By Jesse L. Gray, III Mentors: Dr. Kimani A. Stancil Dr. James S. Hammonds

1. 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

2. Overview • Goal and Importance • What are Surface Phonon-Polaritons? • Making of Nanocomposite • Analysis • Results • Discussion • Next Steps

3. 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.

4. 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.

5. Making a Nanocomposite Stir/Titrate Sonicate Dry Stirrer Magnetic Hotplate

6. Making a Nanocomposite cont’d 1 2 3 5 6 4 8 9 10 10 7 Minutes to wait Toluene Stirrer Magnetic Hotplate 70oC 60 oC

7. 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

8. 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.

9. n2 n1 Picture courtesy of Stancil group and student Charlezetta E. Stokes Polyethylene (PE) Silicon Carbide (SiC)

10. Reflectivity changes with refraction index S-polarized S-polarized P-polarized

11. Polyethylene Carbon Black SiC

12. RESULTS

13. 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.

14. Day 5

17. 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.

18. VT = volume total VNP = volume of nanoparticles X = distance between nanoparticles Figure of a SiC particle of diameter, D, enclosed by a rectangular representation of polyethylene of length = height = D+X VT = volume total VNP = volume of nanoparticles X = distance between nanoparticles

20. Summary • Phonon-Polariton activity happens between the wavelengths of 766-969 nanometers. • Day 5 is dried • Slanting caused by changes in refraction index

21. 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.

22. Acknowledgements I would like to thank Dr. Kimani A. Stancil, Dr. James S. Hammonds Cory Davis, Josh Brown Howard University Physics & Astronomy National Science Foundation (funding the HU Physics REU) Virginia Union University (and Dr. Francis Mensah)