURFACE PHONON-POLARITONS IN TUNABLE SILICON CARBIDE BULK
COMPOSITES
By Jesse L. Gray, III
Mentors:Dr. Kimani A. Stancil
Dr. James S. Hammonds
Overview
Goal and Importance What are Surface Phonon-Polaritons? Making of Nanocomposite Analysis Results Discussion Next Steps
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.
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.
Magnetic Hotplate
Making a Nanocomposite
Stirrer
SonicateStir/Titrate
Dry
10
Magnetic Hotplate
Making a Nanocomposite cont’d
Stirrer
Toluene
12345678910
70oC60 oC
Minutes to wait
Changes in Procedure
Initial toluene volume
Cold Mix Mixing mixture at temperature lower than melting
point of polyethylene
“Titration” Adding polyethylene over time
Heat Mix Stirring and leaving the heat on for additional hour
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…)
Measure out the determined amount of polyethylene based on the mass ratio. 5 grams of polyethylene would be needed for a mass
ratio of 10:1
Calculate the volume of polyethylene and multiply it by 3.5. Add that amount of toluene to the silicon carbide.
Picture courtesy of Stancil group and student Charlezetta E. Stokes
Polyethylene (PE)
Silicon Carbide (SiC)
n1
n2
Reflectivity changes with refraction index
S-polarizedS-polarized
P-polarized
Material Refractive Index
Polyethylene 1.5159 - 1.488
Silicon Carbide 2.69026 - 2.55
Carbon Black 1.11-2
Toluene 1.496
Air 1
Polyethylene
SiC
Carbon Black
RESULTS
Kinetics study
Goal: To see how long it took for enough toluene to evaporate before it’s presence was not detected on the FTIR-ATR (Fourier transform infrared spectroscopy – Attenuated Total Reflectance).
What was expected. What was observed.
Importance : Refractive index changes as the components of the nanocomposite changes.
760 810 860 910 96060
65
70
75
80
85
90
95 10:1
Day 1Day 3Day 4Day 5
Cm-1
T%
Increase in Time
Day 5
750 800 850 900 950 10000
5
10
15
20
25
30
1 to 1
Day 1Day 2Day 4Day 5
Cm-1
%T
750 800 850 900 950 100035
40
45
50
55
60
65
70
75
5 to 1
Day 1Day 2Day 3Day 4Day 5
cm-1
%T
750 800 850 900 950 100070
75
80
85
90
15 to 1
Day 1Day 2Day 4Day 5
Cm-1
%T
750 800 850 900 950 100070
75
80
85
90
95
20 to 1
Day 1Day 4Day 5
Cm-1
%T
750 800 850 900 950 10000
10
20
30
40
50
60
70
80
90
100
1 to 15 to 110 to 115 to 120 to 1
Cm-1
%T
Day 5 Averages across all ratios
Increase with decrease in polyethylene
Mixing Challenges Nanoparticles seem to clump together.
This may be caused by the nanoparticles not dispersing fully.
Polyethylene/Nanoparticle mixture becomes too viscous which affects 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. 4 times the volume of polyethylene.
Figure of a SiC particle of diameter, D, enclosed by a rectangularrepresentation of polyethylene of length = height = D+X
VT = volume total
VNP = volume of nanoparticles
X = distance between nanoparticles
Summary
Phonon-Polariton activity happens between the wavelengths of 766-969 nanometers.
Day 5 is dried
Slanting caused by changes in refraction index
Next steps….
To compare the surface phonon-polariton response for one mass ratio with time dependence (Day 1 – Day 5).
To compare the surface phonon-polariton response for different mass ratios on the same day.
Table the SEM determined particle separations versus recipe determined particle separations.
Acknowledgements
I 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)